Patent Application
20210302233
This invention relates to the field of spectroscopy and more particularly to a compact Raman spectroscopy system and method for providing enhanced quantitative analysis for process control.
Raman spectroscopy is a well-known technique that can be used to observe vibrational, rotational and other low-frequency modes in molecules. Raman scattering is an inelastic process whereby monochromatic light typically provided by a laser interacts with molecular vibrations phonons or other excitations resulting in the energy of the laser photons being shifted up or down. Due to conservation of energy the emitted photon gains or loses energy equal to energy of the vibrational state.
Many Raman measurements suffer from fluorescence, which forces usage of longer wavelength (lower energy) excitation lasers to mitigate against the fluorescent signal overwhelming the Raman signal, thereby making the latter impossible to extract. Usage of longer excitation wavelengths facilitates extraction of Raman signals from fluorescent samples but at a cost of reduced sensitivity in the silicon CCD detectors that capture spectrometer signals.
Known Raman probes that capture a Raman spectra covering the entire range of wavenumbers from 0 cm−1 to 4000 cm−1 can be accomplished by use of:
(1) a single laser source with a large spectrometer incorporating long sensors to capture photons at all relevant wavenumbers with sufficient resolution;
(2) a single laser source with multiple spectrometers/detectors that each cover a different wavelength range (e.g. silicon and InGaAs);
(3) multiple laser sources with a single spectrometer, or
(4) multiple laser sources with separate spectrometers configured to capture multiple Raman spectra each covering a smaller range of wavenumbers.
Examples of the use of multiple laser techniques are disclosed by:
Each of the referred-to references focuses on capture of multiple Raman spectra using a dual-laser configuration. However, the references fail to disclose the means for selecting wavelengths used in the spectral analysis based on the material selected and the characteristics of the spectrometer utilized.
Hence, there is a need in the industry for a compact Raman probe and spectrometer system that provides for improved quantitative analysis using two or more probe laser wavelengths and a method for selecting the laser probe wavelengths to enhance a quantitative analysis of a target material under investigation for different applications.
The Raman spectral concatenation concept described herein allows use of a single, relatively compact spectrometer to collect both Fingerprint and Stretch Raman spectra (i.e., collected Raman wavelengths) and a method for selecting the laser source wavelengths to provide for enhanced quantitative analysis of target material under investigation. In accordance with the principles of the invention, the Fingerprint spectrum is captured using one excitation wavelength, whereas the Stretch spectrum is captured using a second wavelength selected based on a quantum efficiency of the spectrometer and the first wavelength. The selection of one or more of the laser source wavelengths in the manner disclosed, herein, provides for enhanced signal to noise ratio so as to enhance the performance of a quantitative analysis of a target material under investigation.
A compact dual-wavelength Raman probe configured to provide two or more separate laser wavelengths selected in a manner to provide enhanced quantitative analysis of material under investigation is disclosed Described herein are embodiments in which two laser sources may be integrated within the housing of (or internal to) a Raman probe or external to the housing of a Raman probe.
Described herein are embodiments in which light output emitted by two lasers sources may be combined in a common optical path, wherein the emitted light may be combined using either wavelength beam combining with dichroic mirrors or geometric beam combining.
Described herein are embodiments of a Raman Probe utilizing co-alignment of the excitation and collection light utilizing a same optical axis.
Described herein are embodiment of a Raman Probe utilizing a spatially offset of the excitation and collection lights utilizing separate optical paths
Described herein are embodiments of a method for selecting the wavelengths of emitted by two laser sources in a Raman Probe wherein the wavelengths of the laser sources or probes are selected in a manner based, in part, on the quantum efficiency of a spectrometer used for the analysis of the light reflected by the target material.
In accordance with the principles of the invention, the wavelengths of the probe lasers used in a dual-wavelength Raman probe are selected based on the quantum efficiency of a spectrometer comprising a single detector array (silicon, InGaAs, or any other detector array) within the spectrometer. The quantum efficiency of a detector is a measure of the ratio of collected to incident photons versus wavelength and is a common characteristic of spectrometers supplied by manufacturers.
In accordance with the principles of the invention, the probe laser wavelengths may be determined for different applications based on the quantum efficiency of the spectrometer and the material in a target object such that a desired Raman spectra is substantially coincident to a peak of the detector quantum efficiency and, hence, achieving higher signal to noise ratio.
In accordance with the principles of the invention, the selection of Raman excitation wavelengths based on the quantum efficiency of the spectrometer allows shifting of both the Fingerprint and Stretch regions of the Raman spectrum to wavelengths at which silicon detectors (or similar detectors) have relatively high quantum efficiency.
In one aspect of the invention, Raman spectra of each of the two laser sources may be captured separately and subsequently concatenated, or stitched together, to provide a single spectral scan encompassing the entire range of data, including the Fingerprint and Stretch regions, wherein the signal-to-noise ratio of the Raman signal in the Stretch region is enhanced.
In accordance with one aspect of the invention analyzing each data set independently is also possible, while collecting the spectra from both excitation wavelengths simultaneously may also be possible.
The compact dual-wavelength Raman probe, disclosed herein, may include optics to configure the output beam of each laser source to have a circular, an elliptical or an elongated cross-section, approximating a shape of a circular or a shape of the elongated emission region of the laser near-field.
In one aspect of the invention, the light generated by the laser sources may be emitted toward a target object or material under investigation and the resultant scattered signal light is transmitted by the compact Raman probe via an optical beam that may also have a corresponding elliptical cross-section. The excitation and collection paths may be co-linear (i.e., co-aligned) or separate (e.g., spatially-offset (see USPPA 20080076985) or transmission geometry (see U.S. Pat. No. 8,085,396)). An optical fiber incorporating a core having dimensions approximating those of the returned scattered light beam, transmits the returned scattered light to the entrance aperture of a spectrometer.
In accordance with the principles of the invention of the dual-wavelength Raman probe disclosed herein, the dual-wavelength Raman probe may include external cavity lasers (ECLs) that may be integrated into the probe as wavelength-stabilized laser sources. See, for example, U.S. Pat. No. 9,059,555, “Wavelength-Stabilized Diode Laser,” the contents of which are incorporated by reference herein. Or may retain the ECLs external to the Raman probe.
In accordance with the principles of the compact Raman probe disclosed herein, a distributed Bragg reflector (DBR) or distributed feedback (DFB) lasers may comprise a wavelength-stabilized laser source that may be integrally incorporated into the Raman probe or may be retained external to the Raman probe.
In accordance with the principles of the compact dual-wavelength Raman probe disclosed herein, the light emitted by a laser may be used as the pump source for a non-linear optical (NLO) conversion to produce a different wavelength, e.g., by second-harmonic generation (SHG), third-harmonic generation (THG), or any other non-linear optical process.
In accordance with the principles of the invention of a compact dual wavelength Raman probe, the selection of a second wavelength is based, in part, on a first wavelength and a spectral efficiency of the spectrometer used to collect the Raman signal.
For a better understanding of exemplary embodiments and to show how the same may be carried into effect, reference is made to the accompanying drawings. It is stressed that the particulars shown are by way of example only and for purposes of illustrative discussion of the preferred embodiments of the present disclosure and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention. The description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice. In the accompanying drawings:
In this exemplary embodiment, a dual wavelength Raman probe 100 includes a housing 105 and two external light sources 110 and 120, (hereinafter referred to as lasers or laser sources. However, it would be recognized that the light sources 110 and 120 may similarly be non-lasing sources, e.g., a super luminescent diode) coupled via optical fibers 113 and 123, respectively, to the internal optics within housing 100. The lasers 110 and 120 may emit light in a single spatial mode or in multiple spatial modes. Optical couples 111, 112, 121, and 122 are known devices for coupling optical fibers to equipment or devices.
The laser sources 110 and 120 may be any laser device or system; preferably laser sources 110 and 120 are wavelength-stabilized laser sources having narrow bandwidth. One class of lasers that may be used as a wavelength-stabilized laser source is an external cavity laser. See, for example, U.S. Pat. Nos. 9,059,555 and 9,577,409, which are assigned to the assignee of the instant application and whose contents are incorporated, in their entirety, by reference, herein, and describe exemplary external wavelength stabilized diode lasers.
Sources 110, 120 may also be semiconductor lasers that incorporate gratings within their structure, such as a distributed feedback (DFB) or distributed Bragg reflector (DBR) laser.
Laser sources 110, 120 may also be a DFB or DBR laser coupled to a non-linear optical element for second- or third-harmonic generation of shorter wavelength laser light, as is well-known in the art.
The compact dual-wavelength Raman probe 100 further includes optics 115, 125 to configure the output beam of the laser sources 110, 120. Exemplary components shown in
Collimated light beams 131 and 132 are combined into a single collimated beam 138 by use of a first dichroic mirror 135 and reflecting mirror 136, wherein mirror 136 redirects light beam 132 towards first dichroic mirror 135. First dichroic mirror 135 further passes light beam 132 and redirects light beam 131 to form collimated beam 138.
In one aspect of the invention, a single short pass filter (not shown). with cut-off wavelength designed to pass the wavelengths emitted by the first laser 110 and the second laser 120 but blocks wavelengths beyond the longer of the two wavelengths (i.e., light beams 131, 132) may be placed after the light beams 131, 132 are combined into collimated beam of light 138.
The probe (excitation, illumination) light beam 138 is transmitted through a second short-pass dichroic mirror 140, with transmission characteristics schematically depicted in inset 141, to lens 150 which focuses the combined light, comprising the wavelengths emitted by the first laser 110 and the second laser 120, onto the target object 160 along light path 145
Light scattered from the target object 160 will include Raman, Rayleigh and fluorescent components, which may be collected by lens 150 and directed back towards the second dichroic mirror 140 through light path 145. In this illustrated case, dichroic mirror 140 is configured to reflect the longer Stokes-shifted Raman photons into collimated beam 155. Light at wavelengths longer than the filter cutoff, including at the two excitation wavelengths, will, to a great extent, pass through second dichroic mirror 140 and be largely eliminated from beam 155.
In one aspect of the invention, additional optical elements (not shown) may be included in the light path of light beam 138 to shape light beam 138. For example, light beam 138 may be shaped into a circular beam such that the light beam 138 (i.e., combined first excitation wavelength and second excitation wavelength) forms an annular region on said target object 160. In one aspect of the addition, the optical elements may be configured to adjust a diameter of the annular region projected onto the target object. In accordance with another aspect of the invention, the additional optical elements (not shown) may be included the light path of light beam 138 to shape light beam 138 into an elliptical or elongated shape.
The spatial extent of the excitation light on the target 160 may be sufficiently long to give rise to off-axis scattered light, which may result in the reflection of a range of wavelengths—including those that would be preferentially excluded—by the second dichroic mirror 140 into beam 155. The design of dichroic mirror 140 preferably is such that unwanted light is eliminated as much as is possible.
Dichroic mirror 140 may be an edge filter that is designed to direct wavelengths of the Raman scattered light toward spectrometer 190, along a single optical fiber or axis (i.e., co-aligned), while substantially removing other light near the pump wavelengths.
In an embodiment of the invention disclosed in which the Stokes signal wavelength is to be detected, the dichroic mirror 140 is a short-pass filter that reflects wavelengths longer than that of the pump wavelength and substantially removes wavelengths at and shorter than the pump wavelengths from optical beam 155, as shown.
In an embodiment of the invention disclosed, in which anti-Stokes signals are to be detected, the dichroic mirror 140 is a long-pass filter that reflects wavelengths shorter than that of the pump wavelength and substantially removes wavelengths at and longer than the pump wavelengths from optical beam 155.
Dichroic mirror 140 is typically used at a 45° angle of incidence and, in the embodiment shown in
For detection of Stokes signals, long-pass dichroic filter 170 is designed to transmit wavelengths longer than its cutoff wavelength, as shown in inset 171. Lens 180 focuses the filtered light onto the entrance facet of optical fiber 185, which transmits the light to slit 191 of a compact spectrometer 190.
The filter 170 may be one of: a dichroic filter, a volume holographic grating filter, and a fiber Bragg grating filter, used in combination with focusing and collection optics or any filter that provides the required wavelength-dependent blocking and transmitting capabilities. Exemplary filters include STOPLINE® single notch filters and RAZOREDGE® ultra-steep long-pass edge filters for Stokes detection and ultra-steep short-pass edge filter for anti-Stokes detection. STOPLINE and RAZOREDGE are registered Trademarks of IDEX Health & Science LLC, Rohnert Park, Calif.
Spectrometer 190 is designed to diffract light input through slit 191 to a linear silicon detector array (not shown). The range of light diffracted onto the array is limited by the design of the spectrometer's diffraction grating and linear extent of the detector array as is well-known in the art. Accordingly, a spectrometer's grating and detector may be configured so that the detector receives a limited range of wavelengths, e.g., approximately 791 nm to 934 nm for Stokes signals. An exemplary 2048-element linear detector may have a resolution of approximately 1 cm−1 (i.e., 1 wavenumber, wherein wavenumber is a term of art within the optical field) in both the Fingerprint and Stretch regions of the spectrum if detected separately.
In another embodiment of the invention, the light from lasers 110 and 120 of
In this third exemplary embodiment of a dual-laser Raman probe, the remaining elements (components) and operation shown in
Collection lens 151 collects the Raman light generated in response to the illumination of the target object 160 with the combined excitation (or illumination light) light 138 and directs the collected Raman light, i.e., light beam 155, to filter 170, which operates to remove the excitation wavelengths from the collected Raman light, as previously discussed.
In this fourth exemplary embodiment of a dual-laser Raman probe, the remaining elements (components) and operation shown in
By increasing a distance 710 between the excitation light wavelengths 702 and collected light wavelengths 704 regions below a surface of target object 160 may be observed.
For example, optical device 810 may comprise an optical probe that may be used to scan target object 160 while emitting excitation wavelengths 702 and collecting Raman wavelengths 704. The tip of optical probe may include an optically clear material (e.g., plurality of optical fibers) that receive excitation wavelengths from lens 150 and a second, separate, optically clear material (e.g., optical fibers) that collect Raman light wavelengths and provide the collected Raman wavelengths to collection lens 151. Alternatively, optical device 810 may be a stationary device that includes a platform on to which target object may be placed or contained. In one aspect of the invention, optical device 810 may include a plurality of optical fibers, for example, that receive excitation wavelengths 702 and a second plurality of optical fibers, for example, that collect Raman light wavelengths 704 and provide the collected Raman light wavelengths to collection lens 151. In addition, the first set of optical fibers and the second set of optical fibers may be orientated as shown in
Although optical device 810 is shown external to housing 110, it would be recognized that optical device 810 may be internal to housing 110.
Spatial distance 710 between the excitation wavelengths 702 and the Raman wavelength 704 may be varied, for example, by utilizing different ones of collection fibers 920.
As with the arrangement shown in
In this illustrated embodiment, spatial distance 710 may be measured horizontally, vertically or diagonally with respect to the transmissive fibers and the receptive fibers.
In aspect of the invention, a mask may be utilized to limit the number of receptive devices receiving the Raman light wavelengths. The mask may be used for determining a minimum separation (or maximum separation distance). Returning to
In one aspect of the invention, physical separation 710 of excitation wavelength 702 from collected wavelength 704 may be achieved through the use of a central illumination (excitation) region and an annular collection region. In another aspect of the invention, physical separation 710 of excitation wavelength 702 from collected wavelength 704 may be achieved through the use an annular illumination (excitation) region and a central collection region. In another aspect, the collection wavelength region may be physically moved or masked from the excitation wavelength region to allow for variable distance between the excitation wavelength illumination area and the collection light wavelength area.
In another aspect of the invention. the excitation wavelength region and the collection wavelength region may be oriented on opposite sides of the target object, 160, in a so-called transmission configuration.
In still another embodiment of the invention, the excitation wavelengths 702 may be directed toward target object 160 at an angle. Similarly, the collected wavelengths 704 may be collected at an angle with respect to the target object 160.
Although exemplary embodiments of a dual wavelength co-aligned/reflective Raman Probe, with external lasers (
In addition, it would be known by those skilled in the art that the combining of the excitation wavelengths discussed may be performed by any of a known number of known wavelength combining methods (e.g., wavelength beam combining with dichroic mirrors or geometric beam combining, see U.S. Pat. No. 7,420,996).
In accordance with the principles of the invention, the excitation lasers 110, 120 disclosed, herein, may be operated simultaneously, concurrently or sequentially. Sequential operation eliminates spurious signals e.g., fluorescence, that may be generated when both laser sources were to be operated simultaneously. However, it would be understood that simultaneous or concurrent operation has been considered and both concurrent and sequential operation of the laser sources is considered within the scope of the invention. Hence, when the operation of the sources is concurrent, the laser light of the two sources may be combined as in joining together to form a single light beam composed of two wavelengths (e.g., wavelength beam, geometric beam combining (see U.S. Pat. No. 7,420,996, for example).
In the case of where the operation of the sources is sequential, then the laser light of one source is considered “combined” with the non-presence of light from the second laser light source such that a single beam of a single wavelength is formed.
Exemplary Raman pump wavelengths currently in use are 532 nm, 638 nm, 785 nm, 830 nm, and 1064 nm. As is known in the art, shorter wavelength pump wavelengths yield higher Raman scattered signals as the Raman intensity is proportional to λ−4. However shorter pump wavelengths are more likely to give rise to fluorescence, which can overwhelm the Raman spectral features. The method of Raman concatenation offers the possibility of mitigating the negative impact of fluorescence with the shorter wavelength excitation source since fluorescence is wavelength dependent while the Raman signal is both proportional to the λ−4 and shifts with respect to the excitation wavelength. This allows for the possibility of quantifying a Raman signal in the Stretch band when it is not possible to quantify a Raman signal in the Fingerprint region when high levels of fluorescence are present. Finally, the specific wavelength of the short or long wavelength laser source can be selected to mitigate any fluorescence resonance effects.
Further, Stokes spectra are typically more intense than are anti-Stokes spectra. As is well known in the art, a Stokes shift of v (measured in wavenumbers, i.e., cm−1) will give rise to a Raman signal wavelength, λs, related to the probe wavelength, λp, by:
1/λs=1/λp+v (1)
Generally, the “Fingerprint” region of the spectrum includes wavenumbers less than about 2000 cm−1 whereas the “Stretch” region includes wavenumbers ranging from about 2000 cm−1 to 4000 cm−1.
In accordance with the principles of the invention, the two probe wavelengths designated as λp1 210 and λp2 220 excite the Stretch and Fingerprint regions of the Raman spectrum, respectively. In this illustrated case, the second excitation wavelength λp1 is of a shorter wavelength than the first excitation wavelength λp2220.
Further illustrated is an exemplary wavelength range associated with a Fingerprint region, Δv2, 223 expressed in wavenumbers. The illustrated Fingerprint region 213 is shown as extending from Raman signal wavelengths λs21 225 to λs22 227, which are associated with the first excitation wavelength λp2 220. Wavelengths λs21 215 and λs22 217 are determined from wavelength λp2 220 by shifted values V21 and V22, respectively, wherein shifted values V21 and V22 may be determined from equation 1, above.
In this illustrated example, Raman signal wavelength λs21 225 is conventionally shifted 1-2 nm (nanometers) from first excitation wavelength λp2 220 to avoid saturating the spectrometer with the backscattered pump light, while Raman signal wavelength λs22 227 is determined by calculating the wavelength associated with the Fingerprint wavenumber range, Δv2 223:
1/λs22=1/λs21+Δv2. (2)
Further illustrated is a wavelength range associated with the Raman signal Stretch region, Δv1, 213 expressed in wavenumbers. The illustrated Stretch region is shown as extending from Raman signal wavelengths λs11 215 and λs12217, which are associated with the second excitation wavelength λp1 210. Wavelengths λs11 215 and λs12 217 are determined from wavelength from λp1 210 by shifted values V11 and V12, respectively, wherein values V11 and V12 may be determined from equation 1, above.
Accordingly, Raman signal wavelength λs11 215 is selected to essentially coincide with λs21 225 so as to enable the detector element of a spectrometer to be utilized for both pump lasers, while Raman signal wavelength λs12 217 is determined by calculating the wavelength associated with the Stretch wavenumber range, Δv1 213, wherein the difference between λs11 and λs12 define the Stretch region.
1/λs12=1/λs11+Δv1. (3)
Further shown is an exemplary quantum efficiency curve, QE(λ) 230 of the spectrometer to be used for the collection and analysis of the Raman signals generated by the first and second excitation wavelengths.
Accordingly, with a proper selection of the second excitation wavelength λp1 210 and the first excitation wavelength λp2 220 the generated Raman signals within both the Stretch region and the Fingerprint region may be captured by the detector element of a single spectrometer.
For the purposes of describing the subject matter regarded as the invention to those skilled in the art, the Fingerprint region wavenumber range and Stretch region wavenumber range are approximately equal, i.e., Δv1≈Δv2, resulting in λs11≈λs21 and λs21≈λs22.
Furthermore, while second excitation wavelength λp1 210 and first excitation wavelength λp2 220 may be selected to provide for the capture of both the Fingerprint and Stretch region using a same detector array, the selection of wavelengths λp1 210 and λp2 220 in accordance with the principles of the invention provides for the enhancement of the analytical performance of the spectrometer.
In accordance with the principles of the invention, at step 310, a first excitation wavelength (i.e., λp2) is selected. The first excitation wavelength is associated with the Fingerprint region of the Raman signals reflected or scattered by the target object when illuminated by the first excitation wavelength.
The first excitation wavelength, λp2, is selected to be as short as possible to mitigate fluorescence of the Raman spectra generated by the inelastic scattering of the first excitation wavelength by the target object. Thus, first excitation wavelength, λp2, is determined based on the Raman target sample 160 under investigation and its particular fluorescence characteristics when illuminated by the excitation wavelength.
For example, it would be known in the art that a first excitation wavelength, λp2, for target classes of materials such as heavy petroleum (oil), biological materials, pharmaceutical materials and clear liquids may be selected as 1064 nm, 830 nm, 785 nm, and 532 nm, respectively.
For purpose of teaching the invention claimed, a wavelength such as 785 nm (nanometers) may be selected as the first excitation wavelength, wherein 785 nm is selected to minimize the fluorescence generated by the target object when illuminated by the first excitation wavelength.
The desired range of the Fingerprint region wavenumbers (Δv2) is selected based on a desired spectral range and resolution of the spectrometer (e.g., 2000 cm′) at step 320.
The selection of the first excitation wavelength, λp2′ and Δv2 defines the longest measured wavelength of the spectrometer (λs22) (step 330) as
λs22=1/[Δv2+1/λp2] (4)
In this exemplary example with the use of a first excitation wavelength, λp2, of 785 nm, the longest measured wavelength λs22 may be determined from equation 4 above, as 931 nm.
Inspection of the quantum efficiency spectrum associated with the spectrometer to be used in the collection and analysis of the Raman signals may then be performed to determine a peak wavelength of the spectrometer quantum efficiency response, QE(λ), in the determined Fingerprint region (i.e., between wavelength λp2 (which is approximately equal to λs21) and λs22 (step 340).
The quantum efficiency curve, QE(λ), provides a measure of the efficiency of the spectrometer to collect the Raman signals over a known wavelength band. For example, and for purposes of describing the invention claimed, the quantum efficiency response curve (λQE) within the range of the determined Fingerprint region may be determined from current measurements or previous measurements of the response characteristics of the spectrometer.
For example, and for the purpose of describing the invention claimed to those skilled in the art, and with reference to
The Raman shifted peak of interest (vpoi) may then be determined for the specific chemical compound under investigation (i.e., target object) at step 350. For example, and for the purposes of describing the invention claimed to those skilled in the art, a Raman shifted peak of interest for a specific target object may be determined to be associated with a wavenumber of 3000 cm−1.
The second excitation wavelength (λp1) for quantitative analysis in the Stretch region may then be determined at step 360 as:
λp1=1/[vpoi+1/λQE] (5)
Accordingly, the second excitation wavelength, (λp1) may be determined based on the Raman shift peak of interest, which is associated with the specific target object and the peak quantum efficiency of the spectrometer within the Fingerprint region, which is defined by the selection of the first excitation wavelength.
From the exemplary wavelength selected as the first excitation wavelength (λp2) 220, for the exemplary Raman shifted peak of interest (vpoi) of 3000 cm−1 and the peak quantum efficiency (λQE) 235, a second excitation wavelength (λp1) 210 may be determined as 645 nm.
As would be appreciated, the selection of the second excitation wavelength in the manner disclosed in equation 5 provides for a coincidence of the Raman peak of interest wavelengths with the peak wavelength (λQE) of the spectrometer quantum efficiency within the Fingerprint region.
Hence, the analysis of the Raman signals associated with the second excitation wavelengths is performed at, or substantially close to, the peak quantum efficiency of the spectrometer which results in better analytical performance of the target object.
Although the selection of the second excitation wavelength is determined based of the peak quantum efficiency, as expressed in equation 5, and the most significant spectra performance may be achieved when the determined second excitation wavelength is coincident with the peak quantum efficiency, it would be recognized that a non-peak quantum efficiency value may similarly be utilized to determine the second excitation wavelength. That is, in accordance with the principles of the invention, the term “peak” as used with regard to the term “peak quantum efficiency” need not be the “peak” or maximum value as used in the ordinary and customary sense. Rather the term “peak” as used herein is considered to be a range about the maximum (or peak) value of spectra quantum efficiency. For example, the range may be defined by a range of +/−10 percent of the wavelength number of the maximum value of the spectra quantum efficiency. Similarly, the range may be defined as +/−15 percent of the wavelength number of the maximum value of the spectra quantum efficiency. In another example, the range may be defined as the wavelength numbers within 3 dB of the maximum value of the spectra quantum efficiency. See for example,
Accordingly, the determination of a second excitation wavelength based on equation 5 may be more generally expressed as:
λp1=1/[vpoi+1/(λQE+(+/−δ))] (6)
Thus, in accordance with the principles of the invention, the term “peak” is considered to be one of: the maximum value of the response spectra of the spectrometer and a range about the maximum value of the response spectra of the spectrometer.
In accordance with the principles of the invention, a first spectral Raman component generated by the excitation of the target object by a first excitation wavelength, is captured, filtered, received, processed and stored as shown in steps 310, 365, 368, 371, 374, respectively. More specifically, a target object is illuminated by a first excitation wavelength (i.e., λp2), which has been selected to minimize the fluorescence generated by the target object when illuminated by the first excitation wavelength. The Raman scattered light reflected or scattered by the target object is captured at step 365. The Raman scattered light is then filtered at step 368 and provided to the spectrometer at step 371. At step 374, a spectral analysis performed on the reflected or scattered signals provided to the spectrometer are then stored at step 374.
At step 360, a second excitation wavelength (i.e., λp1) is determined based on the first excitation wavelength and the quantum efficiency of the spectrometer within the Fingerprint region determined based on the first excitation wavelength, as discussed above.
In accordance with the principles of the invention, after a determination of the second excitation wavelength based on equation 5 above, is made, an evaluation of the determined second excitation wavelength may be made with regard to wavelength performance of conventional laser devices in order to determine a suitability of using conventional lasers having known wavelength output.
That is, the wavelengths of one or more selected conventional lasers may be evaluated with regard to equation 6 to determine which of the one or more selected conventional lasers may be used in place of specially designed lasers that output a wavelength based on equation 5.
A second Raman component generated by the excitation of the target object 160 by the determined second excitation wavelength, is captured, filtered, received, processed, and stored as shown in steps 377, 381, 384, 387, 390, respectively. Specifically, the target object 160 is illuminated by the second excitation wavelength at step 377. The scattered or reflected Raman wavelengths associated with the second excitation wavelength are captured (step 381) and filtered at step 384. At step 387, the Raman wavelengths are provided to the spectrometer and at step 390, the results of a spectral analysis performed by the spectrometer are stored.
At step 395, the first and second Raman spectral component data are concatenated, or combined together, wherein the first Raman spectral component may be used to determine an identification of a compound of the target object 160, while the second Raman spectral component may be used to determine a concentration of the compound of the target object. Alternatively, the first and second Raman spectral may be processed independently to provide a more detailed analysis of the target object.
The selection of the first and second excitation wavelengths in accordance with the principles of the invention provides for enhanced quantitative analysis as the Raman spectrum coincides (or substantially coincides) with a peak of the quantum efficiency of the spectrometer within the Fingerprint region. The increased signal-to-noise ratio of the received Raman signals caused by the coincidence of the Raman signal with the peak of quantum efficiency of the spectrometer provides for an increase in the distinguishing features of the target object (or the component under analysis within the target object).
Accordingly, the dual-laser Raman Probe described herein provides opportunities to monitor, for example, a pharmaceutical bioreactor (i.e., a sealed vessel in which bacteria are grown in an aqueous liquid). In another aspect, an H Stretch band may be used as a calibration standard against which CH and NH Stretch bands to be monitored. For example, the CH and NH Stretch bands may be used to determine changes in proteins within a pharmaceutical bioreactor as proteins are generated by a bacteria and food (carbohydrates) are consumed. In accordance with another application of the dual-laser Raman probe disclosed herein, a concentration of an additive may be determined by calibration using the Raman signal of pure water.
Referring to
In accordance with the principles of the invention, selection of the second excitation wavelength (e.g., 680 nm), based on the first wavelength and the spectral efficiency of the spectrometer, provides for a quantum efficiency of 90 percent at 200 cm−1 whereas a wavelength shift associated with a 3600 cm−1 wavenumber provides a quantum efficiency of 82%. Hence, the selection of the second excitation wavelength in accordance with the principles of the invention provides significant improvement of the analysis of the Raman signals.
Hence, selection of the dual excitation wavelengths through the matching of the peak of the quantum efficiency curve to a particular wavenumber band of interest, in accordance with the principles of the invention, provides for an enhancement in the signal processing capability of the spectrometer.
An example, of the selection of the first and second excitation wavelengths may be determined as follows:
Accordingly, a selection of a second excitation wavelength of 827.0676692 nm in accordance with the principles of the invention provides an improved, enhanced, signal-to-noise ratio in the Raman signal analyzed.
Furthermore, with the enhanced Stretch band signal, the entire enhanced Stretch band may be used for additional data as input for chemometrics algorithms or as orthogonal data to validate of data from the Fingerprint region.
For example, the Raman probe excitation wavelength selection method described, herein, may have use in medical diagnostics as fats and proteins may be monitored using the CH and NH bands and water using the OH band.
Analysis of the CH and NH bands, with the improved or enhanced signal analytical performance described, herein, may help diagnose inflammation or other pathological conditions.
The Raman probe excitation wavelength selection method described, herein, may have use in pharmaceutical process analytics for compound grown in water (H2O) as analysis of such compounds using near-infrared (NIR) spectroscopy is not effective.
The Raman probe excitation wavelength selection method described, herein, may have use to analyze petrochemicals as CH bands are important and where water is generally a contaminant.
Generally speaking, the invention encompasses the use of a device as described herein in medical diagnostics and in analyses associated with petrochemical processing or bioreactors.
Specifically,
In accordance with the principles of the invention, dual-wavelength Raman probe technology disclosed, herein, enables new applications in the process automation market. For example, the use of -H Stretch region vs. Fingerprint region may provide for improved quantitative measurement of changes in concentration or predictive quantitation of concentration. For example, the dual-wavelength Raman probe with the wavelength selection as presented, herein, may be directly applicable to enhance the analysis of:
In summation, a dual-wavelength Raman probe system comprising first and second excitation wavelengths impinge upon a target object and the reflected or scatted wavelength by the target object are collected and analyzed by a spectrometer. In accordance with the principles of the invention, the excitation wavelengths are selected based on the target object and the quantum efficiency (or within a known range) of the spectrometer in order to improve the signal to noise ratio of the Raman signals by having the Raman signals substantially coincide with the peak quantum efficiency of the spectrometer. Collection of the Raman signals substantially coincident with the peak quantum efficiency of the spectrometer provides for an improved signal to noise ratio of the Raman signal.
Although the invention has been described with regard to “a wavelength” emitted by the laser source or operated on by the Raman and Rayleigh scattering it would be recognized that the term “a wavelength” is a term of art and refers to a wavelength or a band of wavelengths around a nominal desired wavelength. The invention has been described with reference to specific embodiments. One of ordinary skill in the art however appreciates that various modifications and changes can be made without departing from the scope of the invention as set forth in the claims. Accordingly, the specification is to be regarded in an illustrative manner, rather than with a restrictive view, and all such modifications are intended to be included within the scope of the invention. Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. The benefits, advantages, and solutions to problems, and any element(s) that may cause any benefits, advantages, or solutions to occur or become more pronounced, are not to be construed as a critical, required, or an essential feature or element of any or all of the claims.
As used herein, the terms “comprises”, “comprising”, “includes”, “including”, “has”, “having”, or any other variation thereof, are intended to cover non-exclusive inclusions. For example, a process, method, article or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. In addition, unless expressly stated to the contrary, the term “or’ refers to an inclusive “or” and not to an exclusive “or”. For example, a condition A or B is satisfied by any one of the following: A is true (or present) and B is false (or not present); A is false (or not present) and B is true (or present); and both A and B are true (or present).
The terms “a” or “an” as used herein are to describe elements and components of the invention. This is done for convenience to the reader and to provide a general sense of the invention. The use of these terms in the description herein should be read and understood to include one or at least one. In addition, the singular also includes the plural unless indicated to the contrary. For example, reference to a composition containing “a compound” includes one or more compounds. As used in this specification and the appended claims, the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise.
All numeric values are herein assumed to be modified by the term “about,” whether or not explicitly indicated. The term “about” generally refers to a range of numbers that one of skill in the art would consider equivalent to the recited value (i.e., having the same function or result). In any instances, the terms “about” may include numbers that are rounded (or lowered) to the nearest significant figure.
It is expressly intended that all combinations of those elements that perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Substitutions of elements from one described embodiment to another are also fully intended and contemplated.
This application claims, as a Continuation in Part application, pursuant to 35 USC 120, priority to and the benefit of the earlier filing date of patent application Ser. No. 16/831,611, filed on Mar. 26, 2020, the contents of which are incorporated by reference, herein. This invention disclosed, herein, is related to that subject matter recited and taught in U.S. Pat. No. 10,359,313, the contents of which are incorporated by reference, herein.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 16831611 | Mar 2020 | US |
| Child | 17198173 | US |
