Patent Application
20210157038
Chemically strengthened glass-based articles are formed by subjecting glass-based substrates to a chemical modification to improve at least one strength-related characteristic, such as hardness, resistance to fracture or surface scratches, etc. Chemically strengthened glass-based articles have found particular use as cover glasses for display-based electronic devices, especially hand-held devices such as smart phones and tablets.
In one method, the chemical strengthening is achieved by an ion-exchange (IOX) process whereby ions in the matrix of a glass-based substrate (“native ions” or “substrate ions”) are replaced by externally introduced (i.e., replacement or in-diffused) ions, e.g., from a molten bath. The strengthening generally occurs when the replacement ions are larger than the native ions (e.g., Na+ or Li+ ions replaced by K+ ions). The IOX process gives rise to an IOX region in the glass that extends from the article surface into the matrix. The IOX region defines within the matrix a refractive index profile having a depth of layer (DOL) that represents a size, thickness or “deepness” of the IOX region as measured relative to the article surface. The refractive index profile also defines stress-related characteristics, including a stress profile, surface stress, depth of compression, center tension, birefringence, etc. The refractive index profile can also define in the glass-based article an optical waveguide that supports a number m of guided modes for light of a given wavelength when the refractive index profile meets certain criteria known in the art.
Prism-coupling systems and methods can be used to measure the spectrum of the guided modes of the planar optical waveguide formed in the glass-based IOX article to characterize one or more properties of the IOX region, such as the refractive index profile and the aforementioned stress-related characteristics. This technique has been used to measure properties of glass-based IOX articles used for a variety of applications, such as for chemically strengthened covers for displays (e.g., for smart phones). Such measurements are used for quality control purposes to ensure that the IOX region has the intended characteristics and falls within the select design tolerances for each of the selected characteristics for the given application.
While prism-coupling systems and methods can be used for many types of conventional glass-based IOX articles, such methods do not work as well and sometimes do not work at all on certain glass-based IOX articles. For example, certain types of IOX glass-based articles are actual dual IOX (DIOX) glass-based articles formed by first and second ion diffusions that give rise to a two-part stress profile. The first part (first region) is immediately adjacent the substrate surface and has a relatively steep slope for the stress change, while the second segment (second region) extends deeper into the substrate but has a relatively shallow slope for the stress change. The first region is referred to as the spike region or just “spike,” while the second region is referred to as the deep region. The optical waveguide is defined by both the spike region and the deep region.
Such two-region profiles result in a relatively large spacing between low-order modes, which have a relatively high effective index, and a very small spacing between high-order modes, which have a relatively low effective index close to the critical angle, which defines the boundary or transition between total-internal reflection (TIR) for guided modes and non-TIR for so-called leaky modes. In a mode spectrum, the critical angle can also be called the “critical angle transition” for convenience. It can happen that a guided mode can travel only in the spike region of the optical waveguide. A guided or leaky mode traveling only in the spike region makes it difficult if not impossible to distinguish between light that is guided only in the spike region and light that is guided in the deep region.
Determining the precise location of the critical angle from the mode spectrum for a glass-based IOX article having a two-region profile is problematic because guided modes that reside close to the critical angle distort the intensity profile at the critical angle transition. This in turn distorts the calculation of the fractional number of mode fringes, and hence the calculation of the depth of the spike region and stress-related parameters, including the calculation of the compressive stress at the bottom of the spike region, which is referred to as the “knee stress” and is denoted CSk.
As it turns out, the knee stress CSk is an important property of a glass-based IOX article and its measurement can be used for quality control in large-scale manufacturing of chemically strengthened glass-based articles. Unfortunately, the above-described measurement problems impose severe restrictions when using a prism-coupling system to make measurements of IOX articles for quality control because an accurate estimation of the knee stress CSk requires that the critical angle transition be accurately established for both the transverse electric (TE) and transverse magnetic (TM) guided modes.
The methods described herein are directed to improving the performance of a prism-coupling system when measuring at least one stress-related characteristic of chemically strengthened articles, and particularly for IOX articles that include a near-surface spike region. The improvement includes a light source comprising multiple light-emitting elements having different measurement wavelengths or alternatively a single wideband light source and multiple narrow-band filters to define the different measurement wavelengths. Measuring chemically strengthened articles at different wavelengths allows for a more accurate estimate of at least one stress-related characteristic. Example stress-related characteristics include stress-related parameters, such as the stress profile, the knee stress CSk, the center tension CT, the tension-strain energy TSE, birefringence, and an estimate of frangibility, which relates to the center tension CT and/or to the tension-strain energy TSE, the spike depth D1, the depth of layer D2 and the refractive index profile n(x).
Examples of the prism-coupling systems and methods include using a prism-coupling system to collect initial TM and TE mode spectra of a chemically strengthened article. In an example, the chemically strengthened article has a refractive index profile with a near-surface spike region and a deep region. TM and TE mode spectra are collected sequentially at two or more different measurement wavelengths, i.e., the different emission wavelengths of the multiple light-emitting elements of the light source or the different measurement wavelengths formed by filtering the wide-band light from a wide-band light source. This results in a set of TM and TE mode spectra for the different measurement wavelengths. The set of TM and TE mode spectra is then evaluated to assess which of the TM and TM mode spectra is best suited for determining at least one stress characteristic. The evaluation can include considering the contrast of the mode lines in the TM and TE mode spectra. The evaluation can also include determining integer and fractional parts of the number of mode lines in the TM mode spectrum and TE mode spectrum and making a selection based on the fractional part (FP) falling into a select range or having a select value, as explained below.
An embodiment of the disclosure is directed to a method of estimating a least one stress-based characteristic of a chemically strengthened article having a refractive index profile with a near-surface spike region and a deep region that define an optical waveguide in a glass-based substrate, comprising: a) using a prism-coupling system having a light source and a coupling prism, sequentially illuminating the glass-based substrate through the coupling prism with measurement light of different wavelengths to generate reflected light containing TM and TE mode spectra for each measurement wavelength to define a set of TM and TE mode spectra; b) examining the set of TM and TE mode spectra to identify a best TM and TE mode spectra of the set of TM and TE mode spectra for providing a most accurate estimate of the at least one stress-based characteristic; and c) estimating the at least one stress-based characteristic using the best TM and TE mode spectra.
Another embodiment of the disclosure is directed to a method of estimating a least one stress-based characteristic of a chemically strengthened article having a refractive index profile with a near-surface spike region and a deep region that define an optical waveguide in a glass-based substrate, comprising: a) using a prism-coupling system having a light source and a coupling prism, sequentially illuminating the glass-based substrate through the coupling prism with broadband measurement light to generate broadband reflected light containing TM and TE mode spectra; b) sequentially narrow-band filtering either the broadband measurement light or the broadband reflected light to form sequential narrow-band reflected light beams having different center wavelengths; c) digitally detecting the sequential narrow-band reflected light beams to capture TM and TE mode spectra for each of the sequential narrow-band reflected light beams; d) examining the set of TM and TE mode spectra to identify a best TM and TE mode spectra of the set of TM and TE mode spectra for providing a most accurate estimate of the at least one stress-based characteristic; and e) estimating the at least one stress-based characteristic using the best TM and TE mode spectra.
Another embodiment of the disclosure is directed to a prism-coupling system for measuring a stress characteristic of a chemically strengthened ion-exchanged (IOX) article having a near-surface spike region and a deep region formed in a glass-based substrate and that define an optical waveguide, comprising: a) a coupling prism having an input surface, an output surface and a coupling surface, and wherein the coupling surface interfaces with the waveguide at a substrate upper surface; b) a light source system that sequentially emits over an input optical path multiple measurement light beams having different measurement wavelengths, wherein the sequentially emitted measurement light beams illuminate the interface through the input surface of the prism, thereby forming sequentially reflected light beams that exit the output surface of the coupling prism and travel over an output optical path, wherein the sequentially reflected light beams defines respective transverse magnetic (TM) mode spectrum and a transverse electric (TE) mode spectrum each having a different one of the measurement wavelengths; c) a photodetector system arranged to receive the sequentially reflected light beams and detect the TM and TE mode spectra for each of the measurement wavelengths to form a set of TM and TE mode spectra; d) a controller configured to perform the acts of: i) processing the set of TM and TE mode spectra to identify a best TM and TE mode spectra of the set of TM and TE mode spectra for providing a most accurate estimate of the at least one stress-based characteristic; and ii) estimating the at least one stress-based characteristic using the best TM and TE mode spectra.
Another embodiment of the disclosure is directed to a prism-coupling system for measuring a stress characteristic of a chemically strengthened ion-exchanged (IOX) article having a near-surface spike region and a deep region formed in a glass-based substrate and that define an optical waveguide, comprising: a) a coupling prism having an input surface, an output surface and a coupling surface, and wherein the coupling surface interfaces with the waveguide at a substrate upper surface; b) a light source system that sequentially emits over an input optical path a broadband light beam that illuminates the interface through the input surface of the prism, thereby forming a reflected light beam that exit the output surface of the coupling prism and travel over an output optical path, wherein the reflected light beam defines a transverse magnetic (TM) mode spectrum and a transverse electric (TE) mode spectrum; c) an optical filter system configured to sequentially insert optical filters having different narrow-band wavelength transmissions into either the input optical path or the output optical path to define sequentially reflected light beams each having a different measurement wavelength; d) a photodetector system arranged to receive the sequential reflected light beams and detect the TM and TE mode spectra for each of the measurement wavelengths to form a set of TM and TE mode spectra; and e) a controller configured to perform the acts of: i) identifying a best TM and TE mode spectra of the set of TM and TE mode spectra for providing a most accurate estimate of the at least one stress-based characteristic; and ii) estimating the at least one stress-based characteristic using the best TM and TE mode spectra.
According to aspect (1), a method of estimating a least one stress-based characteristic of a chemically strengthened article having a refractive index profile with a near-surface spike region and a deep region that define an optical waveguide in a glass-based substrate is provided. The method comprises: a) using a prism-coupling system having a light source and a coupling prism, sequentially illuminating the glass-based substrate through the coupling prism with measurement light of different wavelengths to generate reflected light containing TM and TE mode spectra for each measurement wavelength to define a set of TM and TE mode spectra; b) examining the set of TM and TE mode spectra and identifying a best TM and TE mode spectra of the set of TM and TE mode spectra for providing a most accurate estimate of the at least one stress-based characteristic; and c) estimating the at least one stress-based characteristic using the best TM and TE mode spectra.
According to aspect (2), the method of aspect (1) is provided, wherein the at least one stress-related characteristic comprises at least one of: a stress profile, a knee stress, a center tension, a tension-strain energy, a birefringence, a frangibility, a spike depth, a depth of layer, and a refractive index profile.
According to aspect (3), the method of any of aspect (1) to the preceding aspect is provided, wherein each of the TM and TE mode spectra has fringes with a fringe contrast, a critical transition and a fringe count with an integer part and a fractional part FP, and wherein identifying a best TM and TE mode spectra of the set of TM and TE mode spectra comprises at least one of: selecting the TM and TE mode spectra having the greatest fringe contrast; selecting the TM and TE mode spectra having respective fractional parts FP in a range between 0.1 and 0.85; and selecting the TM and TE mode spectra where the respective fringes are least affected by the respective critical transitions.
According to aspect (4), the method of aspect (3) is provided, wherein the fractional part FP is between 0.15 and 0.8.
According to aspect (5), the method of any of aspect (1) to the preceding aspect is provided, wherein the different measurement wavelengths fall within a wavelength range from 350 nm to 850 nm.
According to aspect (6), the method of aspect (5) is provided, wherein the different measurement wavelengths fall within a wavelength range from 540 nm to 650 nm.
According to aspect (7), the method of any of aspect (1) to the preceding aspect is provided, wherein the prism-coupling system comprises a light source comprising multiple light-emitting elements, wherein each of light-emitting elements emits light at one of the different measurement wavelengths, and wherein changing the measurement configuration includes translating the light source device so that the multiple light-emitting devices are sequentially aligned with an input optical axis that runs between the light source and a coupling prism.
According to aspect (8), the method of aspect (7) is provided, wherein the multiple light-emitting elements comprise light-emitting diodes or laser diodes.
According to aspect (9), the method of any of aspect (7) to the preceding aspect is provided, wherein the different wavelengths of the different light-emitting elements differ by between 1% and 25%.
According to aspect (10), the method of aspect (9) is provided, wherein the different wavelengths of the different light-emitting elements differ by between 3% and 11%.
According to aspect (11), the method of any of aspect (1) to the preceding aspect is provided, wherein the light source device is mechanically connected to a motion control system, and wherein said translating of the light source device is carried out by activating the motion control system.
According to aspect (12), the method of aspect (11) is provided, wherein the motion control comprises a linear actuator.
According to aspect (13), the method of any of aspect (1) to the preceding aspect is provided, wherein the measurement light from each of the light-emitting elements has a wavelength bandwidth centered around a central wavelength, and further comprising sequentially passing the measurement light of the different wavelengths through respective narrow-pass optical filters centered on the respective different central wavelengths to reduce the wavelength bandwidth of the measurement light.
According to aspect (14), the method of any of aspects (1) to (6) is provided, wherein the prism-coupling system comprises a light source comprising a broadband light-emitting element that emits broadband light, and wherein changing the measurement configuration includes sequentially filtering the broadband light with two or more narrow-band optical filters centered on different measurement wavelengths.
According to aspect (15), the method of aspect (14) is provided, wherein the light-emitting element comprises multiple light emitters.
According to aspect (16), the method of any of aspect (14) to the preceding aspect is provided, wherein the two or more narrow-band optical filters are supported in a filter member and further comprising moving the filter member to sequentially place the narrow-band optical filters either in operable alignment with the broadband light-emitting element or within the reflected light.
According to aspect (17), the method of aspect (16) is provided, wherein the filter member comprises a filter wheel and said moving of the filter member comprises rotating the filter member.
According to aspect (18), the method of any of aspect (16) to the preceding aspect is provided, further comprising tracking a position of the filter member using a detection system to ensure alignment of a select one of the narrow-band optical filters either with the broadband light-emitting element or within the reflected light.
According to aspect (19), the method of any of aspects (14) to (16) is provided, wherein the two or more narrow-band optical filters are supported by a support frame and linearly translating the support frame to sequentially place the narrow-band optical filters in operable alignment with the broadband light-emitting element.
According to aspect (20), the method of aspect (19) is provided, wherein the linearly translating of the support frame is performed by activating a motion control system mechanically coupled to the support frame.
According to aspect (21), the method of aspect (20) is provided, wherein the motion control system comprises a linear actuator and wherein said linearly translating comprises activating the linear actuator.
According to aspect (22), the method of any of aspect (1) to the preceding aspect is provided, wherein the examining of the set of TM and TE mode spectra comprises detecting each of the TM and TE mode spectra with a digital detector and digitally processing respective mode lines of the TM and TE mode spectra to establish a mode line contrast.
According to aspect (23), the method of any of aspect (1) to the preceding aspect is provided, comprising optically coupling the coupling prism to the chemically strengthened article by an index matching fluid.
According to aspect (24), a method of estimating a least one stress-based characteristic of a chemically strengthened article having a refractive index profile with a near-surface spike region and a deep region that define an optical waveguide in a glass-based substrate is provided. The method comprises: a) using a prism-coupling system having a light source and a coupling prism, sequentially illuminating the glass-based substrate through the coupling prism with broadband measurement light to generate broadband reflected light containing TM and TE mode spectra; b) sequentially narrow-band filtering either the broadband measurement light or the broadband reflected light to form sequential narrow-band reflected light beams having different center wavelengths; c) digitally detecting the sequential narrow-band reflected light beams to capture TM and TE mode spectra for each of the sequential narrow-band reflected light beams; d) examining the set of TM and TE mode spectra to identify a best TM and TE mode spectra of the set of TM and TE mode spectra for providing a most accurate estimate of the at least one stress-based characteristic; and e) estimating the at least one stress-based characteristic using the best TM and TE mode spectra.
According to aspect (25), the method of aspect (24) is provided, wherein the at least one stress-related characteristic comprises at least one of: a stress profile, a knee stress, a center tension, a tension-strain energy, a birefringence, a frangibility, a spike depth, a depth of layer, and a refractive index profile.
According to aspect (26), the method of any of aspect (24) to the preceding aspect is provided, wherein each of the TM and TE mode spectra has fringes with a fringe contrast, a critical transition and a fringe count with an integer part and a fractional part FP, and wherein identifying a best TM and TE mode spectra of the set of TM and TE mode spectra comprises at least one of: selecting the TM and TE mode spectra having the greatest fringe contrast; selecting the TM and TE mode spectra having respective fractional parts FP in a range between 0.1 and 0.85; and selecting the TM and TE mode spectra where the respective fringes are least affected by the respective critical transitions.
According to aspect (27), the method of aspect (26) is provided, wherein the fractional part FP is between 0.15 and 0.8.
According to aspect (28), the method of any of aspect (24) to the preceding aspect is provided, wherein the different measurement wavelengths fall within a wavelength range from 350 nm to 850 nm.
According to aspect (29), the method of aspect (28) is provided, wherein the different measurement wavelengths fall within a wavelength range from 540 nm to 650 nm.
According to aspect (30), the method of any of aspect (24) to the preceding aspect is provided, wherein the different wavelengths of the different light-emitting elements differ by between 1% and 25%.
According to aspect (31), the method of aspect (30) is provided, wherein the different wavelengths of the different light-emitting elements differ by between 2% and 15%.
According to aspect (32), the method of aspect (31) is provided, wherein the different wavelengths of the different light-emitting elements differ by between 3% and 11%.
According to aspect (33), the method of any of aspect (24) to the preceding aspect is provided, wherein the narrow band filtering comprises sequentially inserting narrow band filters having the different center wavelengths into either the broadband measurement light or the broadband reflected light.
According to aspect (34), the method of aspect (33) is provided, wherein the narrow band filters are supported in a filter member and wherein act of sequentially inserting comprises moving the filter member.
According to aspect (35), the method of aspect (34) is provided, wherein the filter member comprises a filter wheel and wherein said moving the filter member comprises rotating the filter wheel.
According to aspect (36), the method of any of aspect (34) to the preceding aspect is provided, further comprising tracking a position of the filter member using a detection system.
According to aspect (37), the method of any of aspects (34) to (36) is provided, wherein said digitally detecting comprises focusing the sequential narrow-band reflected light beams onto a digital detector using a collection optical system, and wherein the filter member at least partially resides within the collection optical system.
According to aspect (38), the method of any of aspects (34) to (36) is provided, wherein the said digitally detecting comprises focusing the sequential narrow-band reflected light beams onto a digital detector using a collection optical system, and wherein the filter member resides between the coupling prism and the collection optical system.
According to aspect (39), the method of any of aspect (24) to the preceding aspect is provided, wherein the sequential narrow-band reflected light beams each has a wavelength band of 10 nm or less.
According to aspect (40), the method of aspect (39) is provided, wherein the sequential narrow-band reflected light beams each has a wavelength band of 6 nm or less.
According to aspect (41), a prism-coupling system for measuring a stress characteristic of a chemically strengthened ion-exchanged (IOX) article having a near-surface spike region and a deep region formed in a glass-based substrate and that define an optical waveguide is provided. The prism-coupling system comprising: a) a coupling prism having an input surface, an output surface and a coupling surface, and wherein the coupling surface interfaces with the waveguide at a substrate upper surface; b) a light source system that sequentially emits over an input optical path multiple measurement light beams having different measurement wavelengths, wherein the sequentially emitted measurement light beams illuminate the interface through the input surface of the prism, thereby forming sequentially reflected light beams that exit the output surface of the coupling prism and travel over an output optical path, wherein the sequentially reflected light beams defines respective transverse magnetic (TM) mode spectrum and a transverse electric (TE) mode spectrum each having a different one of the measurement wavelengths; c) a photodetector system arranged to receive the sequentially reflected light beams and detect the TM and TE mode spectra for each of the measurement wavelengths to form a set of TM and TE mode spectra, d) a controller configured to perform the acts of: a. processing the set of TM and TE mode spectra to identify a best TM and TE mode spectra of the set of TM and TE mode spectra for providing a most accurate estimate of the at least one stress-based characteristic; and b. estimating the at least one stress-based characteristic using the best TM and TE mode spectra.
According to aspect (42), the prism-coupling system of aspect (41) is provided, wherein the light source system comprises a light source device that operably supports multiple light-emitting elements having different measurement wavelengths.
According to aspect (43), the prism-coupling system of aspect (42) is provided, wherein the light source device is mechanically connected to a motion control system that moves the light source device so that the light-emitting elements sequentially emit measurement light of the different measurement wavelengths over the input optical path.
According to aspect (44), the prism-coupling system of aspect (43) is provided, wherein the motion control system comprises a linear actuator connected to the light source by a drive shaft.
According to aspect (45), the prism-coupling system of any of aspect (42) to the preceding aspect is provided, wherein the sequentially emitted measurement light beams each has an optical bandwidth and further comprising multiple narrow-band optical filters, wherein the optical filters are supported in a support frame so that each of the light-emitting elements of the multiple light-emitting elements is optically aligned with one of the optical filters to reduce the optical bandwidth of the sequentially emitted measurement light beams.
According to aspect (46), the prism-coupling system of aspect (41) is provided, wherein the light source comprises a broadband light-emitting element that emits broadband light, and further comprising an array of optical filters each having a different central wavelength, wherein the optical filters are supported by a movable support frame so that the optical filters can be sequentially inserted into the broadband light to generate the sequential measurement light beams having the different measurement wavelengths.
According to aspect (47), the prism-coupling system of aspect (46) is provided, wherein the movable support frame comprises a rotatable filter member.
According to aspect (48), the prism-coupling system of aspect (46) is provided, wherein the movable support frame is operably attached to a linear actuator configured to translate the support frame to sequentially insert the optical filters into the broadband light.
According to aspect (49), the prism-coupling system of any of aspect (41) to the preceding aspect is provided, wherein the sequentially emitted measurement light beams each has an optical bandwidth of less than 10 nm.
According to aspect (50), the prism-coupling system of any of aspect (41) to the preceding aspect is provided, wherein the different measurement wavelengths consist of three different measurement wavelengths.
According to aspect (51), the prism-coupling system of any of aspect (41) to the preceding aspect is provided, wherein the different measurement wavelengths fall within the wavelength range from 350 nm to 850 nm.
According to aspect (52), the prism-coupling system of aspect (51) is provided, wherein the different measurement wavelengths fall within a wavelength range from 540 nm to 650 nm.
According to aspect (53), a prism-coupling system for measuring a stress characteristic of a chemically strengthened ion-exchanged (IOX) article having a near-surface spike region and a deep region formed in a glass-based substrate and that define an optical waveguide is provided. The prism-coupling system comprises: a) a coupling prism having an input surface, an output surface and a coupling surface, and wherein the coupling surface interfaces with the waveguide at a substrate upper surface; b) a light source system that sequentially emits over an input optical path a broadband light beam that illuminates the interface through the input surface of the prism, thereby forming a reflected light beam that exit the output surface of the coupling prism and travel over an output optical path, wherein the reflected light beam defines a transverse magnetic (TM) mode spectrum and a transverse electric (TE) mode spectrum; c) an optical filter system configured to sequentially insert optical filters having different narrow-band wavelength transmissions into either the input optical path or the output optical path to define sequentially reflected light beams each having a different measurement wavelength; d) a photodetector system arranged to receive the sequential reflected light beams and detect the TM and TE mode spectra for each of the measurement wavelengths to form a set of TM and TE mode spectra; e) a controller configured to perform the acts of: a. identifying a best TM and TE mode spectra of the set of TM and TE mode spectra for providing a most accurate estimate of the at least one stress-based characteristic; and b. estimating the at least one stress-based characteristic using the best TM and TE mode spectra.
According to aspect (54), the prism-coupling system of aspect (53) is provided, wherein the optical filter system comprises a movable filter member mechanically connected to a drive motor configured to move the movable filter member.
According to aspect (55), the prism-coupling system of aspect (54) is provided, further comprising a detection system for detecting a position of the movable filter member.
According to aspect (56), the prism-coupling system of any of aspect (54) to the preceding claim is provided, wherein the moveable filter member comprises a rotatable filter wheel.
According to aspect (57), the prism-coupling system of any of aspect (53) to the preceding claim is provided, wherein said identifying the best TM and TE mode spectra comprises performing a fringe count to determine an integer part of the fringe count and a fractional part of the fringe count and selecting the TM and TE mode spectra based on the fractional part of the fringe count falling within a select range.
According to aspect (58), the prism-coupling system of any of aspect (53) to the preceding claim is provided, wherein the sequentially reflected light beams each has a wavelength band of less than 10 nm.
According to aspect (59), the prism-coupling system of any of aspect (53) to the preceding claim is provided, wherein the different measurement wavelengths fall within the wavelength range from 350 nm to 850 nm.
According to aspect (60), the prism-coupling system of aspect (59) is provided, wherein the different measurement wavelengths fall within a wavelength range from 540 nm to 650 nm.
Additional features and advantages are set forth in the Detailed Description that follows, and in part will be apparent to those skilled in the art from the description or recognized by practicing the embodiments as described in the written description and claims hereof, as well as the appended drawings. It is to be understood that both the foregoing general description and the following Detailed Description are merely exemplary, and are intended to provide an overview or framework to understand the nature and character of the claims.
The accompanying drawings are included to provide a further understanding, and are incorporated in and constitute a part of this specification. The drawings illustrate one or more embodiment(s), and together with the Detailed Description explain the principles and operation of the various embodiments. As such, the disclosure will become more fully understood from the following Detailed Description, taken in conjunction with the accompanying Figures, in which:
Reference is now made in detail to various embodiments of the disclosure, examples of which are illustrated in the accompanying drawings. Whenever possible, the same or like reference numbers and symbols are used throughout the drawings to refer to the same or like parts. The drawings are not necessarily to scale, and one skilled in the art will recognize where the drawings have been simplified to illustrate the key aspects of the disclosure.
The acronym IOX can mean either “ion exchange” or “ion exchanged,” depending on the context of the discussion. An “IOX article” means an article formed using at least one 10× process. Thus, an article formed by a DIOX process is referred to herein as an IOX article, though it could also be referred to as a DIOX article.
The term “glass based” is used herein to describe a material, article, matrix, substrate, etc., means that the material, article, matrix, material, substrate, etc. can comprise or consist of either a glass or a glass ceramic.
The compressive stress profile for an IOX article is denoted CS(x) and is also referred to herein as just the stress profile. The surface compressive stress or just “surface stress” for the stress profile is denoted CS and is the value of the compressive stress profile CS(x) for x=0, i.e., CS=CS(0), where x=0 corresponds to the surface of the IOX article.
The depth of compression DOC is the x distance into the IOX article as measured from the surface of the IOX article to where the compressive stress CS(x) or CS′(x) crosses zero.
The knee stress is denoted CSk and is the amount of compressive stress at a knee transition point (depth D1) between a spike region (R1) and a deep region (R2), i.e., CS(D1)=CSk.
The spike region R1 has a spike depth from the substrate surface that is denoted both as D1 and DOLSP, with the latter also being referred to as the spike depth of layer. The spike region is also referred as a “near-surface spike region” to clarify the distinction with the deep region.
The deep region R2 has a depth D2 which is also denoted as the total depth of layer DOLT for the total IOX region.
The acronym FWHM means “full-width half maximum.”
The terms “preferred measurement window” and “extended measurement window” are synonymous.
The abbreviation μm stands for micron or micrometer, which is 10−6 meter.
The abbreviation nm stands for nanometer, which is 10−9 meter.
The claims as set forth below are incorporated into and constitute part of this Detailed Description.
The term “contrast” as used herein with respect mode lines or fringes of a mode spectrum means a measure of the difference between a minimum intensity value and a maximum intensity value, and can include a rate of change in the intensity. One example measure of contrast C=(IMAX−IMIN)/(IMAX+IMIN) where IMAX and IMIN are the maximum and minimum intensity values. Other measures of contrast used in the art of image processing can also be used.
Example prism-coupling systems and measurement methods are described for example in: U.S. Application Publication No. 2016/0356760, published Dec. 8, 2016, entitled “METHODS OF CHARACTERIZING ION-EXCHANGED CHEMICALLY STRENGTHENED GLASSES CONTAINING LITHIUM (also published as WO 2016/196748 A1); U.S. Pat. No. 9,897,574, issued Feb. 20, 2018, entitled “METHODS OF CHARACTERIZING ION-EXCHANGED CHEMICALLY STRENGTHENED GLASSES CONTAINING LITHIUM”; and U.S. Application Publication No. 2019/0033144, published Jan. 31, 2019, “METHODS OF IMPROVING THE MEASUREMENT OF KNEE STRESS IN ION-EXCHANGED CHEMICALLY STRENGTHENED GLASSES CONTAINING LITHIUM,” and U.S. Pat. No. 9,534,981, issued Jan. 3, 2017, “PRISM-COUPLING SYSTEMS AND METHODS FOR CHARACTERIZING ION-EXCHANGE WAVEGUIDES WITH LARGE DEPTH-OF-LAYER,” each of which is incorporated herein by reference in its entirety.
U.S. Pat. No. 10,732,059, issued Aug. 4, 2020, entitled “PRISM-COUPLING STRESS METER WITH WIDE METROLOGY PROCESS WINDOW,” is also incorporated herein by reference in its entirety.
IOX Article
The substrate 20 includes in the matrix 21 substrate ions IS, which exchange for first ions I1 and second ions I2. The first and second ions I1 and I2 can be introduced into the matrix 21 either sequentially or concurrently using known techniques. For example, second ions I2 can be K+ ions introduced via a KNO3 bath for strengthening, prior to introducing first ions I1 that can be Ag+ ions introduced via a AgNO3-containing bath to add the anti-microbial property adjacent surface 22. The circles in
In addition, ions I1 may be present in significant numbers in both regions R1 and R2 (see
The deep region R2 may be produced in practice prior to the spike region R1. The spike region R1 is immediately adjacent the substrate surface 22 and is relatively steep and shallow (e.g., D1 is a few microns), whereas the deep region R2 is less steep and extends relatively deep into the substrate to the aforementioned depth D2. In an example, the spike region R1 has a maximum refractive index no at substrate surface 22 and steeply tapers off to an intermediate index ni (which could also be called the “knee index”), while the deep region R2 tapers more gradually from the intermediate index down to the substrate (bulk) refractive index ns. It is emphasized here that other IOX processes can result in a steep and shallow near-surface refractive index change and that a DIOX process is discussed here by way of illustration.
In some examples, the IOX article 10 is frangible while in other examples, it is non-frangible, according to the frangibility criteria set forth below.
Prism-Coupling System
The prism-coupling system 28 includes a support stage 30 configured to operably support the IOX article 10. The prism-coupling system 28 also includes a coupling prism 40 that has an input surface 42, a coupling surface 44 and an output surface 46. The coupling prism 40 has a refractive index np>n. The coupling prism 40 is interfaced with the IOX article 10 being measured by bringing coupling-prism coupling surface 44 and the surface 22 into optical contact, thereby defining an interface 50 that in an example can include an interfacing (or index-matching) fluid 52 having a thickness TH. In an example, the prism-coupling system 28 includes an interfacing fluid supply 53 fluidly connected to the interface 50 to supply the interfacing fluid 52 to the interface. This configuration also allows for different interfacing fluids 52 with different refractive indices to be deployed. Thus, in an example, the refractive index of the interfacing fluid 52 can be changed by operation of the interfacing fluid supply 53 to add a higher-index or lower-index interfacing fluid. In an example, the interfacing fluid supply 53 is operably connected to and controlled by the controller 150.
In an exemplary measurement, a vacuum system 56 pneumatically connected to the interface 50 can be used to control the thickness TH by changing the amount of vacuum at the interface. In an example, the vacuum system is operably connected to and controlled by the controller 150.
The prism-coupling system 28 includes input and output optical axes A1 and A2 that respectively pass through the input and output surfaces 42 and 46 of the coupling prism 40 to generally converge at the interface 50 after accounting for refraction at the prism/air interfaces.
The prism-coupling system 28 includes, in order along the input optical axis A1, a light source system 60 that emits measurement light 62 in the general direction along the input optical axis A1. The measurement light 62 has a measurement wavelength λ, which can be sequentially changed during the operation of the prism-coupling system 28 to generate sequential input (measurement) light beams 62B1, 62B2, . . . having different measurement wavelengths λ. Example configurations of the light source system 60 that can be used to sequentially change the measurement wavelength λ are described in greater detail below. Note that the input optical axis A1 runs between the light source system 60 and the coupling prism 40. A focusing optical system 80 that includes a focusing lens 82 is used to focus the measurement light to form focused measurement light 62F.
The prism-coupling system 28 also includes, in order along the output optical axis A2 from the coupling prism 40, a collection optical system 90 having a focal plane 92 and a focal length f and that receives reflected light 62R as explained below, a TM/TE polarizer 100, and a photodetector system 130. In an example, the reflected light 62R comprises sequentially reflected light beams 62R1, 62R2, . . . each having a different measurement wavelength, as explained in greater detail below. The portion of the prism-coupling system 28 downstream of the coupling prism 40 (as defined by the direction of travel of the measurement light 62) is referred to as the detector side of the system.
The input optical axis A1 defines the center of an input optical path OP1 between the light source system 60 and the coupling surface 44. The input optical axis A1 also defines a coupling angle θ with respect to the surface 22 of the IOX article 10 being measured.
The output optical axis A2 defines the center of an output optical path OP2 between the coupling surface 44 and the photodetector system 130. Note that the input and output optical axes A1 and A2 may be bent at the input and output surfaces 42 and 46, respectively, due to refraction. They may also be broken into sub-paths by inserting mirrors (not shown) into the input and output optical paths OP1 and/or OP2.
In an example, the photodetector system 130 includes a detector (camera) 110 and a frame grabber 120. In other embodiments discussed below, the photodetector system 130 includes a CMOS or CCD camera.
The photosensitive surface 112 resides in the focal plane 92 of the collecting optical system 90, with the photosensitive surface being generally perpendicular to the output optical axis A2. This serves to convert the angular distribution of the reflected light 62R exiting the coupling prism output surface 46 to a transverse spatial distribution of light at the sensor plane of the detector 110. In an example embodiment, the photosensitive surface 112 comprises pixels, i.e., the detector 110 is a digital detector, e.g., a digital camera.
Splitting the photosensitive surface 112 into TE and TM sections 112TE and 112TM as shown in
The TM mode spectrum 113TM includes mode lines or fringes 115TM while the TE mode spectrum 113TE includes mode lines or fringes 115TE. The mode lines or fringes 115TM and 115TE can either be bright lines or dark lines, depending on the configuration of the prism-coupling system 28. In
The stress characteristics are calculated based on the difference in positions of the TM and TE fringes 115TM and 115TE in the mode spectrum 113. At least two fringes 115TM for the TM mode spectrum 113TM and at least two fringes 115TE for the TE mode spectrum 113TE are needed to calculate the surface stress CS. Additional fringes are needed to calculate the stress profile CS(x). The TM and TE fringes 115TM and 115TE also need to have a suitable contrast so that their positions can be accurately determined.
With reference again to
Example Light Source Systems
A. Translatable Light Source Device
Three example light-emitting elements 61 are shown in
In the example shown, each light-emitting element 61 is encapsulated within a translucent case 63 (e.g., cases 63a, 63b and 63c) that in an example can act as a lens. Each light-emitting element 61 has a central axis AE, with the axes for light-emitting elements 61a, 61b and 61c respectively denoted as AEa, AEb and AEc. Note that three light-emitting elements 61 are shown by way of example and that fewer (i.e., two) light-emitting elements 61 can be used or more than three light-emitting elements can be used.
The light source system 60 also can include an array of two or more optical filters 66 respectively operably disposed adjacent the light-emitting elements 61.
With reference again to
The motion control system 250 can be electrically connected to the controller 150, which can control the linear actuator via an actuator control signal SA to move the light source device 220 back and forth relative to the input optical axis A1 (e.g., in a direction perpendicular thereto). This lateral movement can be used to position (translate) a select one of the light-emitting elements 61a, 61b or 61c to be co-axial with or otherwise aligned with the input optical axis A1, as illustrated in the examples of
When the light source 60 in
B. Broadband Light-Emitting Element with Translatable Filters
The top section 241 of the support frame 240 has a top surface 242, a proximal end 243 and a distal end 244. The top surface 242 includes at least one guide feature 245, such as a pair of guide rails or guide grooves, as best seen in
The proximal end 243 of the top section 241 is operably engaged by the motion control system 250, e.g., by the drive shaft 252 of the linear actuator 251, to drive the lateral movement of the top section 241.
C. Light-Emitting Element with Rotatable Filters
The light source system 60 includes a drive motor 300 having a drive shaft 302 that is operably attached to the central section 260 so that the support frame 240 can be rotated about the rotation axis AR. In an example, the drive motor 300 is configured to rotate the support frame 240 in steps (e.g., angular increments) to position a select one of the optical filters 66 so that it resides just above the broadband light-emitting element 61, i.e., in the input optical path OP1. In an example, the drive motor 300 is connected to and controlled by the controller 150. The support frame 240 and optical filters 66 supported thereby constitute a filter member 320. In an example, the filter member comprises a filter wheel. The filter member 320, the drive motor 300 and the drive shaft 302 operably connected to the filter member at the central section 260 of the support frame 240 constitute an optical filter system 350.
B. Optical Filter System in the Collection Optical System
In the example of
In an example, the TM/TE polarizer 100 can also be positioned within the collection optical system 90 so that the substantially collimated reflected light 62R can also pass through the TM/TE polarizer at substantially normal incidence. The second lens L2 can serve as a focusing lens that directs the wavelength-filtered reflected measurement light (i.e., the sequential narrow-band reflected light beams 62R1, 62R2, . . . ) to the detector 110.
In an example, a reference feature 270 is included on the guide member 320. The position of the reference feature 270 can be detected by a detection system 420. In an example, the reference feature 270 can be a protrusion or recess and the detection system 420 can be a distance sensor that senses a distance to the filter member 320, and wherein the distance is changed by the protrusion or recess. In another example, the reference feature 270 can be a reflective element, a bar code or like indicia and the detection system 420 can be scanner or machine vision system, etc. The detection system 420 and the drive motor 300 can be operably connected to the controller 150. The detection system 420 can provide to the controller 150 a detection signal SD representative of a rotational position of the filter member 320 and thus the relative positions of the filters 66 relative to the output optical path OP2. The controller 150 can also send a motor control signal SM to the drive motor 300 to cause the drive motor to place the filter member 320 in a select rotational position, e.g., with a select one of the filters 66 in the output coupling path OP2.
Measuring the IOX Article Using Different Measurement Wavelengths
A proper measurement of a stress characteristic of the IOX article 10 conventionally requires that the prism-coupling system 28 couple the focused measurement light 62F from the light source 60 (by focusing optical system 80) into a sufficient number of the guided modes supported by the IOX waveguide 26 so that most if not all of the refractive index profile in the spike region R1 as well as the deep region R2 is sampled so that the measured mode spectrum 113 is complete and accurate, i.e., includes information about the entire IOX region 24 and not just a one part of the IOX region.
When a guided or leaky mode associated with the spike region R1 has an effective index that is close to the critical angle, determining the precise location of the critical angle transition 116 in the mode spectrum 113 can be problematic. This is because the usual location of the maximum slope in the intensity profile can correspond to a slightly different effective index than the actual effective index at the spike depth D1, i.e., at the knee KN formed by the transition between the spike region and the deep region R2 (see
As noted above, the resonance caused by the nearby guided or leaky mode in the effective-index spectrum can cause a significant change in the shape of the intensity distribution in the vicinity of the effective index corresponding to the index at the knee KN. Also as noted above, this can substantially distort the calculation of the fractional number of TE and TM fringes 115TE and 115TM, and hence of the spike depth D1, and thus the calculation of the knee stress CSk. This is particularly true for Li-based glass substrates 20 that undergo a DIOX process using Na+ and K+ ions to form the IOX article 10.
The above-described calculation distortions impose severe restrictions when using prism-coupling measurements for quality control of IOX articles 10 since an accurate estimation of the knee stress CSk is only possible in a narrow range of conditions (i.e., a narrow measurement process window) where the critical-angle intensity transitions 116 (see
The systems and methods disclosed herein allow for making measurements of the IOX article 10 using different measurement wavelengths λ to obtain TM and TE mode spectra 113TM and 113TE having suitable contrast for performing an accurate measurement of a stress characteristic of the IOX article. This includes sequentially changing the measurement wavelength λ so that different measurement wavelengths can be sequentially coupled into the waveguide 26 of the IOX article 10 to obtain TM and TE mode spectra 113TM and 113TE for a preferred measurement window.
In a first step of the method, the IOX article 10 is loaded into the prism-coupling system 28 and a first mode spectrum 113 is collected as described above for a first measurement wavelength λ.
In a second step of the method, the first TM and TE spectra 113TM and 113TE are processed to obtain a TM and TE signal of intensity versus position of the respective fringes 115TM and 115TE captured by the photosensitive surface 112 of the photodetector system 130. This is equivalent to the intensity vs. coupling angle θ, which is also equivalent to the intensity vs. effective index neff, as there is a one-to-one relationship between position on the photosensitive surface 112, the coupling angle θ, and the effective index neff of guided optical modes propagating in the waveguide 26 defined by the IOX region 24 in the IOX article 10.
In a third step, the intensity versus position data from the second step is used to establish whether the first TM and TE mode spectra 113TM and 113TE were obtained (or reside in) a preferred measurement window of the prism-coupling system 28. In one example, this includes determining the fractional part of the full (real-number) mode count or fringe count for the TM mode spectrum 113TM and the TE mode spectrum 113TE. The full mode count includes an integer portion equal to the number of guided modes for the specific polarization (TM or TE), which is the same as the number of fringes 115TM or 115TE occurring in the TIR section 117 of the respective mode spectra 113TM or 113TE at the measurement wavelength. The number of TM fringes 115TM is NTM while the number of TE fringes 115TE is NTE.
An aspect of the methods disclosed herein involves determining a fractional part FP of the number of modes (mode number) for both the TE mode spectrum 113TE and the TM mode spectrum 113TM.
In an example, the fractional part FP of the mode number is determined by comparing the distance between the last guided mode having the lowest effective index neff, and the effective index neff corresponding to the critical angle transition 116. For coupling angles θ beyond the critical angle, only part of the incident light 62F is reflected to form reflected light 62R, with the non-reflected portion of the incident light penetrating the IOX article 10 substantially deeper than the spike depth D1 as a leaky mode or a radiation mode.
The effective index neff corresponding to the critical angle is referred to as the “critical index” and is denoted ncrit. In some cases, the critical index ncrit can equal the substrate refractive index ns. For example, this situation can arise when the IOX article 10 is formed from an Li-containing glass substrate 20 that is chemically strengthened in a bath containing Na+ (e.g., NaNO3).
The distance between the last guided mode and the critical angle ncrit corresponds to the difference Δnf in effective index between the index of the last guided mode and the critical index is given by:
Δnf=min(neff)−ncrit
where min(neff) is the smallest of the effective indices of all guided modes for the specific polarization (TM or TE), and ncrit is the critical index for the same polarization.
The fractional part FP of the mode count (i.e., number of fringes) NTM or NTE is found by examining the space between the last guided mode 115TE or 115TM and the critical index ncrit. In some embodiments, the fractional part of the TM or TE mode count is determined by comparing Δnf to the expected spacing to the next mode by extrapolating the dependence of effective index on the mode count. In some embodiments, a fit of the dependence of effective index neff on the mode count can be obtained from the integer-numbered guided modes. The fit is then extrapolated, and a mode number is assigned to the critical angle from the value of the mode count NTM or NTE at which the extrapolated function equates to the measured ncrit. This same procedure may be performed directly using the position of fringes 115TM or 115TE in the given mode spectrum 113TM or 113TE versus the fringe number, or an angle in the angular spectrum versus fringe number.
With continuing reference to
Another method of determining the fractional part FP of the fringe count is when there are only two or three modes. In this case, one can approximate the distance DVF by the spacing MS between the two modes closest to the TIR-PIR transition, as also shown in
In one example, to be within the preferred measurement window, the fractional part FP of the fringe count NTM or NTE is within a select range. In one example, the range on the fraction portion FP of the fringe count is 0.1 to 0.85. In another example, the fractional part FP of the fringe count can be greater than 0.15. In another example, the fractional part FP of the fringe count can be below 0.8, e.g., smaller than 0.75, or smaller than 0.70. Thus, example ranges on FP include 0.15 and 0.75 or 0.15 and 0.70.
In an example, TM and TE mode spectra 113TM and 113TE having fractional parts FP that fall within at least one of the example FP ranges set forth above can be taken as a “best” TM and TE mode spectra from a set of TM and TE mode spectra taken at different wavelengths. In another example, the TM and TE mode spectra 113TM and 113TE having the greatest fringe contrast is taken as the “best” TM and TE mode spectra from a set of TM and TE mode spectra taken at different wavelengths. In an example, the best TM and TE mode spectra from a set of TM and TE mode spectra taken at different wavelengths has the greatest fringe contrast and has an fractional part within one of the FP ranges cited above. If multiple pairs of TM and TE mode spectra 113TM and 113TE fall within a select FP ranges, then in an example the TM and TE mode spectra whose modes (fringes) are least affected (i.e., least distorted) by the critical angle transitions 116TM and 116TE is selected. Various selection criteria for what constitutes when a mode (fringe) is least affected by the corresponding critical transition are discussed below.
If the fractional part FP of at least one of the TM mode spectrum 113M and the TE mode spectrum 113TE is outside of the select range, then the prism-coupling system 28 is set to a different measurement condition that brings the fraction portion FP of the fringe count to within the select range, which in turn allows for determining the at least one stress parameter of the IOX article 10 with better accuracy.
In another example, to be within the preferred measurement window, there can be no guided or a leaky mode close enough to the critical index ncrit to substantially alter the shape (intensity profile) of the critical angle transition 116. This is because location of the maximum intensity slope of the critical angle transition 116 is used to determine the stress-related parameters of the IOX article 10. A guided or leaky mode resonance that adversely affects the critical-angle intensity transition in the captured prism-coupling spectrum is referred to herein as an offending resonance or an offending mode.
As utilized herein, an optical propagation mode is referred to as “guided” or “bound” if its effective index is higher than the critical index. As utilized herein, an optical propagation mode is referred to as “leaky” if its effective index is lower than the critical index. A leaky mode produces a transmission resonance when its effective index is relatively close to the critical index, particularly if it is substantially closer to the mode spacing of the last two guided modes, i.e., the two guided modes with the lowest effective index for a particular polarization.
As utilized herein, the “transmission resonance” refers to a dip in the intensity in a given mode spectrum 113TM or 113TE where the intensity would normally monotonically decrease with decreasing effective index for neff<ncrit. When the dip in the mode spectrum gets very close to the critical-angle transition 116, the location of maximum slope shifts toward a slightly larger effective index, which corresponds to the lowest material index near the bottom of the spike region R1.
In a similar way, a guided mode with an effective index only slightly above the critical index may cause the intensity in the vicinity of the critical angle transition 116 to change due to the nonzero breadth of the coupling resonance for the mode. The nonzero breadth may be a result of several factors, including the coupling strength, the resolution of the optical system in the prism-coupling system 28, and aberrations caused by warp of the IOX article 10 in the measurement area.
In each of the above cases, the apparent location of the critical angle in the measured mode spectrum 113TM or 113TE is shifted significantly when the location of the corresponding resonance (bound-mode or leaky-mode resonance) is within a distance from the critical angle that is about the same as the breadth of the resonance in terms of effective index, or smaller.
Hence, a measured mode spectrum 113TM or 113TE may be considered outside of the preferred measurement window when a guided mode is within 0.5 FWHM, such as within 0.6 FWHM or 0.7 FWHM of the breadth of the guided-mode resonance. Similarly, a measured mode spectrum 113TM or 113TE is considered outside of the preferred measurement window when the lowest-intensity point of a leaky mode is within 0.5 FWHM, such as within 0.6 FWHM or 0.7 FWHM breadth of the leaky-mode resonance.
When the leaky-mode resonance is somewhat farther away from the critical index ncrit, the resonance is broad and asymmetric, and its FWHM may be challenging to measure and define in industrial measurement conditions. Hence, in some embodiments, a different criterion can be used to identify whether a given leaky mode adversely affects the critical angle transition 116. In one such method, the distance between the lowest-intensity point (the dip location) of the leaky mode and the apparent position of the critical angle transition 116 is considered.
The measured mode spectrum 113TM or 113TE may be considered within the preferred measurement window when the distance between the leaky mode dip location and the apparent location of the transition is smaller than 0.2 times the distance from the apparent critical angle transition to the nearest guided-mode location, or smaller than 0.3, 0.4, or 0.5 times the distance from the apparent critical-angle transition to the nearest guided-mode location. The choice of this distance depends at least in part on the shape of the spike region R1, and may be chosen based on empirical evidence from data collected on multiple IOX articles 10.
In another example, the determination of whether both the TM and TE mode spectra 113TM and 113TE are within a preferred measurement window is based on the relationship between the second derivative of the intensity profile of the nearest mode (fringe) to the critical index and the distance between this nearest mode and the apparent location of the critical angle transition 116. Qualitatively, the same method applies for analyzing this relationship for a bound mode and for a leaky mode, except that the decision threshold for a bound mode need not be the same as for a leaky mode.
In some embodiments, the distance between the offending mode and the apparent critical-angle transition 116 is compared to a numerical factor divided by the square root of the second derivative of the optical intensity at the mode location. This is based on the observation that the full width at half-maximum (FWHM) for many bell-shaped intensity distributions of resonant peaks of unit peak value is proportional to the inverse of the square root of the second derivative of the intensity at the location of the resonance (at the minimum for an intensity dip or at the maximum for an intensity peak).
For example, for a Lorentzian of unit peak value, the FWHM is about
for a Gaussian of unit-peak value it is about
and for a hyperbolic secant it is about
where I* stands for the second derivative of intensity with respect to the horizontal variable of the spectrum (for example, position, angle, effective index, or point number). In many cases, the apparent position of the critical-angle transition 116 is substantially unaffected by the nearby (nearest) mode if the distance between the transition and the nearby mode is larger than about 1.8 times the FWHM breadth of the resonance of the nearby mode.
In some embodiments, the measured mode spectrum 113TM or 113TE is considered outside the preferred measurement window when the distance between the location of a nearby mode and the (apparent) critical-angle transition 116 for the same polarization state is less than 1.8 times the FWHM breadth of the coupling resonance of the nearby mode.
In some embodiments, measured mode spectrum 113TM or 113TE is considered outside the preferred measurement window if it is within less than 1.5 times the FWHM breadth of the coupling resonance of said nearby mode, such as less than 1.2, less than 1, less than 0.8, less than 0.6, or less than 0.5 times the FWHM breadth of the coupling resonance of said nearby mode.
A preferred threshold ratio for the determining whether a measured mode spectrum 113TM or 113TE is inside or outside a preferred measurement window can be based on a trade-off between the importance of high precision for the measurement of the given stress parameter (e.g., knee stress CSk) and the importance of having a broad measurement window. Greater importance on measurement accuracy favors a larger ratio of the minimum acceptable spacing to the FWHM, and vice versa.
In addition, in cases where the shape of the intensity distribution corresponding to the given mode is well-described by a Lorentzian profile, a preferred threshold value of the ratio maybe higher, such as in the range of 0.8 to 1.8. In cases where the given mode is well-described by a Gaussian profile, the preferred threshold value of the ratio may be lower, such as in the range of 0.5 to 1.2.
Based on the above considerations, a measured mode spectrum 133TM or 113TE is deemed outside the preferred measurement window when the distance between the apparent position of the critical-angle transition 116 and the nearby offending mode is less than or equal to about
This is a relatively strict criterion used to ensure at most a negligible shift in the apparent position of the critical-angle transition 116. In various cases, of different line shapes and preferred trade-off between the target accuracy of the stress parameter in question (e.g., knee stress CSk) and breadth of the preferred measurement window, a less-strict threshold for the spacing maybe chosen. For example, the spacing may be less than or equal to a factor of 8.5, such as less than or equal to a factor of 6.8, 5.7, 4.5, 3.4, or 2.8 times
Furthermore, in some cases where the shape of the nearby mode resonance is far from Lorentzian, and closer to Gaussian, and a maximized breadth of the measurement window is a higher priority, the preferred threshold value of the spacing between the mode and the apparent transition position 116 may be less than or equal to 2.4, such as less than or equal to 1.9, 1.4, or 1.2 times
The second derivative at the location of the nearby mode may be found by smoothing of the signal by low-pass filtering, finding a first derivative digitally and smoothing it by low-pass filtering, then finding a second derivative digitally, smoothing it, and taking the value at the location of the mode resonance. In some embodiments, the second derivative may be found by fitting a parabola (second-order polynomial) to the signal in the closest vicinity of the mode location, and taking the second derivative of the fitting parabola to serve as the second derivative representing the coupling resonance of the mode. Such methods for finding the second derivative are known in the art.
Furthermore, in some embodiments, the intensity distribution in the vicinity of a mode resonance (guided or leaky mode) is normalized so that the minimum intensity corresponds to 0 and the maximum intensity corresponds to 1, or vice versa. In one example of a reflection mode spectrum where the maximum coupling on resonance with a guided or leaky mode corresponds to a local minimum in the reflected intensity, the minimum intensity at the bottom of the reflected-intensity dip may be subtracted from the entire intensity distribution so that a second intensity distribution has a minimum at 0. Then the second intensity distribution is multiplied by a scaling factor so that the maximum value in the vicinity of the local minimum becomes equal to 1. This provides a scaled normalized intensity distribution having a range from 0 to 1. The second-derivative may then be calculated after the normalization procedure.
If it is found that both of the measured TM and TE mode spectra 113TM and 113TE are in the preferred measurement window, then the knee stress CSk and related parameters (e.g., depth of spike D1, depth of layer DOL, etc.) can be determined using these mode spectra. Furthermore, if the TM mode spectrum 113TM is found to be within the preferred measurement window, it may be chosen to calculate the depth of layer DOL based on the TM fringe count only before deciding whether to determine the knee stress CSk using the same TM mode spectrum and the associated TE spectrum 113TE that was measured at the same time.
If it is found that one of the measured TM and TE mode spectra 113TM or 113TE resides outside of the preferred measurement window, then another (second) pair of TM and TE mode spectra 113TM or 113TE is considered. The second pair of mode spectra 113TM and 113TE may be collected after the determination was made that the at least one of the first TM and TE spectrum was not inside the preferred measurement window. Alternatively, the second pair of mode spectra 113TM and 113TE can be collected in advance using the prism-coupling system 28 set to different measurement conditions than used in obtaining the first pair of mode spectra.
In an example, the light source system 60 of the prism-coupling system 28 is adjusted so that the light 62 has a different wavelength for the second measurement than the first measurement. The second wavelength may be chosen to provide continuity of the preferred measurement window so that as an IOX article 10 that falls barely outside the preferred measurement window for the first wavelength falls inside the preferred measurement window for the second spectrum having a different wavelength.
For example, consider the IOX article formed from a Li-containing aluminosilicate glass-based substrate 20 and with a spike region R1 formed using a K+ IOX process. The measured mode spectrum 113TM or 113TE has full mode count between about 2.1 and about 3 fringes at a first measurement wavelength of 590 nm. The calculated surface compressive stress is the range of 500 to 900 MPa.
This particular example IOX article 10 can benefit from a second measurement of the mode spectra 113TM and 113TE using a second wavelength that is longer than the first wavelength by between about 1% and 15% to shift the fringe count range inside a preferred process (measurement) window having a range on the full mode count of 2.3 to 2.7.
Similarly, when a measured mode spectra 113TM or 113TE yield a mode count is just below the lower end of the preferred measurement window (for the present case, when the fringe count falls in the range 1.75-2.1 fringes), then the second wavelength may be made shorter by between about 1% and 25%, depending on how far the mode fringe count falls outside the preferred measurement window.
A more significant shift of the preferred measurement window can be used by making a larger wavelength shift, such as by 18%, 25%, or 30%. A larger shift in the measurement wavelength can be used to establish a larger measurement window by combining the measurement windows of two different measurement wavelengths.
In an example a condition where a spike requires a wavelength that is between two neighboring measurement wavelengths to fall inside the preferred measurement window is avoided. In an example, for a spike having a linear shape with surface index increment Δn above the base index n, the relationship between the fringe count N, the measurement wavelength λ, and the spike depth D1 or DOLsp is:
The difference in fringe count between the TM and the TE mode spectrum 113TM and 113TE depends on the difference in between the two mode spectra, since the other parameters that determine the fringe count are the same for the two polarization states in the measurement. If the surface compressive stress is labeled CS, and the knee stress is CSk, then the difference in between the two polarizations is approximately equal to (CS-CSk)/SOC, where SOC is the stress-optic coefficient. The SOC is typically within 15% of 3×10−6 RIU/MPa for most chemically strengthened glasses, where RIU stands for refractive-index units.
For a spike produced by an IOX process using K in a Na-based or Li-based glass substrate 20, the difference in Δn between TM and TE is usually about 1/5.6 of the average of the two Δn values. If the stress-induced birefringence of Δn is labeled δnTM-TE, then the difference in fringe count between the two polarizations is:
This means that the fringe count for the TE polarization state is typically about 10/11 of the fringe count of the TM polarization state. Therefore, the fringe count for TE is different by:
The factor of 0.09 relating the mode count difference to the TM mode count will vary slightly with variations in SOC, and is approximately proportional to the square root of the ratio of SOC to 3×10−6. For SOC ranging from about 2×10−6 to about 4.5×10−−6, the corresponding factor would vary from about 0.073 to about 0.11.
Having established that a preferred measurement window for each polarization has a fractional part FP of the fringe count between about 0.1 and 0.8, such as between about 0.15 and 0.75, a preferred measurement window for each polarization may span about 0.6 fringes. Given that there is an offset between the TM and the TE fringe count, the effective preferred measurement window for simultaneously having an accurate measurement of the critical index in the TM and the TE polarization is reduced compared to the single-polarization preferred measurement window by the difference in mode count between TM and TE.
In an example for a typical glass with 0.073NTM≤δNTM-TE≈0.11NTM, for a TM mode spectrum 113TM having about 2.6 TM fringes 115TM, the preferred measurement window is reduced from about 0.6 fringes for TM polarization alone to 0.6−(0.19 to 0.29)=(0.31 to 0.41) fringes. Similarly, for a target TM mode spectrum 113TM having 3.6 TM fringes 115TM, the preferred measurement window is reduced from about 0.6 to about 0.6−(0.26 to 0.40)=(0.2 to 0.34) fringes. In the former case, the reduction is between about ⅓ and ½, depending on the value of SOC, while in the latter case the reduction is approximately from about ½ to about ⅔ of the single-polarization preferred window. Thus, the offset in fringe count between TM and TE mode spectra 113TM and 113TE substantially reduces the effective breadth of the continuous process window available within a single preferred measurement window.
In some embodiments where the first TM or TE spectrum 113TM or 113TE measured at a first measurement wavelength fails to fall inside the preferred measurement window, then a mode spectrum measured at a different (second) measurement wavelength is used to position the TM and the TE spectrum inside the preferred measurement window. If the mode spectrum having a larger fringe count (usually the TM spectrum 113TM) has between about 2.75 and 3.15 fringes, then the measurement wavelength may be increased to bring the fringe count for the TM spectrum in the preferred range 2.15-2.75.
To shift the entire uncovered range 2.75-3.15 fringes to the preferred measurement window 2.15-2.75 fringes using a single longer wavelength, it may be preferred that the single longer second wavelength be at least 12% longer than the first measurement wavelength, preferably 14% longer or more.
On the other hand, it may be desirable to ensure continuity of the measurement so that no IOX article that at the first measurement wavelength has between 2.75 and 3.15 fringes in the polarization state with higher fringe count also falls outside the preferred measurement window at the second (longer) wavelength. Thus, for the longer second measurement wavelength, it may be preferred that the fringe count in the other polarization state does not fall out of the preferred measurement window. In the present example, the change in wavelength is used to shift the mode count from the range 2.15-2.75 fringes to below about 2.1 fringes.
In an example, the higher-fringe-count polarization may have 2.6-2.75 fringes at the first wavelength, and the lower-fringe-count polarization may have 2.35-2.55 fringes for a typical glass with SOC of about
Then, for the example with a lower fringe count of 2.35, a wavelength increase beyond 12% would cause said lower fringe count to drop below 2.1, falling out of the preferred measurement window.
On the other hand, for a mode fringe count of 2.55, a wavelength increase of up to 19.6% would retain the corresponding mode spectrum within the extended preferred measurement window of 2.1-2.8 fringes. Hence, for a typical glass substrate, it is preferred that the wavelength change for the second wavelength not exceed 20% of the first wavelength, such as not exceed 12% of the first wavelength.
In some embodiments, it is preferable that a continuous capability of measuring an IOX article 10 inside a preferred measurement window available among the two or more wavelengths instead of gaining the maximum possible extension of the preferred measurement window by covering the entire problematic range of 2.75-3.15 fringes by switching to the longer wavelength. Hence, having a wavelength increase exceeding 12% or 14% of the first wavelength can be desirable but may not be required or strongly preferred. On the other hand, having a wavelength increase below 20% for some glasses or below 12% for most glasses may be strongly preferred to enable continuous availability of a preferred measurement window among a large variety of IOX articles 10 centered around a target measurement spectrum with 2.1-2.8 fringes. There are less common glasses with a SOC that is substantially lower, such as in the range
for which significantly larger wavelength increase is possible without falling out of the preferred measurement window for the polarization having the lower fringe count.
Examples of preferred wavelength changes for 4 different values of the stress-optic coefficient measured in Brewsters, or B
are given in Tables 1 through 4, below. These examples are given for the case where the preferred change is to increase the wavelength because the larger of the two fringe counts is exceeding the upper end of the measurement window. When the smaller fringe count falls below the bottom of the preferred measurement window, the preferred change is to a shorter wavelength, and similar wavelength percentage changes would be preferable as in the examples of Tables 1 through 4.
Table 1 provides the preferred wavelength change for measurement windows with different fringe counts, for a material with a SOC of about 1 B.
Table 2 provides the preferred wavelength change for measurement windows with different fringe counts, for a material with SOC of about 2 B.
Table 3 provides the preferred wavelength change for measurement windows with different fringe counts, for a material with SOC of about 3 B.
Table 4 provides the preferred wavelength change for measurement windows with different fringe counts, for a material with SOC of about 4 B.
The examples in Tables 1 through 4 demonstrate that in some cases it can be advantageous to change the wavelength up to about 28% of the first measurement wavelength. In many cases, the main benefits can be obtained with significantly smaller wavelength changes, e.g., in the range of 8-24%. Mode spectra containing more fringes per polarization state require smaller wavelength shifts to achieve simultaneous preferred-window condition for both wavelengths. For such cases, several discrete wavelengths (3 or more) may be required to provide a wide enough fabrication window with continuous accurate quality control measurement coverage.
Example IOX Article
In one example, an IOX article 10 was formed from a glass substrate 20 having the composition 63.16 mol % SiO2, 2.37 mol % B2O3, 15.05 mol % Al2O3, 9.24 mol % Na2O, 5.88 mol % Li2O, 1.18 mol % ZnO, 0.05 mol % SnO2, and 2.47 mol % P2O5, and a SOC of about 3B. A DIOX process for chemical strengthening was employed. After a first K+-L+ IOX step (i.e. with r as the in-diffusing ion 11), the TM and TE mode spectra 115TM and 115TE each had between 2 and 3 fringes at a first measurement wavelength λ=590 nm. After a second IOX step, the TM and TE mode spectra 115TM and 115TE each had between 3 and 4 fringes at 590 nm. The surface stress CS associated with the formation of the K+-based spike region R1 is usually in the range 500 to 640 MPa. The surface stress CS after the second IOX step using Na+ as the in-diffusing ion 12 is typically in the range 750-950 MPa.
Using the methods described herein, the measurement requirements for both step 1 and step 2 can be fully met with a continuous effective preferred measurement window when using three measurement wavelength windows centered around the measurement wavelengths λ of 545 nm, 590 nm, and 640 nm, respectively. Furthermore, in an example it is preferred that the spectral bandwidth of the measurement light 62 not exceed about 8 nm, 9 nm, and 10 nm, respectively, at these measurement wavelengths. For even higher fringe contrast, the spectral bandwidths can be limited to 4 nm, 5 nm, and 6 nm, respectively. Thus, in one example, each measurement wavelength has a spectral band of 10 nm or less, or in another example, of 6 nm or less.
When the fringe count is close to either edge of the 590 nm measurement window after step 2, the mode spectrum is brought back inside the preferred measurement window by either increasing or decreasing the measurement wavelength, depending on whether the upper or the lower end of the measurement window approaches at 590 nm. In another example using a three measurement wavelength implementation, the shortest measurement wavelength is about 540 nm, the middle measurement wavelength is about 595 nm, and the longest measurement wavelength is about 650 nm.
While two or three measurement wavelengths have been discussed above by way of example, any reasonable number of measurement wavelengths may be used. For example, using two measurement wavelengths can increase the measurement window by up to a factor of 2, and may be quite adequate to satisfy the needs for a reasonable fabrication process window. On the other hand, in some cases where the spike depth D1 is relatively is large and produces several (e.g., 3, 4, or more) fringes per polarization state, or when the SOC is very high such as 4 B, more than three wavelengths may be preferred. The multiple measurement wavelengths can be positioned closer together than in the three wavelength examples above, e.g., spaced by 7.6% and 9.2%, respectively, of the average wavelength which in these examples is the middle of the three measurement wavelengths.
An exemplary method suppresses systematic errors in the measurement of the knee stress CSk and in the measurement of the depth of the spike DOLsp. The suppression of systematic errors may be essentially complete when the multiple measurement wavelengths are carefully chosen to be close enough to allow a seamless transition between preferred measurement windows at the different wavelengths. This means that the preferred measurement windows at neighboring wavelengths can overlap at least slightly.
The examples listed in Tables 1 through 4 allow selecting preferable wavelength shifts that guarantee such overlap and measurements that are substantially free of systematic errors for a range of samples that may cover a continuous range of fabrication conditions. On the other hand, when the wavelengths are spaced slightly more than the preferred spacing that guarantees window overlap, a maximum expansion of measurement capability is obtained, but at the expense of only partial suppressing systematic errors. The possibility still exists that certain IOX articles 10 can show deviations from accurate measurement, even though the probability of having such samples decreases due to the much increased coverage of the production range with multiple preferred measurement windows.
In some embodiments, the corrective action taken when at least one of the TM and TE spectra 113TM and 113TE is/are not in the preferred measurement window includes changing the thickness of the interfacing fluid 52 (e.g., index oil) to help bring the problematic spectrum inside a preferred measurement window. This is possible because the interfacing fluid can be considered part of the waveguide 26. The main problem that is solved with this corrective action is to determine the knee stress CSk correctly, i.e., to within select tolerance. The preferred refractive index of the interfacing fluid 52 at the measurement wavelength is higher than the critical index for the polarization state in which the problematic spectrum occurs. Furthermore, the preferred refractive index of the interfacing fluid 52 is higher than the critical index by no more than 0.1, such as by no more than about 0.06, or by no more than 0.04. In some embodiments, the interfacing fluid 52 can be selected to have a refractive index as close as possible to the expected refractive index on the surface of the glass (e.g., the surface refractive index of the potassium spike).
In particular, the interfacing fluid refractive index nf may be within about 0.004 or 0.003 of the surface refractive index no. The surface refractive index n0 is usually different for TM and TE polarizations due to the significant surface stress in the spike, but the difference is usually less than 0.004, and most often less than 0.003. As noted above, the interfacing fluid 52 resides between the prism coupling surface 44 of the coupling prism 40 and the surface 12 of the IOX article 10, and the thickness TH of the interfacing fluid can be controlled using the vacuum system 56. Initially, the amount vacuum can be relatively high, making the thickness TH of the interfacing fluid 52 relatively small, e.g., 200 nm or less, or even 100 nm or less. With this thickness TH of the interfacing fluid 52, the surface compressive stress CS and the spike depth D1 can be measured with adequate accuracy. The spike depth D1 may be over-estimated by as much as 0.1 microns, or even 0.2 microns, which may be acceptable in many cases. The surface compressive stress CS may be slightly under-estimated by assuming that the interfacing fluid thickness is 0 when in fact it might be as high as 0.1 or even 0.2 microns.
In an example, the thickness TH of the interfacing fluid 52 is adjusted in a way that it increases the effective index of a leaky mode to turn it to a quasi-guided mode of the waveguide 26, wherein a quasi-guided mode has an effective index higher than that of the index corresponding to the critical-angle transition.
In another example, thickness TH of the interfacing fluid 52 is adjusted in a way that increases the effective index of a leaky mode to turn it to a quasi-guided mode the waveguide 26 so that fractional part FP of the new mode count now falls in the preferred (extended) measurement window MWE, wherein the refractive index of the interfacing fluid may be higher than the refractive index corresponding to the critical angle.
In another example, the thickness TH of the interfacing fluid 52 is adjusted to decrease the effective index of a leaky mode to turn it into a quasi-guided mode of the waveguide 26 so that fractional part FP of the new mode (fringe) count now falls in the preferred measurement window MWE. In this case, the index of the interfacing fluid 52 may be lower than the index corresponding to said critical angle.
Another example includes changing the refractive index of the interfacing fluid 52 to change the effective index of the leaky mode to turn it to a quasi-guided mode having an effective index higher than the critical-angle effective index. The example can also include changing the fractional part FP of the fringe count so that the fractional part FP falls within a fractional-part range associated with the preferred measurement window. In the description herein, changing the refractive index of the interfacing fluid 52 includes replacing at least a portion of a first interfacing fluid having a first refractive index with a second interfacing fluid having a second refractive index. This process can be used to define essentially any refractive index between the first refractive index and the second refractive index.
Once the prism-coupling system 28 is placed in the desired configuration and the mode spectrum 113 collected, the CS and DOL values are then recorded. If both the TM and the TE mode spectra 113TM and 113TE fall within in the preferred measurement window as described above, then the TM and TE critical index ncrit is measured by the location of the highest slope in the intensity profiles of the respective critical angle transitions 116. This provides a measure of the birefringence, which is used to calculate the knee stress CSk.
On the other hand, if at least one of the TM or TE mode spectra 115TM and 115TE is not in the preferred measurement window, then a leaky or a guided mode in the problematic TM or TE mode spectrum may be offending, i.e., has an effective index too close to the critical index and adversely affects the apparent location of the critical-angle transition 116. At this point, the thickness TH of the interfacing fluid 52 can be increased, e.g., by decreasing the vacuum (e.g., increasing the pressure) until the effective index of the problematic leaky or guided mode increases enough to be non-offending, i.e., becomes far enough above the critical index that the critical-angle transition 116 is substantially undisturbed and the critical angle (and hence the critical index) for the given polarization can be accurately measured.
It would be preferred that the critical angles for both the TM and TE polarizations be measured at the same time, but this is not required. If the first measured mode spectrum for the other polarization state was in the preferred measurement window before taking the corrective action, it is possible to measure the CSk by using the measured critical-angle position for the other polarization state using the original thickness of the index-matching fluid 52. Choosing to take both measurements of the TM and TE mode spectra 113TM and 113 TE at the same time helps avoid errors from slight changes in the prism-coupling system 28 that can occur over time.
Experimental Results
An initial (“original”) measurement window MWO for the single-wavelength measurement method is depicted with long-dash lines, while an extended (preferred) measurement window MWE for the three-wavelength measurement methods and prism-coupling systems as described herein is shown with short-dash lines. The extended measurement window MWE that uses three measurement wavelengths λ is significantly extended as compared to the single-wavelength measurement window MWO. Since the IOX process time defines the refractive index profile of the IOX article 10, an extended measurement window MWE having a wider range of IOX process times means IOX articles with a larger range of spike-based refractive index profiles can be characterized for at least one stress characteristic such as the knee stress CSk.
Frangibility
Frangible behavior or “frangibility” refers to specific fracture behavior when a glass-based article is subjected to an impact or insult. As utilized herein, a glass-based article (and in particular, a glass-based IOX article 10 such as considered herein) is considered non-frangible when it exhibits at least one of the following in a test area as the result of a frangibility test: (1) four or less fragments with a largest dimension of at least 1 mm, and/or (2) the number of bifurcations is less than or equal to the number of crack branches. The fragments, bifurcations, and crack branches are counted based on any 2 inch by 2 inch square centered on the impact point. Thus, a glass-based article is considered non-frangible if it meets one or both of tests (1) and (2) for any 2 inch by 2 inch square centered on the impact point where the breakage is created according to the procedure described below. In various examples, the chemically strengthened IOX article 10 can be frangible or non-frangible.
In a frangibility test, an impact probe is brought into contact with the glass-based article, with the depth to which the impact probe extends into the glass-based article increasing in successive contact iterations. The step-wise increase in depth of the impact probe allows the flaw produced by the impact probe to reach the tension region while preventing the application of excessive external force that would prevent the accurate determination of the frangible behavior of the glass. In one embodiment, the depth of the impact probe in the glass may increase by about 5 μm in each iteration, with the impact probe being removed from contact with the glass between each iteration. The test area is any 2 inch by 2 inch square centered at the impact point.
While coatings, adhesive layers, and the like may be used in conjunction with the strengthened glass articles described herein, such external restraints are not used in determining the frangibility or frangible behavior of the glass-based articles. In some embodiments, a film that does not impact the fracture behavior of the glass-based article 10 may be applied to the glass-based article prior to the frangibility test to prevent the ejection of fragments from the glass article, increasing safety for the person performing the test.
In the frangibility test described herein, the impact is delivered to the surface of the glass-based article with a force that is just sufficient to release the internally stored energy present within the strengthened glass-based article. That is, the point impact force is sufficient to create at least one new crack at the surface of the strengthened glass-based article and extend the crack through the compressive stress CS region (i.e., depth of layer) into the region that is under central tension CT.
It will be apparent to those skilled in the art that various modifications to the preferred embodiments of the disclosure as described herein can be made without departing from the spirit or scope of the disclosure as defined in the appended claims. Thus, the disclosure covers the modifications and variations provided they come within the scope of the appended claims and the equivalents thereto.
This application claims the benefit of priority of U.S. Provisional Application Ser. No. 62/940,295 filed on Nov. 26, 2019 the content of which is relied upon and incorporated herein by reference in its entirety. The present disclosure relates to prism-coupling systems and methods used for characterizing stress in glass-based chemically strengthened articles, and in particular relates to such systems and methods having multiple light sources with different wavelengths.
| Number | Date | Country | |
|---|---|---|---|
| 62940295 | Nov 2019 | US |
