CN116818740A - Terahertz sensitive detection imaging system and method - Google Patents
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- G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
- G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
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Abstract
The invention provides a terahertz sensitive detection imaging system and a terahertz sensitive detection imaging method. The system comprises a first optical comb light source, a second optical comb light source, a terahertz light source, a beam combiner, a dichroic mirror, a first focusing lens, an optical filter, a second focusing lens and a photoelectric detector; the first optical comb light source and the second optical comb light source have small difference in repetition frequency, the output light of the two optical comb light sources sequentially passes through a dichroic mirror and a first focusing lens to be focused on the surface of a sample to be detected after being collinear by the beam combiner to generate Raman scattered light signals, and when the time delay of the two optical combs is longer than the service life of a high-energy vibration dynamic molecular energy level excited by the pumping optical comb, the repetition frequency of the second optical comb is reduced, so that continuous detection of the Raman signals is realized; the terahertz light source outputs terahertz waves to act on the surface of a sample to be detected, so that the molecular configuration of the sample is changed, and the position of a Raman peak is changed. The system and the method realize terahertz spectrum sensitivity, rapidness and high duty ratio measurement by a double-comb Raman imaging, optical comb frequency modulation and surface Raman enhancement technology.
Description
Technical Field
The invention relates to the technical field of material detection, in particular to a terahertz sensitive detection imaging system and a terahertz sensitive detection imaging method.
Background
The terahertz imaging technology has wide application fields and huge application value, so that the terahertz imaging technology is a hot spot for research in recent years. At present, the conventional terahertz imaging system cannot realize high-sensitivity imaging detection due to the lack of a sensitive detection device in a terahertz wave band. The advent of coherent anti-stokes raman scattering has prompted the development of biomedical and materials science in recent years for various applications such as cancer detection, metabolic analysis, drug discovery, and the like. Double optical comb coherent anti-stokes raman scattering spectroscopy (DC-CARS) is particularly appreciated because of its unique ability to rapidly acquire high resolution raman spectra in the fingerprint region. However, since DC-CARS 99% of the laser energy is not used for CARS (coherent anti-stokes raman scattering) processes, the duty cycle of its effective CARS signal is less than 1%, which greatly limits the spectral acquisition rate and signal-to-noise ratio. The terahertz spectrum sensitive detection is converted into coherent anti-Stokes Raman scattering spectrum detection through specific vibration energy level excitation, and the duty ratio is improved by combining with optical comb frequency modulation, so that a new method is provided for developing a new terahertz wave band sensitive imaging technology.
Disclosure of Invention
An object of the present invention is to solve one or more of the problems occurring in the prior art, in view of the disadvantages of the prior art. For example, one of the purposes of the present invention is to provide a terahertz sensitive detection imaging system and method, which excite a sample molecule to be detected through terahertz waves to cause the configuration change of the sample molecule to generate the shift of a raman peak, and utilize a double-optical comb raman imaging technology and an optical comb frequency modulation technology to realize the rapid and high duty ratio measurement of a coherent raman spectrum and capture the change of the raman peak of the molecule; in addition, by combining a Raman signal enhancement technology, the intensity of scattered signals is enhanced, the detection sensitivity is improved, and the sensitive detection and imaging of a sample are realized.
The invention provides a terahertz sensitive detection imaging system, which can comprise a first optical comb light source, a second optical comb light source, a terahertz light source, a beam combiner, a dichroic mirror, a first focusing lens, a second focusing lens, an optical filter and a photoelectric detector, wherein the repetition frequencies of the first optical comb light source and the second optical comb light source are slightly different, the output light of the first optical comb light source and the output light of the second optical comb light source are collinearly at the beam combiner, then are focused on the surface of a sample to be detected through the dichroic mirror and the first focusing lens in sequence to generate a Raman scattered light signal, the Raman scattered light signal returns along an original light path through the first focusing lens and then is reflected to the optical filter through the dichroic mirror, and the optical filter filters the Raman scattered light signal and is focused on the photoelectric detector through the second focusing lens; the light output by the first optical comb light source is used as pump light, the light output by the second optical comb light source is used as detection light, and when the time delay of the two optical combs is longer than the molecular energy level life of the high-energy vibration state excited by the pump optical comb, the repetition frequency of the second optical comb is reduced, so that the continuous detection of Raman signals is realized; the terahertz light source outputs terahertz wave waves to act on the surface of a sample to be detected, the molecular configuration of the sample to be detected is changed, so that Raman peaks generated on the surface of the sample to be detected are offset, raman scattered light signals with the offset are reflected to the filter plate in the bicolor mirror after sequentially passing through the first focusing lens along an original light path, the filter plate filters out the Raman scattered light, and the Raman scattered light is focused through the second focusing lens and then transmitted to the photoelectric detector to be collected and measured so as to realize terahertz spectrum detection.
Further, the repetition frequency of the first optical comb light source and the repetition frequency of the second optical comb light source may have a slight difference, that is, a repetition frequency difference therein.
Further, the time delay of the pump light and the probe light pulse may be, where the number of pulse pairs is indicated.
Further, the device can further comprise a signal generator, wherein the signal generator is used for modulating the repetition frequency of the second optical comb light source, and the signal generator modulates the repetition frequency of the second optical comb light source into the repetition frequency after the molecular energy level life time of the high-energy vibration state is longer than the molecular energy level life time of the high-energy vibration state.
Further, the sample to be tested can also comprise rough metal, and the sample to be tested is adsorbed on the surface of the rough metal.
Further, the optical fiber optical comb can also comprise a first reflecting mirror and a second reflecting mirror, wherein the output light of the second optical comb light source is reflected by the first reflecting mirror and then is input to the beam combiner; the terahertz wave irradiates the surface of the sample to be detected after being reflected by the second reflecting mirror; the terahertz wave acts on the surface of the sample to be detected at the same point as the point where the light output by the first optical comb light source and the light output by the second optical comb light source are focused on the surface of the sample to be detected through the first focusing lens, the molecular configuration of the sample to be detected is changed by the terahertz wave, the change quantity of the position of the Raman peak is the change quantity, the change quantity is the terahertz wave frequency, and c is the light speed.
Further, the beam combining sheet forms an included angle of 45 degrees with the light propagation direction output by the first optical comb light source and the light propagation direction output by the second optical comb light source respectively; the dichroic mirror forms an included angle of 45 degrees with the propagation direction of the raman scattered light signal.
Further, the photodetector may be an avalanche photodiode detector.
Another aspect of the present invention provides a terahertz sensitive detection imaging method, which is applied to the terahertz sensitive detection imaging system described above, and may include the following steps: focusing a beam of pumping light and a beam of detection light on the surface of a sample to be detected after being collinear, and generating a Raman scattering signal when the time delay between the two optical combs is smaller than the molecular energy level life of a high-energy vibration state excited by the pumping optical comb; after the time delay between the two optical combs is longer than the molecular energy level service life of the high-energy vibration state, the repetition frequency of the optical comb is modulated by the signal generator, and the repetition frequency of the second optical comb light source is modulated immediately; the terahertz wave acts on the surface of the sample to be detected, and the molecular configuration of the sample to be detected is changed, so that the Raman peak generated on the surface of the sample to be detected is deviated; and filtering the shifted Raman scattering optical signal caused by terahertz excitation, and focusing on a photodetector for Raman imaging.
Compared with the prior art, the invention has the beneficial effects that at least one of the following is included:
(1) The system and the method can cause the change of the sample molecular configuration and generate the shift of the Raman peak through the excitation of the terahertz wave to the sample molecule to be detected, and capture the change of the molecular Raman peak by combining the double-light comb Raman imaging technology, so that the terahertz wave band measurement is converted into Raman signal detection, and the detection range is widened;
(2) The system and the method of the invention combine the optical comb frequency modulation technology to realize the measurement of the Raman signal with high duty ratio and realize the measurement of the coherent Raman spectrum with high speed and high duty ratio;
(3) The system and the method can improve the intensity of the Raman scattered light signal, thereby improving the detection sensitivity.
Drawings
The foregoing and other objects and features of the invention will become more apparent from the following description taken in conjunction with the accompanying drawings in which:
FIG. 1 is a schematic diagram of an exemplary embodiment of a terahertz sensitive detection imaging system of the present invention;
FIG. 2 is a schematic diagram of double optical comb Raman imaging;
fig. 3 is a schematic diagram of conventional double optical comb raman imaging.
Fig. 4 is a schematic diagram of dual optical comb raman imaging based on frequency modulation.
Reference numerals illustrate:
the device comprises a 1-first optical comb light source, a 2-second optical comb light source, a 3-terahertz light source, a 4-signal generator, a 5-first reflecting mirror, a 6-beam combiner, a 7-dichroic mirror, an 8-first focusing lens, a 9-sample to be detected, a 10-second reflecting mirror, an 11-optical filter, a 12-second focusing lens and a 13-photoelectric detector.
Description of the embodiments
Hereinafter, a terahertz sensitive probe imaging system and method according to the present invention will be described in detail with reference to the drawings and exemplary embodiments.
One aspect of the invention provides a terahertz sensitive detection imaging system. In some embodiments of terahertz sensitive detection imaging systems, as shown in fig. 1, the system may include a first optical comb light source 1, a second optical comb light source 2, a terahertz light source 3, a beam combiner 6, a dichroic mirror 7, a first focusing lens 8, a filter 11, a second focusing lens 12, and a photodetector 13.
Wherein, the repetition frequencies of the first optical comb light source 1 and the second optical comb light source 2 are slightly and adjustably different. The repetition frequency difference between the first optical comb light source 1 and the second optical comb light source 2 is the modulation offset frequency, which should be smaller than 1kHz. The repetition frequency of the first optical comb light source 1 is fixed, and the repetition frequency may be the center frequency of the second optical comb light source frequency 2 modulation. The repetition frequency of the second optical comb light source 2 may be modulated by a signal generator. After the light output by the first optical comb light source 1 and the light output by the second optical comb light source 2 are collinear at the beam combiner 6, the light sequentially passes through the bicolor mirror 7 and the first focusing lens 8 which are arranged behind the beam combiner 6, and acts on the surface of the sample 9 to be detected after being focused by the first focusing lens 8 to generate Raman scattered light signals. Due to the existence of the double optical combs of the first optical comb light source and the second optical comb light source, raman scattered light signals are generated by utilizing double optical comb Raman imaging, and the effective Raman scattered light signal duty ratio can be improved by combining with the modulation of repeated frequencies, so that the measurement of the coherent Raman spectrum with high duty ratio is realized.
The terahertz light source 3 outputs terahertz waves to act on the surface of the sample 9 to be detected. The point of the terahertz wave acting on the sample to be detected is the same point as the point of the first optical comb light source and the second optical comb light source acting on the sample to be detected. By setting terahertz wave to cause the molecular configuration change of a sample to be detected and generate the shift of a Raman peak, combining the double-optical comb Raman imaging technology, filtering the Raman scattering optical signal which is caused by the shift and is excited by the terahertz wave, focusing on a photoelectric detector for Raman imaging, and thus, the rapid measurement of a coherent Raman spectrum can be realized and the change of the Raman peak of the molecule is captured. The offset raman scattered light signals sequentially pass through the first focusing lens 8 along the original light path and then are reflected to the filter 11 by the bicolor mirror 7, the filter 11 filters out the raman scattered light and then focuses the raman scattered light by the second focusing lens 12, and the raman scattered light is transmitted to the photoelectric detector 13 for collection and measurement.
In some embodiments, the repetition frequency of the first optical comb light source may be, i.e.; the repetition frequency of the second optical comb light source may be a repetition frequency difference between the first optical comb light source and the second optical comb light source, and the repetition frequency difference may be less than 1kHz, for example, the repetition frequency difference may be 15 Hz, 50 Hz, 200 Hz, 500 Hz, or 600 Hz.
In some embodiments, the first optical comb light source 1 and the second optical comb light source 2 may be infrared optical comb light sources.
In some embodiments, the light output by the first optical comb light source may be used as pump light, as shown by a in fig. 2 for a pump optical comb with a repetition frequency. The light output by the second optical comb light source can be used as the detection light, and the detection optical comb with the repetition frequency is shown as c in fig. 2. The time delay of the pump light and the probe light pulses may be, wherein the number of pulse pairs is indicated. The pump comb excites raman vibrational transitions (transition frequency is) of the sample molecules by a two-photon process, the refractive index modulation of which is shown in fig. 2 b. The change of the refractive index of the sample to be detected is induced by the vibration of the molecules, the molecular vibration time domain diagram is shown as d in fig. 2, the change frequency is immediately induced by the detection light pulse, the light frequency shift is generated by the Doppler effect, the change of the refractive index of the sample leads to the intensity modulation of the Raman scattering light signal, the modulation frequency is shown as e in fig. 2, the modulation is shown as an interference signal which changes periodically in the time domain, the interference signal (f in fig. 2) is detected by a photoelectric detector, and the signal is subjected to Fourier transformation, so that the corresponding molecular energy level spectrum information can be obtained. As shown in fig. 3, when the time delay between the two optical combs is greater than the molecular energy level lifetime of the high-energy vibrational state excited by the pump optical comb (typically less than 10 ps), the molecules will relax freely to a low energy state, i.e., without raman scattering signals. The effective raman scattering signal time is typically on the order of microseconds. The period in which the raman scattering signal occurs is typically of the order of milliseconds. Therefore, the signal duty cycle of the traditional double optical comb Raman measurement is less than 1%, while the signal duty cycle of the double optical comb Raman measurement of the invention is close to 100%.
In some embodiments, as shown in fig. 1, the system may further comprise a signal generator 4, the signal generator 4 being configured to modulate the repetition frequency of the second optical comb light source 2. As shown in fig. 4, the repetition frequency of the second optical comb light source 2 is modulated by the signal generator immediately after the time delay between the two optical combs is longer than the molecular energy level life of the high-energy vibration state, so that the signal duty ratio can be effectively improved and the measurement speed can be improved.
In some embodiments, the system may further comprise a roughened metal on which the sample to be tested is adsorbed. The sample to be detected is adsorbed on the rough metal surface, so that the signal intensity can be improved by at least four orders of magnitude. The raman scattered light signal can be enhanced by surface enhanced raman scattering techniques. The roughened metal may be nanoporous gold or other roughened metals commonly used in the art.
In some embodiments, as shown in fig. 1, the system may further comprise a first mirror 5 and a second mirror 10. The light output by the second optical comb light source 2 is reflected by the first reflecting mirror 5 and then input to the beam combiner 6. The terahertz wave output by the terahertz light source 3 is reflected by the second reflecting mirror 10 and then irradiates the surface of the sample 9 to be measured. The point where the terahertz wave acts on the surface of the sample to be detected is the same point as the point where the light output by the first optical comb light source and the light output by the second optical comb light source are focused on the surface of the sample to be detected through the first focusing lens. The terahertz wave is a terahertz wave with the frequency of 0.1-10 THz. The terahertz wave can change the molecular configuration of a sample to be detected, so that the Raman peak position is changed, the change amount can be terahertz wave frequency, and c is the light speed.
In some embodiments, the combiner may be a combiner plate. The filter may be a short pass filter.
In some embodiments, as shown in fig. 1, the included angle between the beam combining sheet 6 and the light propagation direction of the output light of the first optical comb light source 1 may be 43 to 47 degrees. Preferably, the included angle between the beam combining sheet 6 and the propagation direction of the output light of the first optical comb light source 1 may be 45 degrees. The propagation direction of the light output by the beam combining sheet 6 and the second optical comb light source 2 after being reflected by the reflecting mirror 5 can form an included angle of 43-47 degrees. Preferably, the beam combining sheet 6 and the propagation direction of the light output by the second optical comb light source 2 after being reflected by the reflecting mirror 5 may form an included angle of 45 degrees. The included angle between the dichroic mirror 7 and the propagation direction of the raman scattered light signal returned along the optical path can be 43-47 degrees, and the light spot quality of the reflected light can be effectively guaranteed at the moment. Preferably, the dichroic mirror 7 may be angled at 45 degrees to the direction of propagation of the raman scattered optical signal back along the optical path.
In some embodiments, the photodetector may be an avalanche photodiode detector or other detector for detection in the art.
Another aspect of the invention provides a terahertz sensitive detection imaging method. In some embodiments, the terahertz sensitive detection imaging method may be applied to the terahertz sensitive detection imaging system described above, and may include the steps of:
s01, a beam of pumping light and a beam of detection light are focused on the surface of a sample to be detected after being collinear, and when the time delay between the two optical combs is smaller than the molecular energy level service life of a high-energy vibration state excited by the pumping optical comb, a Raman scattering signal is generated; after the time delay between the two optical combs is longer than the molecular energy level service life of the high-energy vibration state, the repetition frequency of the optical comb is modulated by the signal generator, and the repetition frequency of the second optical comb light source is modulated immediately;
s02, enabling terahertz waves to act on the surface of a sample to be detected, changing the molecular configuration of the sample to be detected, and enabling a Raman peak generated on the surface of the sample to be detected to deviate;
s03, filtering the offset Raman scattering optical signals caused by terahertz wave excitation, and focusing the Raman scattering optical signals on a photoelectric detector for Raman imaging.
The first point of the surface can be any point on the surface of the sample to be measured.
For a better understanding of the present invention, the content of the present invention is further elucidated below in connection with the specific examples, but the content of the present invention is not limited to the examples below.
As shown in fig. 1, the infrared optical comb light source includes a first optical comb light source 1 and a second optical comb light source 2, the center wavelength of the two optical combs is 800nm, the pulse width is 10fs (corresponding to the full width of the fourier transform limit spectrum, i.e. the measurable raman spectrum width is 188nm or 2942 cm-1), the repetition frequency of the first optical comb light source is=100 MHz, and the repetition frequency of the second optical comb light source is Δf=10 Hz, which is driven and controlled by the signal generator 4.
The first optical comb light source 1, the beam combiner 6 (the beam combiner 6 is a beam combining sheet), the bicolor mirror 7, the first focusing lens 8 and the sample 9 to be measured are arranged on the same straight line, and the second optical comb light source 2 is reflected by the first reflecting mirror 5 and is collinear with the output light of the first optical comb light source 1 after the beam combiner 6. The beam combiner 6 is placed at an angle of 45 degrees to the two optical combs. The two optical combs are focused on one point of the sample 9 to be detected through the first focusing lens 8, terahertz waves output by the terahertz light source 3 are directly irradiated on the same point of the sample 9 to be detected through the second reflecting mirror 10, the molecular configuration of the sample can be changed, and the positions of Raman peaks detected by the two optical combs are changed. The dichroic mirror 7 is disposed at an angle of 45 degrees to the raman scattered light that is shifted back along the original optical comb optical path, so that the raman scattered light is reflected on the dichroic mirror 7, and a short-pass filter 11 (which is a short-pass filter), a second focusing lens 12, and a photodetector 13 (which is an avalanche photodiode detector) are disposed on the path of the raman scattered light reflection. The filter 11 filters out the raman scattered light at an angle slightly less than 90 degrees to the optical path. The photodetector 13 is placed at a focal point where the scattered light is focused by the second focusing lens 12.
The implementation process comprises the following steps: first, the signal generator 4 drives and controls the repetition frequency of the second optical comb light source 2 to (=100 MHz, =10 Hz), and outputs the first optical comb light source 1 and the second optical comb light source 2. The second optical comb light source 2 is reflected by the first reflecting mirror 5 and is collinear with the first optical comb light source 1 after the beam combining sheet 6. The two optical combs penetrate through the dichroic mirror 7, and are focused on the surface of a sample 9 to be detected by the first focusing lens 8, so that a Raman scattering signal is generated. The sample 9 is adsorbed on the surface of the porous nano gold, the signal intensity is improved by at least four orders of magnitude through a surface enhancement technology, and the detection sensitivity is improved.
Secondly, the terahertz light source 3 directly irradiates the same point on the surface of the sample 9 to be detected through the second reflecting mirror 10, the molecular configuration of the sample is changed, and the position of the Raman peak detected by the double optical comb is changed.
And finally, the Raman scattering signal with changed Raman peak position returns along the original optical comb optical path, is reflected on the bicolor mirror 7, is filtered out by the optical filter 11, is focused on the photodetector 13 by the second focusing lens 12, and is subjected to Raman imaging.
Although the present invention has been described above by way of the combination of the exemplary embodiments, it should be apparent to those skilled in the art that various modifications and changes can be made to the exemplary embodiments of the present invention without departing from the spirit and scope defined in the appended claims.
Claims (9)
1. A terahertz sensitive detection imaging system is characterized by comprising a first optical comb light source, a second optical comb light source, a terahertz light source, a beam combiner, a dichroic mirror, a first focusing lens, an optical filter, a second focusing lens and a photoelectric detector, wherein,
the repetition frequencies of the first optical comb light source and the second optical comb light source are slightly different and adjustable, and after the output light of the first optical comb light source and the output light of the second optical comb light source are collinear in the beam combiner, the output light is focused on the surface of a sample to be detected through a dichroic mirror and a first focusing lens in sequence and a Raman scattering light signal is generated; the light output by the first optical comb light source is used as pump light, the light output by the second optical comb light source is used as detection light, and when the time delay of the two optical combs is longer than the molecular energy level life of the high-energy vibration state excited by the pump optical comb, the repetition frequency of the second optical comb is reduced, so that the continuous detection of Raman signals is realized;
the terahertz light source outputs terahertz wave waves to act on the surface of a sample to be detected, the molecular configuration of the sample to be detected is changed, so that Raman peaks generated on the surface of the sample to be detected are offset, raman scattered light signals with the offset are reflected to the filter plate in the bicolor mirror after sequentially passing through the first focusing lens along an original light path, the filter plate filters out the Raman scattered light, and the Raman scattered light is focused through the second focusing lens and then transmitted to the photoelectric detector to be collected and measured so as to realize terahertz spectrum detection.
2. The terahertz sensitive detection imaging system of claim 1, wherein the repetition frequency of the first optical comb light source and the repetition frequency of the second optical comb light source have a slight difference, i.e., wherein the repetition frequency difference is.
3. The terahertz sensitive detection imaging system of claim 2, wherein the time delay of the pump light and the detection light pulse is, wherein the number of pulse pairs is represented.
4. The terahertz sensitive detection imaging system of claim 3, further comprising a signal generator for modulating the repetition frequency of the second optical comb light source, the signal generator modulating the repetition frequency of the second optical comb light source to be greater than the molecular energy level lifetime of the high-energy vibration regime.
5. The terahertz sensitive detection imaging system of claim 1, 2, 3 or 4, further comprising a roughened metal on which the sample to be measured is adsorbed.
6. The terahertz sensitive detection imaging system of claim 1, 2, 3 or 4, further comprising a first mirror and a second mirror, wherein the light output from the second optical comb light source is reflected by the first mirror and then input to the beam combiner; the terahertz wave irradiates the surface of the sample to be detected after being reflected by the second reflecting mirror; the point of the terahertz wave acting on the surface of the sample to be detected is the same as the point of the light output by the first optical comb light source and the light output by the second optical comb light source focused on the surface of the sample to be detected through the first focusing lens, the molecular configuration of the sample to be detected is changed by the terahertz wave, the variation of the position of the Raman peak is the variation, the variation is the terahertz wave frequency, and the light velocity is c.
7. The terahertz sensitive detection imaging system according to claim 1, 2, 3 or 4, wherein the beam combining sheet forms an included angle of 43-47 degrees with the light propagation direction output by the first optical comb light source and the light propagation direction output by the second optical comb light source respectively; the dichroic mirror forms an included angle of 43-47 degrees with the propagation direction of the Raman scattered light signal.
8. The terahertz sensitive detection imaging system of claim 1, 2, 3 or 4, wherein the photodetector is an avalanche photodiode detector.
9. A terahertz sensitive detection imaging method, characterized by being applied to the terahertz sensitive detection imaging system according to any one of claims 1 to 8, comprising the steps of:
focusing a beam of pumping light and a beam of detection light on the surface of a sample to be detected after being collinear, and generating a Raman scattering signal when the time delay between the two optical combs is smaller than the molecular energy level life of a high-energy vibration state excited by the pumping optical comb; after the time delay between the two optical combs is longer than the molecular energy level service life of the high-energy vibration state, the repetition frequency of the optical comb is modulated by the signal generator, and the repetition frequency of the second optical comb light source is modulated immediately;
the terahertz wave acts on the surface of the sample to be detected, and the molecular configuration of the sample to be detected is changed, so that the Raman peak generated on the surface of the sample to be detected is deviated;
and filtering the shifted Raman scattering optical signal caused by terahertz wave excitation, and focusing on a photoelectric detector for Raman imaging.
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