A channel spectral type polarization raman spectrometer and a measuring method

Abstract

The present application relates to the field of optical technology, and more particularly to a channel spectral polarization Raman spectrometer and a measuring method. The channel spectral polarization Raman spectrometer and the measuring method are as follows: incident laser is changed into polarized incident laser; the polarized incident laser is focused on a sample plane to generate Raman effect and generate Raman scattering light; the Raman scattering light is modulated to a frequency domain by polarization, and channelized Raman spectrum is formed. The channel spectral polarization Raman spectrometer proposed in the present application adopts a polarization modulation module including an achromatic quarter-wave plate, a high-order retarder and a polarizer to modulate polarization information onto a spectrum, then records through a spectrometer, and finally demodulates the polarization information from the modulated spectrum, so that the channel spectral polarization Raman spectrometer has the advantages of higher time resolution and no moving parts.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical technology, in particular to a channel spectral type polarization Raman spectrometer and a measuring method. BACKGROUND

[0002] Raman effect was proposed by C.V.Raman and K.S.Krishnan as early as 1928, who opened the research on the interaction of light and matter inelastic scattering, and pointed out that there is a secondary scattering light with wavelength red shift in the scattered light. This secondary scattering light is called Raman scattering light, named after its discoverer. In the process of Raman scattering, the incident electromagnetic wave will cause the displacement of the electron cloud inside the molecule, so that the molecule produces induced dipole moment.

[0003] A part of the radiation light in the induced dipole moment has the same frequency as the incident light, which is called Rayleigh scattering light, which is the scattering light of the elastic interaction of light and matter. According to the modern quantum analysis point of view, when the photon interacts with the molecule in the ground state, the molecule will be excited to a short-lived virtual energy level, and then the molecule in the virtual energy level will quickly return to the ground state and release a photon with the same energy as the incident photon, which is the process of elastic scattering.

[0004] In addition to elastic scattering, there is a very small probability, usually less than one in a million, that the incident photon will have inelastic interaction with the molecule, at which time the molecule in the virtual energy level will return to a certain vibrational state instead of the ground state, and release a scattered photon with lower energy than the incident photon, that is, wavelength red shift occurs, and the scattered light at this time is called Raman scattering light, also called Stokes scattering light.

[0005] The scattering light with higher energy than the incident light is called anti-Stokes scattering light. In anti-Stokes scattering, the photon will excite the molecule originally in the vibrational state to a higher virtual energy level, and then the molecule in the virtual energy level returns to the ground state and releases a scattered photon with higher energy than the incident photon, that is, wavelength blue shift occurs. According to the Boltzmann distribution, at room temperature, the number of molecules in the vibrational ground state is more than that in the excited state, so Stokes scattering (Raman scattering) is more likely to occur than anti-Stokes scattering. Whether it is Raman scattering or anti-Stokes scattering, the frequency difference from the incident light is a constant value, which is determined by the inherent chemical structure of the molecule, so the Raman spectrum can provide the fingerprint information of the molecule, and can be used to identify and distinguish the molecules in the complex.

[0006] Raman spectroscopy corresponds to the vibration energy level of a specific molecule, and has the advantage of high specificity. Raman spectroscopy is a non-destructive detection technology, almost no sample preparation is required, no sample labeling is required, and it can measure solid, liquid and gas samples. It is an extremely superior optical detection technology. Although Raman spectroscopy has so many advantages, but because the efficiency of Raman scattering is very low (less than one millionth of the incident photons can cause inelastic scattering), therefore, to successfully observe the Raman signal and obtain effective molecular information depends largely on the ability of the instrument to collect weak Raman signals. Although the Raman effect was discovered more than 90 years ago, the rapid development and application of Raman spectroscopy technology only appeared in recent decades, which is mainly due to the development of modern laser technology, optical filtering technology and high-sensitivity detectors. The development of laser technology makes the laser smaller and more powerful, and can excite stronger Raman scattering; the development of optical filtering technology makes it possible to manufacture more efficient filters to better filter out Rayleigh scattering light and extract weak Raman scattering signals; the development of high-sensitivity detectors improves the collection efficiency of weak light signals, so that weak Raman scattering signals can be recorded.

[0007] Raman spectroscopy is widely used in biomedical and clinical diagnosis fields due to its high specificity, non-destructive, no sample preparation and labeling, etc. It is usually combined with a microscope. A typical Raman microscope system is based on a confocal microscope. The confocal property describes the ability of the microscope to reject light from outside its focal point. It is usually achieved by setting a small aperture conjugate to the point of focus of the microscope. This conjugate aperture also prevents light from out-of-focus points from entering the detector, effectively filtering out background information outside the target sample point. However, confocal also has the disadvantage of not being able to achieve real-time imaging. Image acquisition needs to be achieved through point scanning. The working principle of a typical Raman microscope system is shown in Figure 1

[0008] As shown in Figure 1 ​As shown, the incident laser is first coupled into the system by a polarization maintaining fiber, the coupling fiber is located at the focal point of the collimating mirror near one end of the system, then the collimated light becomes a larger radius parallel laser beam after collimation by the collimating mirror, then the laser is reflected by two plane mirrors and a notch beam splitter, enters the high numerical aperture microscope objective, and is finally focused on the sample plane. The high numerical aperture microscope objective can make the focused spot smaller and the laser intensity higher, making it easier to accurately excite stronger Raman signals at the target point. Moreover, the high numerical aperture microscope objective can also collect scattered light within a larger angle, thereby increasing the efficiency of signal collection. A super-narrow band-pass filter, also known as a laser line filter, is placed before the notch beam splitter. The filter is used to filter out stray light other than the laser, which is mainly from the Raman scattering of silica in the fiber, thereby ensuring the purity of the laser reaching the sample plane. Since the confocal microscope-based Raman spectrometer can only detect a single point at a time, in order to realize point scanning on the sample plane, the sample is placed on an electrically controlled displacement stage, which can realize horizontal plane movement and scanning.

[0009] The scattered light generated after the laser and the sample interact on the sample plane is collected by the same high numerical aperture objective. The collected light in this mode is called backscattered light. The backscattered light is reflected by the mirror and hits the notch beam splitter plane. The notch beam splitter is a combination of a notch filter and a beam splitter, which has a wavelength selection function. Light within a range centered on the wavelength of the incident laser will be reflected, while the rest of the light will be transmitted. Therefore, the Rayleigh scattering light in the scattered light will be reflected, while the Raman scattering light will pass through the notch beam splitter into the signal collection light path. It is worth mentioning that the successful manufacture of the notch beam splitter benefits from the development of advanced filtering technology. It not only reflects and guides the laser to the sample plane, but also enables the weak Raman signal to be extracted from the strong Rayleigh scattering background, making the Raman spectroscopy system more compact and miniaturized, greatly reducing the application cost of the instrument. The scattered light that passes through the notch beam splitter passes through another beam splitter. The beam splitter reflects light with shorter wavelengths (anti-Stokes signals and visible light background), while transmitting light with longer wavelengths, i.e. Raman scattering light. The reflected light is imaged on a face array detector by an imaging lens, realizing bright-field imaging of the sample plane. The transmitted Raman scattering light is further filtered by a notch filter to remove the Rayleigh scattering background, then focused by a lens on a fiber port, and then transmitted by the fiber to a spectrometer, realizing the recording of the Raman spectrum signal. The fiber port here is in a conjugate relationship with the laser focus spot on the sample plane, satisfying the confocal condition. SUMMARY

[0010] The present application aims to solve the above problems and provides a channel spectral polarization Raman spectrometer and a measurement method.

[0011] The technical scheme of the present application is characterized in that:

[0012] The present application provides a channel spectral type polarized Raman spectrum measurement method.

[0013] A channel spectral type polarized Raman spectrum measurement method, the method is as follows: the incident laser is changed into polarized incident laser; the polarized incident laser is focused on a sample plane to generate Raman effect to generate Raman scattering light; the Raman scattering light is polarized and modulated to the frequency domain to form channelized Raman spectrum.

[0014] Further comprising extracting polarized Raman spectrum from the channelized Raman spectrum.

[0015] The specific process of forming the channelized Raman spectrum is that the Raman scattering light sequentially passes through an achromatic quarter-wave plate, a high-order retarder and a second linear polarizer to form the channelized Raman spectrum; wherein the fast axis direction of the achromatic quarter-wave plate is 0°; the fast axis direction of the high-order retarder is 45°, and the transmission axis direction of the second linear polarizer is 0°.

[0016] The retardation of the high-order retarder is two-thirds of the cutoff frequency of the Raman spectrum signal.

[0017] The specific process of extracting the polarized Raman spectrum from the channelized Raman spectrum is as follows:

[0018] The channelized Raman spectrum is transformed from the time domain to the frequency domain;

[0019] The channelized Raman spectrum forms a low-frequency channel and two symmetrical high-frequency channels in the frequency domain,

[0020] The low-frequency channel is taken out and transformed back from the frequency domain to the time domain to extract spectral information;

[0021] The high-frequency channel is taken out and transformed back from the frequency domain to the time domain, and then phase correction is performed to extract polarization information;

[0022] The specific process is as follows:

[0023] Compared with the traditional Raman spectrometer, the channel spectral type polarized Raman spectrometer (CPRM) of the present application modulates the polarization information to different channels in the frequency domain through a polarization modulation module, and then the polarization information is recorded by the spectrometer. Finally, the polarization information is demodulated from the frequency domain by the Fourier transform method, so that the CPRM has additional polarization detection capability. The principle of channel modulation of the CPRM system is introduced below.

[0024] Analog modulation spectrum I modulated which can be expressed as

[0025]

[0026] In the formula, σ is the wave number, cm-1 ; S1, S2 and S3 are linear polarization components, dimensionless; is the phase shift, rad; introduced by the thick retarder; B is the birefringence of the retarder, dimensionless; d is the thickness of the retarder, cm;

[0027] Equation (5-1) can be further written as

[0028]

[0029] where i is the imaginary part of a complex number;

[0030] According to the frequency shift property of Fourier transform, if a signal is multiplied by an exponential term in time domain, a shift will occur in frequency domain. Therefore, the Fourier transform of the channel modulated spectrum I modulated is written as

[0031] FT{I modulated} = C0+ C -1 + C1 (5-3)

[0032] where FT{} represents the Fourier transform operation; C0is the low frequency channel containing the S0signal, and C1and C -1 are the symmetrically distributed high frequency channels, which preserve the information of S1and S2. These three channels are separated from each other in frequency domain, and can be taken out separately to do inverse Fourier transform, so as to extract S0, S1and S2respectively:

[0033] IFT{C0} = S0(σ) / 2 (5-4a)

[0034]

[0035]

[0036] where IFT{} represents the inverse Fourier transform operation; Even if the retarders are made of the same material, there are still differences in their birefringence, so the calibration of the retardation of the retarder, i.e. the calibration of the phase term in equation (5-4), is crucial, and is directly related to the accurate demodulation of S1and S2components. In the calibration process of the phase introduced by the retarder, a horizontally polarized polarizer is placed in the middle of the notch filter and the achromatic quarter-wave plate, so as to polarize the calibration light source to a known polarization state, and at this time there is a transformation relationship of equation (5-5):

[0037] IFT{C 0,calibration} = S 0,calibration (σ) / 2 (5-5a)

[0038]

[0039]

[0040] wherein: C 0,calibration , C 1,calibration , C 2,calibration is the channel in the calibration process; S 0,calibration , S 1,calibration is the polarization component of the calibration light source;

[0041] For the horizontally polarized calibration light, the S0 component and the S1 component are equal, and the S2 component is zero, at this time the exponential term of the calibration can be calculated from the following formula:

[0042]

[0043]

[0044] Substituting formula (5-6) into formula (5-4), each polarization component can be calculated by the following formula:

[0045] S0(σ)=2*IFT{C0} (5-7a)

[0046] S1(σ)=2Re{IFT{C1}*IFT{C 0,calibration} / IFT{C 1,calibtration}} (5-7b)

[0047] S2(σ)=-2Im{IFT{C1}*IFT{C 0,calibration} / IFT{C 1,calibtration}} (5-7c)

[0048] wherein: Re is the real part operation; Im is the imaginary part operation;

[0049] Only once the phase calibration is performed before the experiment starts, then the inserted polarizer can be removed, and the actual detection can be carried out. It should be noted that if the direction of each element of the polarization modulation module, the working waveband of the spectrometer, the grating ruling number and the entrance slit width of the spectrometer are changed, the calibration needs to be performed again.

[0050] A channel spectral type polarization Raman spectrum measurement method, the method is as follows:

[0051] The incident laser is adjusted to a parallel light beam after collimation by a collimating mirror, and stray light other than the wavelength of the incident laser is filtered out by an ultra-narrow band-pass filter, and then passes through a first linear polarizer and a half-wave plate, and the incident laser is changed into polarized incident laser;

[0052] The polarized incident laser is transmitted to the trap wave beam splitter after the beam splitter, and then reflected to the plane mirror, and the plane mirror is reflected to the microscope objective, and the polarized incident laser is focused on the sample plane through the microscope objective, and the Rayleigh scattering light and the Raman scattering light are generated after the polarized incident laser acts on the sample plane; the Rayleigh scattering light and the Raman scattering light are collected through the microscope objective, and then reflected to the trap wave beam splitter through the plane mirror;

[0053] The Raman scattering light is transmitted to the trap wave beam splitter, and then filtered through the trap wave filter to remove residual laser, and then modulated into a channelized Raman spectrum through the polarization modulation module, and then converged to the optical fiber entrance through the imaging lens, and finally introduced into the spectrometer through the optical fiber;

[0054] The Rayleigh scattering light is reflected to the beam splitter by the trap wave beam splitter, and then reflected to the area array detector to realize bright field imaging of the sample plane.

[0055] The incident laser is a 785nm wavelength incident laser generated by a diode laser with a central wavelength of 785nm.

[0056] (II) The application provides a channel spectrum type polarized Raman spectrometer.

[0057] A channel spectrum type polarized Raman spectrometer for realizing the channel spectrum type polarized Raman spectrum measurement method comprises a polarization laser generation system, a Raman light generation system, a Raman light collection system and a bright field imaging system connected in sequence; wherein,

[0058] The polarization laser generation system comprises a first linear polarizer and a half-wave plate arranged in sequence along an excitation light path of the incident laser.

[0059] The Raman light generation system comprises a beam splitter, a trap wave beam splitter, a plane mirror and a microscope objective arranged in sequence along a polarized incident excitation light path; and further comprises a sample, which is located at the focal point of the microscope objective.

[0060] The Raman light collection system comprises a microscope objective, a plane mirror, a trap wave beam splitter, a trap wave filter, a polarization modulation module and a collection module arranged in sequence; the polarization modulation module comprises a achromatic quarter-wave plate, a high-order retarder and a second linear polarizer arranged in sequence; wherein, the fast axis direction of the achromatic quarter-wave plate is 0°, the fast axis direction of the high-order retarder is 45°, and the transmission axis direction of the second linear polarizer is 0°; the collection module comprises an imaging lens and an optical fiber connected to a spectrometer arranged in sequence.

[0061] The bright field imaging system comprises a microscope objective, a plane mirror, a trap wave beam splitter, a beam splitter, a second imaging lens and an area array detector arranged in sequence.

[0062] The beam splitter is shared by the Raman light generating system and the bright field imaging system, the microscope objective, the plane mirror and the notch beam splitter are shared by the Raman light generating system, the Raman light collecting system and the bright field imaging system.

[0063] The polarized laser generating system comprises a collimating mirror, an ultra-narrow band-pass filter, a first linear polarizer and a half-wave plate arranged in sequence along an excitation light path of the incident laser.

[0064] The technical effect of the present application is that:

[0065] 1. The channel spectral polarization Raman spectrometer adopts a polarization modulation module comprising an achromatic quarter-wave plate, a high-order retarder and a second linear polarizer to modulate the polarization information onto the spectrum, then records through the spectrometer, and finally demodulates the polarization information from the modulated spectrum;

[0066] 2. The channel spectral polarization Raman spectrometer only needs one measurement to restore all linear polarization Raman spectral information, while the traditional polarization Raman spectrometer needs to rotate the polarizer at least three times to obtain the same amount of information, which is equivalent to making the signal acquisition time of the traditional polarization Raman spectrometer three times that of the present application, and may also introduce additional motion errors. BRIEF DESCRIPTION OF DRAWINGS

[0067] Figure 1 It is a typical Raman microscopic system working principle diagram.

[0068] Figure 2 It is a system connection schematic diagram of the channel spectral polarization Raman spectrometer.

[0069] Figure 3 It is a polarization component, an analog modulated spectrum and an FFT transform result diagram of the polypropylene fiber.

[0070] Figure 4 It is a measured polarization component and an analog restoration result diagram of the polypropylene fiber.

[0071] Figure 5 It is a CPRM restoration result diagram of the polypropylene fiber.

[0072] Figure 6 It is a CPRM restoration result diagram of the melted polypropylene.

[0073] Figure 7 It is a polarization Raman imaging result diagram of the tooth.

[0074] Reference numerals: 1, collimating mirror; 2, ultra-narrow band-pass filter; 3, first linear polarizer; 4, half-wave plate; 5, beam splitter; 6, wave-trap two-way beam splitter; 7, plane mirror; 8, microscope objective; 9, sample plane; 10, wave-trap filter; 11, achromatic quarter-wave plate; 12, second linear polarizer; 13, imaging mirror; 14, area-array detector; 15, high-order retarder. DETAILED DESCRIPTION

[0075] Embodiment 1 - A method for measuring channel-spectroscopic polarized Raman spectrum.

[0076] A method for measuring channel-spectroscopic polarized Raman spectrum, the method is as follows: the incident laser is changed into polarized incident laser; the polarized incident laser is focused on the sample plane 9 to generate Raman effect to generate Raman scattering light; the Raman scattering light is modulated to the frequency domain to form channelized Raman spectrum.

[0077] Embodiment 2

[0078] On the basis of embodiment 1, further comprising:

[0079] Further comprising: extracting polarized Raman spectrum from the channelized Raman spectrum.

[0080] Embodiment 3

[0081] On the basis of embodiment 2, further comprising:

[0082] The specific process of forming the channelized Raman spectrum is that the Raman scattering light passes through the achromatic quarter-wave plate 11, the high-order retarder 15 and the second linear polarizer 12 in turn to form the channelized Raman spectrum; wherein the fast-axis direction of the achromatic quarter-wave plate 11 is 0°; the fast-axis direction of the high-order retarder 15 is 45°, and the transmission axis direction of the second linear polarizer 12 is 0°.

[0083] The retardation of the high-order retarder 15 is two-thirds of the cutoff frequency of the Raman spectrum signal.

[0084] Embodiment 4

[0085] The specific process of extracting the polarized Raman spectrum from the channelized Raman spectrum is:

[0086] Transforming the channelized Raman spectrum from the time domain to the frequency domain;

[0087] The channelized Raman spectrum forms a low-frequency channel and two symmetrical high-frequency channels in the frequency domain;

[0088] Taking out the low-frequency channel and transforming it back from the frequency domain to the time domain to extract the spectral information;

[0089] The high frequency channel is taken out again, and the polarization information is extracted after being transformed from the frequency domain to the time domain and being phase-corrected;

[0090] The specific process is as follows:

[0091] Compared with the traditional Raman spectrometer, the channel polarization Raman spectrometer (CPRM) of the application modulates the polarization information to different channels in the frequency domain through a polarization modulation module, and then the polarization information is recorded by the spectrometer.

[0092] Analog modulation spectrum I modulated Can be expressed as

[0093]

[0094] In the formula: sigma is the wave number, cm -1 ; S1, S2 and S3 are linear polarization components, dimensionless; is a phase shift, rad; Introduced by a thick retarder; B is the birefringence coefficient of the retarder, dimensionless; d is the thickness of the retarder, cm;

[0095] The formula (5-1) is further written as

[0096]

[0097] In the formula: i is the imaginary part of a complex number;

[0098] According to the frequency shift property of Fourier transform, if a signal is multiplied by an exponential term in the time domain, a shift will occur in the frequency domain, therefore, the Fourier transform result of the channel modulation spectrum I modulated is written as

[0099] FT{I modulated}=C0+C -1 +C1 (5-3)

[0100] In the formula: FT{} represents the Fourier transform operation; C0 is a low-frequency channel containing the S0 signal, and C1 and C -1 are symmetrically distributed high-frequency channels, which save the information of S1 and S2. The three channels are separated from each other in the frequency domain, and can be taken out separately to do inverse Fourier transform, so as to extract S0, S1 and S2 respectively:

[0101] IFT{C0}=S0(σ) / 2 (5-4a)

[0102]

[0103]

[0104] where IFT{} represents the inverse Fourier transform operation; even if the retarders are made of the same material, there are still differences in the birefringence coefficients, so the calibration of the retardation of the retarder, i.e. the phase term in equation (5-4), is very important and directly related to the accurate demodulation of S1 and S2 components. In the calibration of the phase introduced by the retarder, a horizontally polarized polarizer is placed in the middle of the notch filter and the achromatic quarter-wave plate, so as to polarize the calibration light source to a known polarization state, at this time there is a transformation relationship of equation (5-5):

[0105] IFT{C 0,calibration}=S 0,calibration (σ) / 2 (5-5a)

[0106]

[0107]

[0108] where C 0,calibration , C 1,calibration , C 2,calibration are the channels in the calibration process; S 0,calibration , S 1,calibration are the polarization components of the calibration light source;

[0109] For the horizontally polarized calibration light, the S0 component and the S1 component are equal, and the S2 component is zero, at this time the calibrated exponential term can be calculated from the following equation:

[0110]

[0111]

[0112] Substituting equation (5-6) into equation (5-4), each polarization component can be calculated by the following equation:

[0113] S0(σ)=2*IFT{C0} (5-7a)

[0114] S1(σ)=2Re{IFT{C1}*IFT{C 0,calibration} / IFT{C 1,calibtration}} (5-7b)

[0115] S2(σ)=-2Im{IFT{C1}*IFT{C 0,calibration} / IFT{C 1,calibtration}}(5-7c)

[0116] where Re is the real part operation; Im is the imaginary part operation;

[0117] The phase calibration is only needed once before the experiment starts, then the inserted polarizer can be removed and the actual probing can be performed.

[0118] Embodiment 5

[0119] A channel spectral type polarized Raman spectrum measurement method, the method is as follows:

[0120] The incident laser is adjusted to be parallel light beam after collimation by a collimation mirror 1, and stray light other than the wavelength of the incident laser is filtered out by an ultra-narrow band-pass filter 2, and then the incident laser is changed to polarized incident laser by a first linear polarizer 3 and a half-wave plate 4 in sequence;

[0121] The polarized incident laser is transmitted to a trap wave beam splitter 6 after passing through a beam splitter 5, and then is reflected to a plane mirror 7, and the plane mirror 7 is reflected to a microscope objective 8, and is focused on a sample plane 9 by the microscope objective 8, and the polarized incident laser interacts with the sample plane 9 to generate Rayleigh scattering light and Raman scattering light; the Rayleigh scattering light is collected by the microscope objective 8, and then is reflected to the trap wave beam splitter 6 by the plane mirror 7;

[0122] The Raman scattering light is transmitted to the trap wave beam splitter 6, and then the residual laser is filtered out by a trap wave filter 10, and then is modulated into a channelized Raman spectrum by a polarization modulation module, is converged to the entrance of an optical fiber by an imaging lens 13, and finally is guided into a spectrometer by the optical fiber;

[0123] The Rayleigh scattering light is reflected to the beam splitter 5 by the trap wave beam splitter 6, and then is reflected to a plane array detector 14 to realize bright field imaging of the sample plane 9;

[0124] The incident laser is an incident laser with a wavelength of 785 nm, which is generated by a diode laser with a central wavelength of 785 nm.

[0125] Embodiment 6

[0126] A channel spectral type polarized Raman spectrometer, comprising a polarized laser generation system, a Raman light generation system, a Raman light collection system and a bright field imaging system connected in sequence; wherein,

[0127] The polarized laser generation system comprises a first linear polarizer 3 and a half-wave plate 4 arranged in sequence along an excitation light path of the incident laser;

[0128] The Raman light generation system comprises a beam splitter 5, a trap wave beam splitter 6, a plane mirror 7 and a microscope objective 8 arranged in sequence along a polarized incident excitation light path; and further comprises a sample, which is located at the focal point of the microscope objective 8;

[0129] The Raman light collection system includes a microscope objective 8, a plane mirror 7, a notch beam splitter 6, a notch filter 10, a polarization modulation module, and a collection module arranged in sequence. The polarization modulation module includes an achromatic quarter-wave plate 11, a higher-order retarder 15, and a second linear polarizer 12 arranged in sequence. The fast axis of the achromatic quarter-wave plate 11 is 0°, the fast axis of the higher-order retarder 15 is 45°, and the transmission axis of the second linear polarizer 12 is 0°. The collection module includes an imaging mirror 13 and an optical fiber arranged in sequence, with the optical fiber connected to the spectrometer.

[0130] The bright field imaging system includes a microscope objective 8, a plane mirror 7, a notch beam splitter 6, a beam splitter 5, a second imaging mirror 13, and an area array detector 14 arranged in sequence.

[0131] The beam splitter 5 is shared by the Raman light generation system and the bright field imaging system, and the microscope objective 8, the plane mirror 7, and the notch beam splitter 6 are shared by the Raman light generation system, the Raman light collection system, and the bright field imaging system.

[0132] The polarized laser generation system includes a collimating lens 1, an ultra-narrow bandpass filter 2, a first linear polarizer 3, and a half-wave plate 4 arranged sequentially along the excitation path of the incident laser.

[0133] Principle verification.

[0134] 1. Simulation measurement (taking the Raman spectrum of polypropylene fiber as an example)

[0135] The principle of the channel-type polarization Raman spectrometer was preliminarily verified through computer simulation, and the retardation amount of the higher-order retarder 15 was determined accordingly. The polypropylene micro-Raman spectra with different analysis directions were first measured using a conventional polarization Raman spectrometer, and then the retardation was determined according to S0 = I0 + I... 90 S1 = I0 - I 90 , and S2 = I 45 -I 135 The polarization components are derived from the relationship, and the simulated modulation spectrum is calculated from equation (5-1). Finally, the S0 component and the Fast Fourier Transform (FFT) results of the simulated modulation spectrum are calculated respectively, as follows: Figure 3 As shown;

[0136] The FFT transform results of the Raman spectrum of polypropylene fibers show that the S0 signal occupies only a small part of the central frequency domain, i.e., the low-frequency region. This signal can be preserved in the C1 and C2 regions by appropriately designing the delay amount (birefringent crystal material, thickness) of the high-order retarder 15. -1 The S1 and S2 signals in the channel can be well separated from the C0 channel in the frequency domain, thus making the polarization components separable in the frequency domain. In this invention, through the parameter design of the higher-order delayer 15, C1(C-1 The center distance between the C0 channel and the C0 channel is 2 / 3 times the Raman signal cutoff frequency. At this time, each channel has the same channel width, the signal distortion caused by the loss of high frequency signals is minimized, and the probability of frequency leakage and channel crosstalk between channels is minimized.

[0137] Figure 4 The results of demodulating the simulated modulation spectrum using the Fourier transform method are shown. The recovery residual of the polarization components of the polypropylene fiber is very small, indicating that each polarization component has been successfully demodulated from the simulated modulation spectrum. This provides preliminary proof of the correctness of the CPRM principle and the design of the 15 parameters of the high-order delayer.

[0138] 2. Experimental Measurement

[0139] Through the present invention Figure 2 The channel-type polarized Raman spectrometer shown was used to measure the same polypropylene fiber, such as... Figure 5 As shown, all the line Stokes parameters were successfully recovered according to the relationship in equation (5-7), proving the feasibility of CPRM.

[0140] Based on the above results, Figure 5 The curve trends in (b) and (c) Figure 5 The trends in the curves (e, f) are similar, where the laser polarization direction rotates by 90° while the sample orientation remains unchanged. However, when the laser direction remains unchanged while the sample orientation rotates by 90°, Figure 5 Comparison of the restored S2 signal in (i) Figure 5 (c) shows a completely opposite trend, with positive signals becoming negative and negative signals becoming positive, indicating that the polarization component of the polypropylene fiber changes with the sample orientation. This result is consistent with the measurement results obtained by conventional polarization Raman spectroscopy, cross-validating the correctness of CPRM.

[0141] The polypropylene fiber was then split in half, and one half was placed on aluminum foil and melted using an induction cooker. The melted polypropylene was measured using a CPRM, and the results are as follows. Figure 6 As shown, the results indicate that the polarization characteristics of the Raman signal of the melted polypropylene fiber depend on the polarization direction of the laser.

[0142] To quantitatively analyze the difference in polarization properties of polypropylene samples before and after melting, Table 1 lists the polarization characteristics of both samples at 973 cm⁻¹. -1 and 1167cm -1The results show the polarization angles at the Raman characteristic peaks. For polypropylene fibers, when the laser polarization direction is rotated from 0° to 90°, the polarization angles remain almost unchanged (-49.6°, -47.4° and -48.6°, -48.8°); however, when the sample is rotated, the polarization angles change from -49.6° to 41.7° and from -47.4° to 44.4°, respectively, with differences of 91.3° and 91.8°. For the molten polypropylene sample, when the laser polarization direction is rotated by 90°, the polarization angles also change by 89.6° and 91.0°, respectively, while the rotation of the sample has almost no effect on the polarization angles of the molten polypropylene sample. The results in Table 1 further demonstrate that the polarization angle of polypropylene fibers can be used to indicate the main distribution direction of the corresponding molecular bonds, and this property disappears when the internal crystal structure of the sample is destroyed (e.g., during melting). By utilizing the property that polarization angle can serve as an indicator of molecular orientation, it can be used to determine whether the molecules inside a sample (such as polypropylene) are arranged in an orderly manner and whether the crystal structure is intact. These properties largely reflect the mechanical properties of the material.

[0143] Table 1 Comparison of polarization angles of polypropylene fibers before and after melting

[0144]

[0145] In addition to acquiring single-point linearly polarized Raman spectral data, the CPRM also possesses imaging capabilities. In the CPRM experimental setup, the sample is placed on a displacement platform. By moving this platform, the sample plane 9 can be scanned sequentially, thereby achieving polarized Raman spectral imaging. In the CPRM's image processing mode, measurements were taken on a tooth sample, and its degree of linear polarization was calculated, as shown below. Figure 7 As shown. The measured tooth sample can be divided into two parts, the upper left and lower right corners, representing the tooth matrix and enamel respectively. These are clearly separated by a dividing line in the grayscale image, but the grayscale images of the two regions are difficult to distinguish with the naked eye. PO4 at 959 cm⁻¹ -2 In the polarization degree image of the peaks, the polarization degree of the enamel is significantly greater than that of the tooth matrix, and the two regions show high contrast in the polarization degree image, achieving good differentiation. Polarization Raman imaging of tooth samples verifies that polarization information can effectively improve image contrast, thereby enabling target recognition and classification.

Claims

1. A method of channel spectral type polarization Raman spectroscopy, characterized by, The method is as follows: the incident laser is changed into polarized incident laser; the polarized incident laser is focused on the sample plane (9) to generate Raman scattering light by Raman effect; the Raman scattering light is modulated to the frequency domain by polarization to form a channelized Raman spectrum; and then the polarized Raman spectrum is extracted from the channelized Raman spectrum; The specific process of forming the channelized Raman spectrum is as follows: The Raman scattering light sequentially passes through the achromatic quarter-wave plate (11), the high-order retarder (15) and the second linear polarizer (12) to form the channelized Raman spectrum; wherein the fast axis direction of the achromatic quarter-wave plate (11) is 0°; the fast axis direction of the high-order retarder (15) is 45°, and the retardation of the high-order retarder (15) is two-thirds of the cutoff frequency of the Raman spectrum signal; and the transmission axis direction of the second linear polarizer (12) is 0°; The specific process of extracting the polarized Raman spectrum from the channelized Raman spectrum is as follows: The channelized Raman spectrum is transformed from the time domain to the frequency domain; The channelized Raman spectrum forms a low-frequency channel and two symmetrical high-frequency channels in the frequency domain; The low-frequency channel is taken out and transformed from the frequency domain back to the time domain to extract the spectral information; The high-frequency channel is taken out and transformed from the frequency domain back to the time domain, and then the phase correction is performed to extract the polarization information.

2. The method of claim 1, wherein the method is a channel-spectroscopic polarization Raman spectroscopy method. The method is as follows: The incident laser is collimated by the collimating mirror (1) to form a parallel light beam, the stray light other than the wavelength of the incident laser is filtered out by the ultra-narrow band-pass filter (2), and then the incident laser sequentially passes through the first linear polarizer (3) and the half-wave plate (4) to change into polarized incident laser; The polarized incident laser transmits through the beam splitter (5), is reflected to the plane mirror (7) after transmitting through the trap wave beam splitter (6), is reflected to the microscopic objective (8) by the plane mirror (7), is focused on the sample plane (9) by the microscopic objective (8), and generates Rayleigh scattering light and Raman scattering light after the polarized incident laser interacts with the sample plane (9); the Rayleigh scattering light and the Raman scattering light are collected by the microscopic objective (8), are reflected to the trap wave beam splitter (6) by the plane mirror (7), and then the Raman scattering light transmits through the trap wave beam splitter (6), is filtered by the trap wave filter (10) to remove the residual laser, is modulated into a channelized Raman spectrum by the polarization modulation module, is converged to the entrance of the optical fiber by the imaging lens (13), and finally is introduced into the spectrometer by the optical fiber; The Rayleigh scattering light is reflected to the beam splitter (5) by the trap wave beam splitter (6), and then is reflected to the area array detector (14) to realize bright field imaging of the sample plane (9). The incident laser is a 785nm wavelength incident laser generated by a diode laser with a central wavelength of 785nm.

3. The method of claim 2, wherein the method is a channel-spectrally-polarized Raman spectroscopy method. The system comprises a polarized laser generation system, a Raman light generation system, a Raman light collection system and a bright field imaging system connected in sequence; wherein 4. A channel-spectrally-polarization-resolved Raman spectrometer for implementing the channel-spectrally-polarization-resolved Raman spectroscopy method according to claim 3, characterized in that The polarized laser generation system comprises the first linear polarizer (3) and the half-wave plate (4) arranged in sequence along the excitation light path of the incident laser; The Raman light generation system comprises the beam splitter (5), the trap wave beam splitter (6), the plane mirror (7) and the microscopic objective (8) arranged in sequence along the polarized incident excitation light path; and further comprises a sample, which is located at the focal point of the microscopic objective (8). ​ The Raman light collection system includes a microscope objective (8), a plane mirror (7), a notch beam splitter (6), a notch filter (10), a polarization modulation module, and a collection module arranged in sequence. The polarization modulation module includes an achromatic quarter-wave plate (11), a higher-order retarder (15), and a second linear polarizer (12) arranged in sequence. The fast axis of the achromatic quarter-wave plate (11) is 0°, the fast axis of the higher-order retarder (15) is 45°, and the transmission axis of the second linear polarizer (12) is 0°. The collection module includes an imaging mirror (13) and an optical fiber arranged in sequence, with the optical fiber connected to the spectrometer. The bright field imaging system includes a microscope objective (8), a plane mirror (7), a notch beam splitter (6), a beam splitter (5), an imaging mirror (13), and an area array detector (14) arranged in sequence. The beam splitter (5) is shared by the Raman light generation system and the bright field imaging system, and the microscope objective (8), the plane mirror (7), and the notch beam splitter (6) are shared by the Raman light generation system, the Raman light collection system, and the bright field imaging system.

5. The channel spectropolarimetric Raman spectrometer of claim 4, wherein, The polarized laser generation system includes a collimating lens (1), an ultra-narrow bandpass filter (2), a first linear polarizer (3), and a half-wave plate (4) arranged sequentially along the excitation path of the incident laser.

Images