Patent Application
20240426594
This technology generally relates to systems and methods for interferometrically measuring the displacement of a surface with high accuracy even when the surface is sloped or tilted.
Areal surface interferometry, including areal phase-measuring interferometry, has been used to measure the shape or form of optical surfaces for several decades. While generally quite fast and accurate, prior art areal surface interferometry suffers from errors—such as retrace errors, errors associated with non-ideal phase shifting, errors caused by the environment including temperature gradients, pressure gradients, humidity gradients, and even CO2 gradients, errors arising from uncertainties associated with the wavelength of the measurement light, errors caused by vibration, and errors caused by electron, photon, and detection noise—and also introduces unexpected costs and complexities in the surface metrology process.
Further, areal interferometers often depend on test spheres and null correctors, and an error in their fabrication or installation can result in later errors in the surface topography measurement results. In this example, the infamous surface errors in the primary mirror of the Hubble Space Telescope have been traced to problems with a null corrector. Since that time NASA—and associated manufacturers of large optics—have been seeking non-areal yet non-contact approaches for high-precision surface metrology. Generally, these approaches have entailed the use of an optical probe system that measures displacement of a surface at a given location, and the probe is then scanned across the surface of interest to generate a complete topographic profile of the surface of the optic.
One such prior art displacement measuring device is the spectral interferometric probe 10 shown in
The two re-collimated light beams then pass through the beamsplitter 16, enter the focusing lens 40, and then enter the spectrograph 42 through a small aperture at the focal point of the focusing lens 40. The two re-collimated beams then form a spectral interference pattern on the image sensor of the camera 44 associated with the spectrograph 42. The resulting spectral interference fringe pattern has several inflection points and high-slope regions for improved downstream processing and fitting by the digital processor 46.
Under these conditions, the displacement can be found quite accurately, to less than a nanometer, and is a particular strength of the spectral interferometric probe 10. A second strength is that if the measurement light reflected from the test surface 32 is weak (perhaps because the test surface 32 is highly polished and slightly tilted) then the interferometric gain present in the interference pattern provides a means of intensifying the weak optical signal so that it is of sufficient brightness to be image-able by the spectrograph 42 and to be processed by the digital processor 46.
Unfortunately, a serious drawback of the spectral interferometric probe 10 is that the optical path lengths of the reference arm and the measurement arm in this example are substantially unequal in order to obtain interference fringes at the image sensor of the camera 44. Since the optical path length, or equivalently the displacement, associated with the test surface 32 is unknown, then the position of the reference mirror 24 in this example is scanned, or equivalently, the reference arm is not scanned and instead the whole measurement head 20 is scanned by virtue of PZT 22 until a scanning position is found that produces the desired interference fringes in spectrograph 42. This scanning process requires a significant amount of time and limits the measurement throughput rate of spectral interferometer probe 10 to about 100 displacement measurement per second.
An additional limitation of interferometric probe 10 is the inability to measure the topography of surfaces that are sloped more than a few degrees with respect to the optical axis 18 of the interferometric probe 10. Light reflected from such a tilted test surface will not propagate back through the optical train of interferometric probe 10 and enter the spectrograph 42 and therefore will not produce optical signals that can be analyzed and therefore a displacement to test surface 32 cannot be determined.
An interferometer comprises an optical axis, a reference arm comprising at least a concave mirror substantially centered on the optical axis, a measurement arm comprising at least a concave mirror substantially centered on the optical axis, a test surface, an input/output arm comprising a fiber optic substantially centered on the optical axis, a convex mirror substantially centered on the optical axis, and a plurality of light detecting devices. The convex mirror is configured to receive diverging light from the fiber optic of the input/output arm and reflect a portion of that light into the measurement arm in a manner such that light reflected from the concave mirror of the measurement arm is brought to a focus at the surface under test. Light reflected from the test surface is incident upon the concave mirror of the measurement arm which directs the light to the convex mirror which in turn reflects and focuses the measurement light onto the fiber optic of the input/output arm of the interferometer. The convex mirror is also configured to receive diverging light from the fiber optic of the input/output arm and reflect a portion of that light into the reference arm in a manner such that light reflected from the concave mirror of the reference arm is reflected again from the convex mirror and brought to a focus at the fiber optic of the input/output arm. The interferometer can also comprise a spider or other support structure that mounts and locates the fiber optic of the input/output arm in place with respect to the location of the other optical elements of the interferometer. The interferometer can also comprise a spider or other support structure that mounts and locates the convex mirror in place with respect to the location of the other optical elements of the interferometer. Further, light detectors can be installed on one or more arms of the support structure and configured to detect a tilt of the test surface with respect to the optical axis.
An interferometer system comprising the afore-described interferometer, a broadband light source, a fiber optic light delivery system that transports light from the broadband light source to the interferometer, a spectrometer that detects and spectrally disperses light output by the interferometer, a fiber optic light delivery system that transports light from the interferometer to the spectrometer, an electronic camera that captures images of the spectral interferogram produced by the spectrometer, a data acquisition sub-system that collects light intensity data from the tilt-detecting light detectors, and a digital processing system that processes the spectral interferogram and the acquired tilt data to compute a highly accurate distance measurement to the test surface.
Accordingly, examples of the claimed technology provide a number of advantages including measurement operations that do not require the mechanical movement of a reference mirror or an interferometer head to perform a displacement measurement such that the measurement system has a fast displacement measurement rate, as well as the high accuracy of an interferometric probe even when the surface being measured is sloped or tilted.
An interferometer 100 in accordance with examples of the claimed technology is illustrated in
Continuing with reference to
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Fiber spider support structure 118 is a mechanical device comprising several arms emanating from a central lobe that is used to hold the input/output optical fiber 128 in place with respect to housing 102, reference mirror 104, primary mirror 108 and secondary mirror 114. Note that input/output optical fiber 128 can be installed in a hole in the central lobe of fiber spider support structure 118 that is substantially coaxial with optical axis 130, and the distal ends of the arms of fiber spider support structure 118 can in turn be coupled to housing 102. In this example, Fiber spider support structure 118 can have between two and ten arms (fiber spider support structure 118 shown in the figures have five arms), and fiber spider support structure 118 can be installed proximal to the rear-side of primary mirror 108 (i.e., not on the side of primary mirror 108 having primary mirror surface 110) so the arms of fiber spider support structure do not have the opportunity to block light incident onto—or reflected from—primary mirror surface 110). In this example, the fiber spider support structure 118 can comprise a polymer, glasseous, ceramic, or metallic material, but is preferentially composed of a material that is rigid and has a low CTE such as ULE, Zerodur, or Invar, and is even more preferentially composed of the same material that housing 102 is composed of. In this example, the arms of fiber spider support structure 118 can be thin so as to not block light propagating to or reflected from reference mirror 104, the width of the arms being less than 2.0 mm, or preferably less than 1.0 mm. The arms of fiber spider support structure 118 must be of sufficient length to reach the inner side-wall of housing 102.
Secondary spider support structure 120 is a mechanical device comprising of several arms emanating from a central lobe that is used to hold the secondary mirror 114 in place with respect to housing 102, input/out fiber 128, reference mirror 104, and primary mirror 108. Note that secondary mirror 114 can be installed in a hole or recess at or in the central lobe of secondary spider support structure 120 that is substantially coaxial with optical axis 130, and the distal ends of the arms of secondary spider support structure 120 are in turn coupled to housing 102. Secondary spider support structure 120 can have between two and ten arms (secondary mirror spider support structure 120 shown in the figures has five arms). In this example, preferably, secondary spider support structure 120 has the same number of arms as fiber spider support structure 118, the width of the arms of secondary spider support structure 120 is the same as the width of the fiber spider support structure 118, and the angular orientation of secondary spider support structure 120 about optical axis 130 is the same as the angular orientation of fiber spider support structure 118 about optical axis 130. In this example, secondary spider support structure 120 can comprise a polymer, glasseous, ceramic, or metallic material, but is preferentially composed of a material that is rigid and has a low CTE such as ULE, Zerodur, or Invar, and is even more preferentially composed of the same material that housing 102 is composed of. In this example, the arms of secondary spider support structure 120 can be thin so as to not block large amounts of light propagating to or reflected from primary mirror 108, the width of the arms being less than 2.0 mm, or preferably less than 1.0 mm. The arms of primary spider support structure 118 must be of sufficient length to reach the inner side-wall of housing 102.
Continuing with reference to
Input/output optical fiber 128 is an optical fiber through which is delivered into interferometer 100 broadband light from a broadband light source, and through which light exits from interferometer 100 and is delivered to an optical analyzer such as a spectrometer. In this example, the input/output optical fiber 128 can be a multi-mode fiber but is preferentially a single-mode fiber having a core 6 μm's or less in diameter. In this example, the outer diameter of the jacket of input/output optical fiber 128 can be less than or equal to 3.0 mm, but is preferentially less than 1.00 mm, or more preferentially less than 0.50 mm to minimize the amount of light propagating within interferometer 100 that is blocked by input/output optical fiber 128. In this example, the input/output optical fiber 128 is transmissive to those wavelengths of light that interferometer 100 uses such as from 500 nm to 600 nm, or more preferably from 450 nm to 700 nm, or even more preferably from 400 nm to 800 nm. A good candidate fiber for use as input/output optical fiber 128 is the SM450 fiber from Thorlabs (Newton, NJ, USA) which has an outer jacket or cladding diameter of 0.245 mm and is highly transmissive from 488 nm to 633 nm but nonetheless has adequate light transmissivity from 430 nm to 800 nm wavelengths for use with interferometer 100.
Test surface 140 is that surface that is provided by the user whose topography is to be measured by interferometer system 300 wherein the topographical data can comprise a series or an array of individual displacement measurements. The displacement can be defined as that distance along optical axis 130 from measurement spot 138 on test surface 140 to a suitable, yet somewhat arbitrary, point on optical axis 130 such as, for example, where optical axis 130 intersect the apex of secondary mirror surface 116 or, for example, where optical axis 130 intersects the aperture of input/output optical fiber 128. Since what is generally desired as an output from interferometer system 300 is the change in displacement as interferometer 100 is scanned over test surface 140, the actual displacement end-point within interferometer 100 is arbitrary, although it must not change during the scanning and measurement processes. Alternately, interferometer 100 with interferometer system 300 can compute optical path differences (OPD) between the reference arm of interferometer 100 and measurement arm of interferometer 100 in which case the OPD indicates changes in displacement (substantially equal to two times the changes displacement) as the interferometer is scanned in which case no end-point within interferometer 100 is utilized.
In operation, interferometer 100 is scanned or translated across test surface 140 in a linear, curved, piecewise-linear, or areal pattern such that interferometer 100 can measure the displacement to test surface 140 in more than one location so the relative displacement between the two or more locations can be determined. Test surface 140 is generally a surface of an article of manufacture such as an optical surface such as, for example, the surface of a mirror, a window, or a lens. Test surface 140 can be substantially planar, or curved such as spherical, aspherical, free-form, cylindrical, acylindrical, parabolic, or even elliptical in shape. Test surface 140 can have a width as small as 0.5 mm or a width of up to 5000 mm or more. Test surface 140 can have a sag, or a range of displacement, of from less than 2 nanometers up to 1000 millimeters. The perimeter shape of test surface 140 can be substantially circular, elliptical, square, rectangular, or polygonal. Test surface 140 can be reflective having a reflectivity (to a certain band of wavelengths) greater than 90%, or absorptive such that 90% or more of the light incident upon it (within a certain band of wavelengths) is absorbed, or transmissive in which more than 50% of the light incident upon it (within a certain band of wavelengths) passes through test surface 140. In this example, test surface 140 can be specularly reflective and accordingly be highly polished, or test surface 140 can have a slight texture and if textured the standard deviation of the width of the features of the texture is preferably less than half the width of measurement spot 138 on test surface 140. Finally test surface 140 can be substantially perpendicular to optical axis 130 at measurement spot 138 or test surface 140 can be tilted with respect to optical axis 130, the amount of tilt being less than 5°, or up to 10°, or even 20° or more, although greater amounts of tilt have corresponding less amounts of light throughput through the measurement arm of interferometer 100.
Interferometer 100, like most interferometers, can be described as having four arms: a source arm, a reference arm, a measurement arm, and an output arm, some of which overlap or even share the same components in interferometer 100. The source arm of interferometer 100 is that arm that sources light into interferometer 100 and includes input/output optical fiber 128 and secondary mirror surface 116. The reference arm of interferometer 100 is that arm that provides reference light to interfere with light from the measurement arm and includes secondary mirror surface 116 and reference mirror surface 106 of reference mirror 104. The measurement arm of interferometer 100 is that arm that provides measurement light to interfere with light from the reference arm and includes secondary mirror surface 116, primary mirror surface 110 of primary mirror 108, and test surface 140. The output arm of interferometer 100 is that arm that outputs light from interferometer 100 and includes input/output optical fiber 128 and secondary mirror surface 116 of secondary mirror 114.
The prescription of a first exemplary configuration of the optics of interferometer 100 is presented in
In this example, the combined surface figure errors of reference mirror surface 106 and primary mirror surface 110 should be significantly less than the wavelength of light to ensure good contrast of the resulting spectral interference fringes in spectrograph 320; the figure error of reference mirror surface 106 can be less than 0.5 microns RMS, or preferably less than 100 nanometers RMS over the clear aperture of reference mirror surface 106. Likewise, in this example the surface figure error of primary mirror surface 110 can be less than 0.5 microns RMS, or preferably less than 100 nanometers RMS over the clear aperture of primary mirror surface 110.
The reflective coating of reference mirror surface 106, primary mirror surface 110, and secondary mirror surface 116 can comprise a metal such as aluminum, chromium, silver, gold, or even silicon, and can have a thin transparent protective coating, such as silicon dioxide, installed atop the reflective coating. In this example, the reflective coating of reference mirror surface 106 can preferably have substantially the same spectral reflectance properties as the reflective coating of primary mirror surface 110, or the reflective coating of reference mirror surface 106 can be less reflective than the reflective coating of primary mirror surface 110 such that after accounting for the reflectivity of the test surface 140 the intensity of the measurement light entering the input/output optical fiber 128 is approximately the same intensity (i.e., within 20% of one another) as the reference light entering the input/output optical fiber 128.
In this first example, the CTE of the material of housing 102 should be less than 10 parts per billion (PPB) per degree C., or preferably less than 5 PPB, or more preferably the CTE of the material of housing 102 is less than 2 PPB. As an example, if the reference arm temperature changes by 0.1 degrees C., the optical path length of the reference arm is 200 mm, and the CTE of the material of housing 102 is 10 parts per billion (PPB) per degree C., then the optical path length of the reference arm will change by 2×10−10 meters or 200 picometers—an amount much greater than the potential measurement accuracy of the present invention.
The method by which reference mirror 104, primary mirror 108, and even secondary spider support structure 120, secondary mirror 114, and fiber spider support structure 118 are bonded or attached to housing 102 should also not cause temperature-induced stresses and strains which can cause nanometer-scale movements, or even sub-nanometer scale movements, of the components with respect to one another. For example, if the optical components are all fabricated from ULE, then an organic UV glue or metallic or polymeric fasteners should not be employed to fasten the components together. In this example, a more preferable way to join the optical components of interferometer 100 together is to fabricate housing 102, reference mirror 104, primary mirror 108, secondary spider support structure 120, secondary mirror 114, fiber spider support structure 118 from ULE (or Zerodur) and then use a mixture of water, sodium hydroxide, and sodium silicate to bond the components together. With this process, known at times as hydroxide catalysis bonding (HCB), it is known that when the water evaporates, the sodium hydroxide and sodium silicate cause the glasseous optical components to chemically combine with one another such that they in effect become a unitary glass object. The resulting unitary glass object has substantially the same optical, thermal, and mechanical properties as the original glass of which the bonded components are composed.
With reference to
Source light within fiber light cone 150 that is incident upon secondary mirror surface 116 then reflects from secondary mirror surface 116 in accordance with the Law of Reflection into an outer portion primary light bundle 152 (as seen in
As mentioned above, source light within fiber light cone 150 that is incident upon secondary mirror surface 116 then reflects from secondary mirror surface 116 in accordance with the Law of Reflection into an outer portion primary light bundle 152 and an inner portion reference light bundle within reference light bundle 180. Continuing with reference to
A portion of the light of measurement spot 138 is reflected, in accordance with the Law of Reflection, from test surface 140 into reflected test light 170. If test surface 140 is substantially perpendicular to optical axis 130 then reflected test light 170, like test light 168, can have symmetry about optical axis 130, and occupy similar, if not substantially identical, overlapping spatial envelopes between test surface 140 and primary mirror surface 110. If test surface 140 is not perpendicular to optical axis 130 then reflected measurement light will not have symmetry about optical axis 130. In either case, small portions of reflected test light 170 will be incident on photodetectors 122 on the underside of secondary spider support structure 120, and photodetectors 122 are configured as part of a sub-system used to determine the tilt of test surface 140 such that retrace errors associated with interferometer 100 can be removed as described below.
That portion of reflected test light 170 that is not incident on one of photodetectors 122 nor incident on secondary spider support structure 120 can be incident on primary mirror surface 110, and subsequently reflect from primary mirror surface 110 in accordance with the Law of Reflection into returned measurement light 166. If test surface 140 is substantially perpendicular to optical axis 130 then returned measurement light 166, like measurement light 164, can have symmetry about optical axis 130, and occupy similar, if not substantially identical, overlapping spatial envelopes between primary mirror surface 110 and secondary mirror surface 116. If test surface 140 is not perpendicular to optical axis 130 then returned measurement light 166 will not have symmetry about optical axis 130.
A portion of returned measurement light 166 can then be incident on secondary mirror surface 116 and reflect from secondary mirror surface 116 into entering fiber light 174 in accordance with the Law of Reflection. If test surface 140 is substantially perpendicular to optical axis 130 then entering fiber light 174, like exiting fiber light 172, can have symmetry about optical axis 130, and occupy similar, if not substantially identical, overlapping spatial envelopes between input/output optical fiber optic 128 and secondary mirror surface 116. If test surface 140 is not perpendicular to optical axis 130 then entering fiber light 174 will not have symmetry about optical axis 130.
For the present invention the value of the magnification, hereinafter referred to as “M”, can be between 0.1 and 10.0, but for exemplary purposes will have a value of 2.0 (meaning the measurement arm is twice as long as the source arm and the diameter of measurement spot 138 is twice the diameter of the aperture of input/output optical fiber 128). In the following calculations the length of the measurement arm will be referred to as the Measurement Arm Length, or “MAL”, and the length of the source arm will be referred to as the Source Arm Length, or “SAL”. The value of SAL can be between 5 mm and 500 mm but will have an illustrative value of 50 mm. The value of MAL can be between 5 mm and 1000 mm but will have an illustrative value of 125 mm. In this example, therefore, the magnification M is 2.5.
The reflective surfaces comprising interferometer 100, namely secondary mirror surface 116, reference mirror surface 106, and primary mirror surface 110, can and will have subtle manufacturing flaws that result in surface topographies that differ somewhat, and generally uncontrollably, from the ideal or as-designed surface prescription. These surface figure errors can be less than 1.0 μm peak-to-valley, or preferably less than 0.10 μm peak-to-valley. These surface figure errors can cause spurious variations in OPL (optical path length) and OPD (optical path difference which is the difference in optical path length between the measurement and reference arms of interferometer 100) which can limit the accuracy of the displacement measurements of interferometer 100 to approximately the amount of the OPD variation. Further complicating matters is that, since the three reflective surfaces will generally not have perfect rotational symmetry due to the manufacturing errors, then the amount of OPD error will be a strong function of the tilt of test surface 140 with respect to optical axis 130.
Photodetectors 122 (e.g., photodetectors 122A through 122E) are provided and configured to detect shifts in the intensity of reflected test light 170 associated with tilts of test surface 140 as seen in
A second example of an interferometer 200 in accordance with examples of the claimed technology is illustrated in
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Input/output optical fiber 228 is an optical fiber through which is delivered into interferometer 200 broadband light from a broadband light source, and through which light exits from interferometer 200 and is delivered to an optical analyzer such as a spectrometer. In this example, the input/output optical fiber 228 can be a multi-mode fiber but is preferentially a single-mode fiber having a core 6 μm's or less in diameter. In this example, the outer diameter of the jacket of input/output optical fiber 228 can be less than or equal to 3.0 mm. In this example, the input/output optical fiber 228 is transmissive to those wavelengths of light that interferometer 200 uses such as from 500 nm to 600 nm, or more preferably from 450 nm to 700 nm, or even more preferably from 400 nm to 800 nm. A good candidate fiber for use as input/output optical fiber 228 is the SM450 fiber from Thorlabs (Newton, NJ, USA) which has an outer jacket or cladding diameter of 0.245 mm and is highly transmissive from 488 nm to 633 nm but nonetheless has adequate light transmissivity from 430 nm to 800 nm wavelengths for use with interferometer 100.
Test surface 240 is that surface that is provided by the user whose topography is to be measured by interferometer system 300 wherein the topographical data can comprise a series or an array of individual displacement measurements. The displacement can be defined as that distance along optical axis 230 from measurement spot 238 on test surface 240 to a suitable, yet somewhat arbitrary, point on optical axis 230 such as, for example, where optical axis 230 intersect the apex of secondary mirror surface 216 or, for example, where optical axis 230 intersects the aperture of input/output optical fiber 228. Since what is generally desired as an output from interferometer system 300 is the change in displacement as interferometer 200 is scanned over test surface 240, the actual displacement end-point within interferometer 200 is arbitrary, although it must not change during the scanning and measurement processes. Alternately, interferometer 200 with interferometer system 300 can compute optical path differences (OPD) between the reference arm of interferometer 200 and measurement arm of interferometer 200 in which case the OPD indicates changes in displacement (the change in OPD being substantially equal to two times the change in displacement) as the interferometer is scanned in which case no end-point within interferometer 200 is utilized.
In operation, interferometer 200 is scanned or translated across test surface 240 in a linear, curved, piecewise-linear, or areal pattern such that interferometer 200 can measure the displacement to (or elevation of) test surface 240 in more than one location so the relative displacement between the two or more locations can be determined. Test surface 240 is generally a surface of an article of manufacture such as an optical surface such as, for example, the surface of a mirror, a window, or a lens. Test surface 240 can be substantially planar, or curved such as spherical, aspherical, free-form, cylindrical, acylindrical, parabolic, or even elliptical in shape. Test surface 240 can have a width as small as 0.5 mm or a width of up to 5000 mm or more. Test surface 140 can have a sag, or a range of displacement, of from less than 2 nanometers up to 1000 millimeters. The perimeter shape of test surface 240 can be substantially circular, elliptical, square, rectangular, hexagonal, or polygonal. Test surface 240 can be reflective having a reflectivity (to a certain band of wavelengths) greater than 90%, or absorptive such that 90% or more of the light incident upon it (within a certain band of wavelengths) is absorbed, or transmissive in which more than 50% of the light incident upon it (within a certain band of wavelengths) passes through test surface 240. In this example, test surface 240 can be specular and accordingly be highly polished, or test surface 240 can have a slight texture and if textured the standard deviation of the width of the features of the texture is preferably less than half the width of measurement spot 238 on test surface 240. Finally test surface 240 can be substantially perpendicular to optical axis 230 at measurement spot 238 or test surface 240 can be tilted with respect to optical axis 230, the amount of tilt being less than 5°, or up to 10°, or even 20° or more, although greater amounts of tilt have corresponding less amounts of light throughput through the measurement arm of interferometer 200.
Interferometer 200, like most interferometers, can be described as having four arms: a source arm, a reference arm, a measurement arm, and an output arm, some of which overlap or even share the same components in interferometer 200. The source arm of interferometer 200 is that arm that sources light into interferometer 200 and includes input/output optical fiber 228 and secondary mirror surface 216. The reference arm of interferometer 200 is that arm that provides reference light to interfere with light from the measurement arm and includes secondary mirror surface 216 and reference mirror surface 206 of reference mirror 204. The measurement arm of interferometer 200 is that arm that provides measurement light to interfere with light from the reference arm and includes secondary mirror surface 216, primary mirror surface 210 of primary mirror 208, and test surface 240. The output arm of interferometer 200 is that arm that outputs light from interferometer 200 and includes input/output optical fiber 228 and secondary mirror surface 216 of secondary mirror 214.
The prescription of this second exemplary configuration of the optics of interferometer 200 is presented in
In this example, the combined surface figure errors of reference mirror surface 206 and primary mirror surface 210 should be significantly less than the wavelength of light to ensure good contrast of the resulting spectral interference fringes in spectrograph 320; the figure error of reference mirror surface 206 can be less than 0.5 microns RMS, or preferably less than 100 nanometers RMS over the clear aperture of reference mirror surface 206. Likewise, in this example the surface figure error of primary mirror surface 210 can be less than 0.5 microns RMS, or preferably less than 100 nanometers RMS over the clear aperture of primary mirror surface 210.
The reflective coating of reference mirror surface 206, primary mirror surface 210, and secondary mirror surface 216 can comprise a metal such as aluminum, chromium, silver, gold, or even silicon, and can have a thin transparent protective coating, such as silicon dioxide, installed atop the reflective coating. In this example, the reflective coating of reference mirror surface 206 can preferably have substantially the same spectral reflectance properties as the reflective coating of primary mirror surface 210, or the reflective coating of reference mirror surface 206 can be less reflective than the reflective coating of primary mirror surface 210 such that after accounting for the reflectivity of the test surface 240 the intensity of the measurement light entering the input/output optical fiber 228 is approximately the same intensity (i.e., within 20% of one another) as the reference light entering the input/output optical fiber 228.
In this second example, the CTE of the material of upper spacer 202 and/or lower spacer 203 can be less than 10 parts per billion (PPB) per degree C., or preferably less than 5 PPB, or more preferably the CTE of the upper spacer 202 and/or lower spacer 203 is less than 2 PPB. These low-CTE requirements can be illustrated by an example: if the reference arm temperature changes by 0.1 degrees C., the length of the upper spacer 202 is 100 mm, and the CTE of the material of upper spacer 202 is 10 parts per billion (PPB) per degree C., then the optical path length of the reference arm will change by 2×0.1×0.1×10×10−9 meters or 200 picometers—an amount greater than the potential measurement accuracy of the present invention.
The method by which reference mirror 204, primary mirror 208, and secondary mirror 114 are bonded or attached to upper spacer 202 and/or lower spacer 203 should also not cause temperature-induced stresses and strains which can cause nanometer-scale movements, or even sub-nanometer scale movements, of the components with respect to one another. For example, if the optical components are all fabricated from ULE, then an organic UV glue or metallic or polymeric fasteners should not be employed to fasten the components together. In this example, a more preferable way to join the glasseous opto-mechanical components (i.e., upper spacer 202, lower spacer 203, reference mirror 204, primary mirror 208, and secondary mirror 214) of interferometer 200 together is to apply a bonding agent composed of a mixture of water, sodium hydroxide, and sodium silicate to the mating surfaces of the components. With this process, known at times as hydroxide catalysis bonding (HCB), it is known that as the water evaporates, the sodium hydroxide and sodium silicate cause the glasseous optical components to chemically combine with one another such that they in effect become a unitary glass object. The resulting unitary glass object has substantially the same optical, thermal, and mechanical properties as the original glass of which the bonded components are composed.
With reference to
Source light within fiber light cone 150 that is incident upon secondary mirror surface 216 then reflects from secondary mirror surface 216 in accordance with the Law of Reflection into an outer portion of primary light bundle 252 (as seen in
As mentioned above, source light within fiber light cone 250 that is incident upon secondary mirror surface 216 then reflects from secondary mirror surface 216 in accordance with the Law of Reflection into an outer portion of primary light bundle 252 and an inner portion reference light bundle within reference light bundle 180 as seen in
A portion of the light of measurement spot 238 is reflected, in accordance with the Law of Reflection, from test surface 240 into reflected test light 270. If test surface 240 is substantially perpendicular to optical axis 230 then reflected test light 270, like test light 268, can have symmetry about optical axis 230, and occupy similar, if not substantially identical, overlapping spatial envelopes (ignoring any shadowing effects caused by arms 224) between test surface 240 and lower secondary surface 220. If test surface 240 is not perpendicular to optical axis 230 then reflected measurement light will not have symmetry about optical axis 230. In either case, small portions of reflected test light 270 will be incident on photodetectors 222 on lower secondary surface 220, and photodetectors 222 are configured as part of a sub-system used to determine the tilt of test surface 240 such that retrace errors associated with interferometer 200 can be removed as described in connection with
That portion of reflected test light 270 that is not incident on one of photodetectors 222 nor incident on arms 224 can be incident on primary mirror surface 210, and subsequently reflect from primary mirror surface 210 in accordance with the Law of Reflection into returned measurement light 266. If test surface 240 is substantially perpendicular to optical axis 230 then returned measurement light 266, like measurement light 264, can have symmetry about optical axis 230 (ignoring any shadowing effects caused by arms 224), and occupy similar, if not substantially identical, overlapping spatial envelopes between primary mirror surface 210 and secondary mirror surface 216. If test surface 240 is not perpendicular to optical axis 230 then returned measurement light 266 will not have symmetry about optical axis 230.
A portion of returned measurement light 266 can then be incident on secondary mirror surface 216 and reflect from secondary mirror surface 216 into entering fiber light 274 in accordance with the Law of Reflection. If test surface 240 is substantially perpendicular to optical axis 230 then entering fiber light 274, like exiting fiber light 272, can have symmetry about optical axis 230, and occupy similar, if not substantially identical, overlapping spatial envelopes between input/output optical fiber optic 228 and secondary mirror surface 216. If test surface 240 is not perpendicular to optical axis 230 then entering fiber light 274 will not have symmetry about optical axis 230.
For the present invention the value of the magnification, hereinafter referred to as “M”, can be between 0.1 and 10.0, but for exemplary purposes will have a value of 2.0 (meaning the measurement arm is twice as long as the source arm and the diameter of measurement spot 238 is twice the diameter of the aperture of input/output optical fiber 228). In the following calculations the length of the measurement arm will be referred to as the Measurement Arm Length, or “MAL”, and the length of the source arm will be referred to as the Source Arm Length, or “SAL”. Using the values found in
The reflective surfaces comprising interferometer 200, namely secondary mirror surface 216, reference mirror surface 206, and primary mirror surface 210, can and will have subtle manufacturing flaws that result in surface topographies that differ somewhat, and generally uncontrollably, from the ideal or as-designed surface prescription. These surface figure errors can be less than 1.0 μm peak-to-valley, or preferably less than 0.10 μm peak-to-valley. These surface figure errors can cause spurious variations in OPL (optical path length) and OPD (optical path difference which is the difference in optical path length between the measurement and reference arms of interferometer 200) which can limit the accuracy of the displacement measurements of interferometer 200 to approximately the amount of the OPD variation. Further complicating matters is that, since the three reflective surfaces will generally not have perfect rotational symmetry due to the manufacturing errors, then the amount of OPD error will be a strong function of the tilt of test surface 240 with respect to optical axis 230.
Photodetectors 222 (e.g., photodetectors 222A through 222C) are provided and configured to detect shifts in the intensity of reflected test light 270 associated with tilts of test surface 240, similar to the illustrations of
In the present invention, either interferometer 100 of Example 1 or interferometer 200 of Example 2 can be incorporated into an interferometer system 300.
As shown in
Referring more specifically to
In this example, the requirements and characteristics of the light source are: (1) that the output light pass through a small-diameter aperture such as a 5 μm diameter associated with a single-mode fiber; (2) that as much optical flux passes through the output aperture as possible; (3) that the coherence length of the light is greater than or equal to 1 mm, and (4) that the output photon flux is broad-band, although other types and/or numbers of requirements and/or characteristics of the light source may be used in other examples. For example, typically laser 304 is a single-mode fiber and has a core diameter—and exit aperture diameter—of less than 10 μm, and in some examples preferably less than or equal to 5 μm. The optical spectral flux exiting laser 304 in this example should be as great as possible, being at least 100 μW/nm, or in some examples advantageously at least 200 μW/nm, or in other examples advantageously greater than 1 mW/nm. Finally, in this example the spectrum of the light exiting the light source is broadband, and also of a wavelength range that the downstream image sensor of the camera 322 is responsive to. In particular, in this example light in the range of 450 nm to 650 nm is advantageous, while light from 400 nm to 800 nm is even more advantageous, although in other examples other ranges may be preferred such as from 700 nm to 2400 nm.
One of ordinary skill in the art will appreciate that the laws of etendue generally restrict the ability of a small light source to output relatively large spectral flux values into a small angularly envelope. However, in this example a laser driver 302 and a laser 304 comprising a supercontinuum laser can economically meet the desired flux emission values with a small (e.g., 5 μm diameter) aperture as well as the desired wavelength range. A supercontinuum laser often produces significant amounts of light above 800 nm; these wavelengths of light are generally not needed or used by examples of the claimed technology, and if not removed can propagate into interferometer 100 and be absorbed by components or surfaces inside the interferometer 100 thereby generating undesirable heat and internal thermal gradients. Since these internal thermal gradients can cause poor displacement measuring performance, it is desirable to filter these longer wavelengths or otherwise prevent them from entering the interferometer 100.
The filter assembly 306 has an input coupled to an output of laser 304 and an output coupled to source fiber optic 308, although other components and/or elements in other configurations may be used. Filter assembly 306 has provisions for filtering the unwanted wavelengths from the light output from laser 304, although other types of filters may be used. In other examples, the filter assembly 306 may also have provisions for filtering unwanted polarizations from the light output from laser 304 and for ensuring that the polarization passing through the filter assembly 306 and into the source fiber optic 308 is of a known polarization state and orientation, although the filter assembly may have other types and/or numbers of provisions.
The source fiber optic 308 is used to couple the filtered light output by the filter assembly 306 to an input of fiber optic coupler 310. The source fiber optic 308 is in some examples preferably a single-mode fiber, having a core diameter less than 10 μm, or in some examples preferably less than 5 μm, and transmits all wavelengths of light that are used by interferometer 100, such as 400 nm to 800 nm, to the interferometer with minimal attenuation. Additionally, since the light output by the filter assembly 306 can be polarized, the source fiber optic 308 can have polarization-preserving or polarization-maintaining properties. Further, since the laser driver 302 and laser 304 generate heat, in this example the laser driver 302 and laser 304 are placed a sufficient distance from interferometer 100 so the performance of interferometer 100 is not affected by the heat generated by these heat-generating sources. In this example the length of the source fiber optic 308 is at least one meter to provide the sufficient distance, or in other examples at least two meters, provided the extra length of fiber does not significantly attenuate those wavelengths used by interferometer 100 (or interferometer 200).
Fiber optic coupler 310 can be a three-port device that is used to either combine or to split optical signals being transmitted through fiber-optics. In the example embodiment shown in
The input/output optical fiber 128 is used to couple the light from filter assembly 306 through fiber optic coupler 310 to an input of interferometer 100 as well as to couple light output by interferometer 100 to fiber optic coupler 310. The input/output optical fiber 128 is in some examples preferably a single-mode fiber, having a core diameter less than 10 μm, or in some examples preferably less than 5 μm, and transmits all wavelengths of light that are used by interferometer 100, such as 400 nm to 800 nm, to (and from) the interferometer 100 with minimal attenuation. Further, since the laser driver 302 and laser 304 generate heat, in this example the laser driver 302 and laser 304 are placed a sufficient distance from interferometer 100 so the performance of interferometer 100 is not affected by these heat generating sources. In this example the length of the input/output optical fiber 128 is at least one meter to provide the sufficient distance, or in other examples at least two meters, provided the additional length does not significantly attenuate any of the wavelengths transmitted by the input/output optical fiber 128.
Continuing with reference to
The camera 322 captures an image of the optical signal or spectrum created by the spectrograph 320 and converts the image to an electronic format. In one example, the camera 322 is a line camera, wherein the image sensor of the camera 322 comprises a row of pixels arranged linearly, and onto which a spectral image is projected by spectrograph 320. In such a case, there can be between 256 and 16,384 pixels in the image sensor whose length can be up to 100 mm, and the imaging frame rate can be up to 200,000 captured images per second. More preferably, in this example the spectrograph 320 and camera 322 may be operative with two-dimensional spectral images. In this two-dimensional example, the camera 322 can have an image sensor whose pixels are arranged in a two-dimensional array wherein the pixel count can be from 640×480 pixels up to 10,000×5000 pixels, the size of the image sensor can be from 3.2 mm×2.4 mm up to 50 mm×25 mm, and the frame rate can be between 10 images/second up to 50,000 images/second. The camera 322 in this example is preferably a monochrome camera (as opposed to color) and has a gray-scale bit depth of from 8 bits up to 20 bits, although other types of cameras may be used. The output of camera 322 is coupled to an input of a digital processing system 324.
The digital processing system 324 may include one or more processors, a memory 334, and/or a communication interface, which are coupled together by a bus or other communication link, although the digital processing system 324 can include other types and/or numbers of elements in other configurations and also other types of processing systems or other computing devices may be used. The processor(s) of digital processing system 324 may execute programmed instructions stored in memory 334 for any number of the functions described and illustrated herein. The processor(s) of digital processing system 324 may include one or more CPUs or general-purpose processors with one or more processing cores, for example, although other types of processor(s) can also be used although the digital processing system 324 may comprise other types and/or numbers of components and/or other elements in other configurations.
By way of example only, the digital processing system 324 also could be a conventional microprocessor with an external memory or the digital processing system 324 can be a microcontroller with all memory located onboard. In another example, the digital processing system 324 could be a digital signal processor (DSP) integrated circuit, which is a microcomputer that has been optimized for digital signal processing applications, including centroid computations, regression, and curve-fitting. In yet another example, the digital processing system 324 can be a graphical processing unit (GPU) integrated circuit, which is a microcomputer that has been optimized for parallel-processing applications. The digital processing system 324 can be as simple as a sixteen-bit integer device for low-cost applications or the digital processing system 324 can be a thirty-two bit or sixty-four bit or higher floating-point device or system for higher performance when cost is not an issue. Also, by way of example only, the digital processing system 324 can be an FPGA (Field-programmable gate array) or a CPLD (complex programmable logic device) which are attractive for use in examples of this technology owing to their compact and cost-effective hardware implementations.
The memory 334 of the digital processing system 324 stores these programmed instructions for one or more aspects of the present technology as described and illustrated herein, such as for generating spectral content values of light output by interferometer 100 and for determining displacement or some other property of test surface 140 or a test object as described and illustrated herein for execution by the processing unit by way of example, although some or all of the programmed instructions could be stored elsewhere. A variety of different types of memory storage devices, such as random access memory (RAM), read only memory (ROM), hard disk, solid state drives, flash memory, or other computer readable medium which is read from and written to by a magnetic, optical, or other reading and writing system that is coupled to the processor(s), can be used for the memory.
Examples of one or more portions of the claimed technology as illustrated and described by way of the examples herein may also be embodied as one or more non-transitory computer readable media having instructions stored thereon for one or more aspects of the present technology, such as the memory of the digital processing system 324. The instructions in some examples include executable code that, when executed by one or more processors, such as the processor(s) of the digital processing system 324, cause the one or more processors to carry out steps necessary to implement the methods of the examples of this technology that are described and illustrated herein.
A communication interface or bus associated with digital processing system 324 operatively couples and communicates to the spectrograph 320, the camera 322, and the DAQ 328 by a communication system, although other types and/or numbers of communication systems with other types and/or numbers of connections and/or configurations to other devices and/or elements can also be used.
As mentioned earlier a plurality of photodetectors, such as photodetectors 122A through 122E coupled to the arms 120A through 120E of secondary spider support structure 120, are provided to detect a portion of the reflected test light 170 reflected from test surface 140. The output of a photodetector 122A through 122E is an electronic signal which is output to an input of data acquisition system (DAQ) 328 through photodetector output lines 330. DAQ 328 can comprise an analog to digital converter (A/D or ADC) that converts the electronic signal present on the photodetector output lines 330 to a digital format and outputs the digital data to the digital processing system 324 through DAQ output 332. In this example, the DAQ's 328 analog-to-digital converter (ADC) sub-system can have 16 bits of resolution, although 20 bits of resolution is preferred. Further, if, as shown in the example in
Interferometer system output 326 is an electronic signal line that couples an output of digital processing system 324 to an input of a downstream electronic device such as a client computer or a display (not shown). As such interferometer system output 326 can be a serial bus such as a USB or SPI bus, for inter-computer communications, or HDMI in the case where the downstream electronic device is a display. The data communicated through interferometer system output 326 bus can be the displacement measured by interferometer system 300, the topography of test surface 140, as well as other data, such as meta-data (such as, for example, the date and time of the measurement, the speed of the measurement, details about the object having test surface 32 being measured, etc.) about the displacement measurement process.
An example of a method for measuring displacement with the interferometer system 300 will now be described with reference to
Light that exits interferometer 100 (or similarly, interferometer 200) exits through input/output optical fiber 128 and is transmitted to fiber optic coupler 310 and a portion of which is routed into output fiber optic 318 whereupon it is transmitted to, and enters, spectrograph 320 as seen in
The spectrograph 320 spectrally disperses the wavelengths of the broadband reference light and projects the spectrum onto the image sensor of the camera 322. This reference light is then available to produce interference fringes on the image sensor of the camera 322 with any light from the measurement arm of interferometer 100 that is concurrently projected onto the image sensor. The spectrograph 320 also spectrally disperses the received measurement light and projects the spectrum onto the image sensor of the camera 322. This dispersed measurement light interferes with the dispersed reference light and produces interference fringes on the image sensor of the camera 322.
In this example, another requirement to produce high contrast interference fringes is that the two interfering beams are coherent with one another, which means that the optical path difference (OPD) between the lengths of the propagation paths of the two interfering beams (namely the measurement arm path and the reference arm path) is less than the coherence length of the light being interfered. Indeed, it is the OPD information that contains information about the displacement between interferometer 100 and test surface 140 at measurement spot 138. The OPD is equal to the difference of the optical path length between the reference arm and the measurement arm, i.e., OPD=OPLref−OPLmeas (or equivalently, OPD=OPLmeas−OPLref).
The optical path length of the reference arm, OPLref, is equal to twice the sum of the geometrical distance from the aperture of input/output optical fiber 128 to secondary mirror surface 116 and the distance from secondary mirror surface 116 to reference mirror surface 106 along optical axis 130, and is substantially constant. The optical path length of the measurement arm, OPLmeas, is equal to twice the sum of the geometrical distance from the aperture of input/output optical fiber 128 to secondary mirror surface 116 and the distance from secondary mirror surface 116 to primary mirror surface 110 and the distance from primary mirror surface 110 to test surface 140 along the optical axis 130, and is not substantially constant but varies in accordance with the elevation of test surface 140 at the location of measurement spot 138 as interferometer 100 is scanned over test surface 140. Indeed, it is the changing value of the quantity OPLmeas which is to be determined, which can be found from the interference equation:
where It is the total interference value, Imeas is the intensity of the light from the measurement arm, Iref is the intensity of the light from the reference arm, and λ is the wavelength of the light being interfered.
It is the spectral interference pattern described by Equation 1 that is captured by camera 322. Further, the spectral interference pattern captured by camera 322 is digitized by camera 322 and the digital representation of the spectral interference pattern is output to digital processing system 324. Software executing within digital processing system 324 then mathematically analyzes the captured and digitized spectral interference pattern and determines a value for OPD from which a value of OPLmeas can be determined. Note that for interference fringes to form the absolute value of OPD must be greater than 0.0. Further, the absolute value of the OPD must be less than the coherence length of laser 304; the coherence length can be less than or equal to 5.0 mm, or, in some cases, up to 10 mm or even 100 mm.
The ability of interferometer system 300 to measure OPLmeas, changes in OPLmeas, displacements, and the topography of test surface 140 can be very good. For example, if the spectral bandwidth is 200 nm wide (i.e., if λ of Equation 1 spans 200 nm), and spectrograph 320 has a resolution of 0.005 nanometers, then some 200/0.005=40,000 sample points will be available across the digitized spectral interference pattern, and the software executing within digital processing system 324 can then repeatably determine OPLmeas to better than 1 nm (one standard deviation), or, when the SNR (Signal to Noise Ratio) of the captured spectral interference pattern exceeds 25:1 the OPLmeas determination can be better than 0.10 nm (one standard deviation). The displacement measuring rate of interferometer system 300 can be as fast as the frame rate of camera 322, outputting over 1000 displacement measurements per second, or even up to 50,000 displacement measurements/second when camera 322 is a two-dimensional camera or even up to 200,000 displacement measurements/second when camera 322 is a linear line-camera.
In the absence of systematic errors of interferometer 100, the repeatability of a determined value of OPLmeas (especially when the test surface is tilted between measurements) can be used as a proxy for the accuracy of interferometer system 100. However, one source of systematic error is caused by primary mirror surface 110. If primary mirror surface 110 is perfect and has no surface figure errors and is perfectly aligned with respect to optical axis 130, then primary mirror surface 110 will not impart any systematic errors to the displacement measurement process. However, because primary mirror surface 110 cannot be manufactured perfectly, nor can it be installed and aligned perfectly in interferometer 100, then primary mirror surface 110 can introduce systematic errors into the displacement-measurement process. One way primary mirror surface 110 can cause systematic errors is that, given a constant displacement of test surface 140, a different tilt of test surface 140 will cause the reflected test light 170 to be incident on a different portion of primary mirror surface 110, and because of imperfections in the topography or surface figure of primary mirror surface 110 will cause spurious changes in the value of OPLmeas. That is, different values of test surface 140 tilt can cause erroneous changes in OPLmeas even when the actual displacement to test surface 140 at measurement spot 138 is kept substantially constant. This measurement error is similar to so-called retrace errors commonly found in the art in reference to areal interferometry in which light rays reflected from a test surface trace a slightly different path than expected (due to interactions between tilts in the test surface and surface figure and material homogeneity errors in the optics of the interferometer) in the interferometer along the optical path to the point where the interference fringes are created, and the corresponding errors in the optical path length within the measurement arm creates errors in the measurement of the topography of the test surface. Unlike in areal interferometry, however, in which retrace errors cannot be corrected, a method to characterize, calibrate, and substantially correct the retrace errors present in interferometer 100 is possible and is described below.
One way to correct the retrace problems of interferometer 100 is by calibrating or characterizing the spurious erroneous changes in OPLmeas with changes in the tilt of test surface 140 at measurement spot 138. The calibration can be accomplished by keeping the displacement substantially constant, intentionally tilting test surface 140 (e.g., by carefully rotating test surface 140 about measurement spot 138), and noting the value, or change in value, of OPLmeas with the amount and direction of the tilt of test surface 140. Then during the process of measuring the topography of test surface 140, any errors in OPLmeas caused by (localized or bulk) tilts of test surface 140 can be known and subtracted from the determined value of OPLmeas. This calibration and characterization process requires information about the amount and direction of the tilt of test surface 140; the information can be provided by the photodetectors 122. For example, with reference to
During the surface tilt calibration and characterization process for retrace error correction, intensity data of reflected test light 170T on each of the photodetectors 122A through 122E is output by photodetector output lines 230A through 230E to DAQ 228 which then digitizes the data output by photodetectors 122A through 122E and transmits the digitized photodetector output data to digital processing system 224 through DAQ output 232. Software executing on digital processing system 224 can then associate data from photodetectors 122A through 122E with a measured erroneous change in OPLmeas. Importantly, during the calibration process, test surface 140 is intentionally tipped or tilted through the entire operational surface-tilt envelope of interferometer 100, the envelope can be up to ±10.0° of rotation about the X and Y axes, or in this example preferably up to ±20.0° of rotation about the X and Y axes, while maintaining a constant displacement of test surface 140 at measurement spot 138. For every value of intentionally-induced tilt of test surface 140 the values of the output of each of the photodetectors 122A through 122E and OPLmeas are determined and stored in memory of digital processor 124. Then, when measuring and determining the topography of an unknown test surface, which will generally have unknown and/or unanticipated surface tilts, for a given surface displacement measurement the value of the photodetectors 122A through 122E can be determined, its associated OPLmeas error can be recalled from memory of digital processor 124, and the associated OPLmeas error can be subtracted from the value of OPLmeas determined during the measurement process thereby removing systemic retrace errors caused by, for example, imperfections in the optics of interferometer 100 (especially primary mirror surface 110). Alternately, when measuring and determining the topography of an unknown test surface, the ratio of the values of the photodetectors 122A through 122E can be determined, an associated OPLmeas error can be recalled from memory of digital processor 124, and the associated OPLmeas error can be subtracted from the value of OPLmeas determined during the measurement process.
Again, these systemic errors caused by imperfections in the interferometer's optics interacting with a tilted test surface are akin to so-called retrace errors commonly found, and generally not corrected, in areal type interferometers. The calibration process described above for removing test-surface-tilt-induced-errors from the process of measuring the topography of test surface 140 is a key benefit of the present invention.
Having thus described the basic concept of the invention, it will be rather apparent to those skilled in the art that the foregoing detailed disclosure is intended to be presented by way of example only and is not limiting. Various alterations, improvements, and modifications will occur and are intended to those skilled in the art, though not expressly stated herein. These alterations, improvements, and modifications are intended to be suggested hereby, and are within the spirit and scope of the invention. Additionally, the recited order of processing elements or sequences, or the use of numbers, letters, or other designations, such as arrows in the diagrams therefore, is not intended to limit the claimed processes to any order or direction of travel of signals or other data and/or information except as may be specified in the claims. Accordingly, the invention is limited only by the following claims and equivalents thereto.
This application claims the benefit of U.S. Provisional Patent Application Ser. No. 63/522,023, filed Jun. 20, 2023, which is hereby incorporated by reference in its entirety
| Number | Date | Country | |
|---|---|---|---|
| 63522023 | Jun 2023 | US |
