A method for measuring longitudinal polarization Raman signals based on vector polarization beam

Abstract

The present invention discloses a method for measuring longitudinal polarized Raman signals based on a vector polarized light beam, comprising the following steps: 1) building a Raman spectroscopy system capable of generating angular polarized light and radial polarized light as excitation light sources; 2) using a Raman signal correction system of an isotropic sample; 3) using a single crystal silicon sample verification system; 4) using angular polarized light and radial polarized light as excitation light sources respectively to measure the Raman signal of a sample to be measured; 5) using the measured data in combination with theoretical calculations to obtain a Raman signal excited by the longitudinal polarized light. The present invention designs a method for detecting Raman signals excited by the longitudinal polarized light based on the relationship between the electric field distributions of the angular polarized light and the radial polarized light in the focal region, and the method solves the problem that the Raman signals excited by the longitudinal polarized light cannot be directly and accurately measured at present.

Description

Technical Field

[0001] The invention belongs to the field of optical technology, and in particular relates to a method for measuring a longitudinal polarization Raman signal based on a vector polarization light beam. Background Art

[0002] Raman spectroscopy uses photons as probes, and has the advantages of non-contact, non-destructive and high sensitivity. It is an effective tool for rapid and real-time detection of material structure and microstructure, as well as the interaction between phonons and other elementary excitations. It can be used to understand the defects inside the crystal, lattice distortion and phase transition, etc. In addition to providing general chemical identification information that conventional Raman can provide, polarized Raman spectroscopy can also detect information about molecular orientation and chemical bond vibration symmetry.

[0003] At present, polarized Raman usually uses linearly polarized light for excitation. The polarization direction of the excitation light is perpendicular to the propagation direction of the light beam and parallel to the sample surface. It can effectively detect samples with uniform molecular orientation and parallel to the sample surface, but it is not conducive to detecting samples with molecular orientation perpendicular to the propagation direction of the light beam. Under the commonly used backscattering experimental conditions, if you need to measure a vertically oriented sample, you need to change the cutting direction of the sample or rotate the sample by a certain angle. Strong focusing of a radially polarized light beam can theoretically produce a strong longitudinal polarization light field at the focus, which can be used to excite the longitudinally polarized Raman signal, but there is still a non-negligible transverse polarization component in the focal area, which will interfere with the measurement of the longitudinally polarized Raman signal. Summary of the invention

[0004] The purpose of the present invention is to solve the above problems and provide a method for measuring a longitudinal polarized Raman signal based on a vector polarized beam, comprising the following steps:

[0005] S1: Build a Raman spectroscopy system. The excitation light source of the Raman spectroscopy system can generate angular polarized light and radial polarized light, and the polarization states of the angular polarized light and radial polarized light can be adjusted arbitrarily;

[0006] S2: Use an isotropic sample to calibrate the Raman spectroscopy system until the Raman signal intensities of azimuthally polarized light and radially polarized light at different angles are the same;

[0007] S3: Use a single crystal silicon sample to verify whether the result of the Raman spectroscopy system in S2 is correct;

[0008] S4: using angular polarized light and radial polarized light as excitation light sources to detect the Raman signal of the sample to be tested, and obtaining measurement data;

[0009] S5: Based on the measured data, the Raman signal excited by the longitudinal polarized light is obtained by calculation.

[0010] Further, in S1, the Raman spectroscopy system includes: a narrow linewidth laser, a polarization converter, a dichroic mirror, an analyzer, a spectral detector, an objective lens, a sample stage and a sample, and the polarization converter is used to realize the conversion between angular polarized light and radial polarized light;

[0011] A narrow linewidth laser emits a single-mode Gaussian collimated beam, which is converted into a vector polarized beam through a polarization converter. The vector polarized beam is reflected to the objective lens through a dichroic mirror and focused on the sample placed on the sample stage. The vector polarized beam irradiates the sample to excite the Raman signal and returns along the original optical path. After passing through the dichroic mirror and the analyzer in sequence, it enters the spectral detector, which generates spectral data.

[0012] Furthermore, during the process of the polarization converter converting the angular polarized light and the radial polarized light, the laser power emitted by the narrow linewidth laser remains unchanged.

[0013] Furthermore, in S2, the correction process of the Raman spectroscopy system includes the following steps:

[0014] S21: Use angularly polarized light to excite the isotropic sample, rotate the polarizer by a certain angle to one circle, and record the Raman signal at each rotation angle during one circle of the polarizer;

[0015] S22: Use radially polarized light to excite the isotropic sample, rotate the analyzer by the same angle for one rotation, and record the Raman signal at each rotation angle during one rotation of the analyzer;

[0016] S23: Check whether the Raman signal intensities of the analyzers in S21 and S22 at different angles are the same. If not, return to S1 and adjust the optical path until the Raman signal intensities of the samples in S21 and S22 at different angles are the same.

[0017] Furthermore, the certain angle is less than or equal to 18°.

[0018] Further, in S3, by using single crystal silicon <110> Repeat the measurements of S21 and S22 for the crystal surface sample, and calculate the measurement results to obtain the ratio of the transverse polarized light intensity to the focused radial polarized light η r , the calculation method is as follows: Change η r The value of The value of changes with the sample rotation angle θ is the smallest, where I r (θ) and They are the focused radially polarized light and the Raman signal excited by the radially polarized light at different sample rotation angles θ.

[0019] Further, in S5, the Raman signal of the sample excited by pure longitudinal polarized light is obtained by the following process: the sample to be tested is excited by radial polarized light and angular polarized light respectively and the Raman spectrum A is measured. r and The combined η r The value of The Raman spectrum of the sample to be tested excited by pure longitudinal polarized light is obtained.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. The technical solution of the present invention realizes the measurement of Raman signals excited by longitudinally polarized light, which is currently unachievable by other polarization measurement methods.

[0022] 2. The measurement method in the technical solution of the present invention can quantitatively calibrate the system and quantitatively verify the accuracy of the system; although there are reports on using vector beams to measure Raman signals excited by longitudinal polarized light, they are all qualitative measurements. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the experimental device of the Raman spectroscopy system of the present invention;

[0024] Figure 2 (a) and (b) are respectively <110> (a) The relationship between the calculated Raman signal and the rotation angle of the analyzer when the single crystal silicon is excited by azimuthal polarization and radial polarization; (b) The relationship between the calculated Raman signal and the rotation angle of the analyzer when the single crystal silicon is excited by pure longitudinal polarization;

[0025] Figure 3 For the present invention <110> The relationship curve between the experimentally measured Raman signal and the analyzer rotation angle of planar single crystal silicon under the excitation of azimuthal polarization and radial polarization light, as well as the relationship curve between the Raman signal excited by pure longitudinal polarization light and the analyzer rotation angle calculated from these two curves.

[0026] Among them, 1: narrow linewidth laser; 2: angular / radial polarization converter; 3: dichroic mirror; 4: analyzer; 5: spectral detector; 6: objective lens; 7: sample; 8: sample stage. DETAILED DESCRIPTION

[0027] A method for measuring a longitudinal polarized Raman signal based on a vector polarized light beam of the present invention will be described in more detail below in conjunction with a schematic diagram, wherein a preferred embodiment of the present invention is shown. It should be understood that those skilled in the art can modify the present invention described herein while still achieving the beneficial effects of the present invention. Therefore, the following description should be understood as being widely known to those skilled in the art and not as a limitation to the present invention.

[0028] In the description of the present invention, it should be noted that directional words, such as the terms "center", "lateral", "longitudinal", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", etc., indicating directions and positional relationships are based on the directions or positional relationships shown in the accompanying drawings, which are only for the convenience of narrating the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and cannot be understood as limiting the specific scope of protection of the present invention.

[0029] A method for measuring a longitudinally polarized Raman signal based on a vector polarized beam comprises the following steps:

[0030] 1) Build a Raman spectroscopy system, the excitation light source of which can generate angular polarized light and radial polarized light, and the polarization states of the angular polarized light and radial polarized light can be adjusted arbitrarily. Figure 1 As shown, it includes: a narrow line width laser 1, a polarization converter, a dichroic mirror 3, an analyzer 4, a spectrum detector 5, an objective lens 6, a sample stage 8 and a sample 7. The polarization converter is an angular / radial polarization converter 2, which is used to realize the conversion between angular polarized light and radial polarized light, and during the conversion process, the laser power needs to remain unchanged;

[0031] 2) Use isotropic samples to calibrate the Raman spectroscopy system until the Raman signal intensities of azimuthal polarized light and radial polarized light at different angles are the same, including:

[0032] 21) Using angularly polarized light to excite the isotropic sample, rotating the analyzer 4, each rotation angle is no more than 18°, for one circle, and recording the Raman signal at each rotation angle of the analyzer 4 during one circle;

[0033] 22) Using radially polarized light to excite the isotropic sample, rotating the polarizer 4 in the same manner to rotate one circle, and recording the Raman signal at each rotation angle of the polarizer 4 during one circle;

[0034] 23) Check whether the Raman signal intensities of the analyzer 4 at different angles in S21 and S22 are the same. If not, return to S1 and adjust the optical path until the Raman signal intensities of the samples at different angles in S21 and S22 are the same;

[0035] 3) Using a single crystal silicon sample to check whether the result of the Raman spectroscopy system in S2 is correct, specifically by measuring in the same manner as steps S21-S22, and verifying the accuracy of the system by calculating the measurement results;

[0036] The measurement process is: change η r The value of The value of changes with the sample rotation angle θ is the smallest, where I r (θ) and They are the focused radially polarized light and the Raman signal excited by the radially polarized light at different sample rotation angles θ.

[0037] 4) using angular polarized light and radial polarized light as excitation light sources to detect the Raman signal of the sample to be tested and obtain measurement data;

[0038] 5) Based on the measured data, the Raman signal excited by the longitudinal polarized light is obtained by calculation.

[0039] The calculation process is as follows: radially polarized light and angularly polarized light are used to excite the sample to be tested and the Raman spectrum A is obtained. r and The combined η r The value of The Raman spectrum of the sample to be tested excited by pure longitudinal polarized light is obtained.

[0040] It should be emphasized that the Raman spectroscopy system needs to generate relatively ideal angular polarization and radial polarization light to avoid deviation in the results; before measuring the sample to be tested, the Raman signal of the isotropic sample should be measured first, and accurate theoretical calculations should be performed based on the experimental parameters to obtain accurate Raman signals excited by longitudinal polarization light. This sequential operation can better ensure accurate results.

[0041] Example 1

[0042] refer to Figure 1 , the narrow linewidth laser 1 generates a single-mode Gaussian collimated light beam, which is converted into a vector polarized light beam after passing through the angular / radial polarization converter 2. Then the light beam is reflected by the dichroic mirror 3 to the objective lens 6 and focused on the sample 7 placed on the rotating sample stage 8. The excited Raman signal returns along the original light path, passes through the dichroic mirror 3 and the analyzer 4, and reaches the spectral detector 5 to generate spectral data. After the system is built, it is first necessary to adjust the position and angle of the angular / radial polarization converter 2 and the objective lens 6 by observing the shape of the light spot, so that the light spot after passing through the objective lens has central symmetry. Then use an isotropic sample, use angular and radial polarized light to excite the sample respectively, rotate the analyzer, and record the intensity of the same Raman peak at different analyzer angles. Check whether the Raman signal intensities at different analyzer angles are the same when excited by two polarized lights. If different, adjust the polarization converter until the signal intensity is the same. Next, use the crystal plane as <110> The single crystal silicon sample was excited by azimuthal and radial polarized light, and the polarizer was rotated 4 times to record 521 cm -1The intensity of the nearby Raman peaks at different angles of the analyzer 4 is used to obtain a curve of Raman signal intensity varying with angle. The curve corresponding to the radial polarized light is subtracted from the product of the curve of the angular polarized light and a constant, and the value of the constant is changed until the obtained curve becomes a horizontal straight line, and the value of the constant is recorded at this time. Finally, the sample to be tested is placed on the sample stage 8, and is excited by angular polarized light and radial polarized light respectively, and the analyzer 4 is removed from the light path, and the Raman spectrum is recorded. The Raman spectrum obtained by excitation with radial polarized light is subtracted from the product of the Raman spectrum obtained by excitation with angular polarized light and the constant, and the Raman spectrum excited by pure longitudinal polarized light is obtained.

[0043] Example 2

[0044] Through theoretical calculation, the crystal plane is obtained as <110> The single crystal silicon sample is excited by azimuthal, radial and longitudinal polarized light respectively. The Raman signal intensity of the rotating polarizer 5 varies with the angle of the polarizer 4, as shown in Figure 2 (ac) shown. Figure 2 (c) It can be achieved through Figure 2 (b) The curve minus Figure 2 The product of the curve in (a) and a constant is obtained, which proves that the method proposed in the present invention is feasible.

[0045] Example 3

[0046] Figure 3 The crystal plane measured in the experiment is shown as <110> The graphs show the Raman signal of the single crystal silicon sample under the excitation of azimuthal and radial polarized light as the analyzer angle changes by 4 degrees. The graphs of the Raman signal excited by longitudinal polarized light calculated from these two curves are also shown. It can be seen that the calculated results are basically consistent with the theoretical calculations, which proves that the method proposed in the present invention for measuring longitudinal polarized Raman signals based on vector polarized light beams is feasible and effective.

[0047] The above is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any technician in the relevant technical field, without departing from the scope of the technical solution of the present invention, makes any form of equivalent replacement or modification to the technical solution and technical content disclosed in the present invention, which does not depart from the content of the technical solution of the present invention and still falls within the protection scope of the present invention.

Claims

1. A method for measuring longitudinal polarization Raman signals based on a vector polarization beam, characterized in that: The steps include: S1: Building a Raman spectroscopy system, wherein the excitation light source of the Raman spectroscopy system can generate angularly polarized light and radially polarized light, and the polarization states of the angularly polarized light and radially polarized light can be adjusted arbitrarily; S2: Use an isotropic sample to calibrate the Raman spectroscopy system until the Raman signal intensities of azimuthally polarized light and radially polarized light at different angles are the same; S3: Using a single crystal silicon sample to test whether the result of the Raman spectroscopy system in S2 is correct; S4: using angular polarized light and radial polarized light as excitation light sources to detect the Raman signal of the sample to be tested, and obtaining measurement data; S5: Based on the measurement data, obtaining a Raman signal excited by the longitudinal polarized light by calculation; In S1, the Raman spectroscopy system includes: a narrow linewidth laser, a polarization converter, a dichroic mirror, an analyzer, a spectral detector, an objective lens, a sample stage and a sample, and the polarization converter is used to realize the conversion between angular polarized light and radial polarized light; During the conversion of angular polarized light and radial polarized light by the polarization converter, the laser power emitted by the narrow linewidth laser remains unchanged; In S2, the correction process of the Raman spectroscopy system includes the following steps: S21: Use angularly polarized light to excite the isotropic sample, rotate the polarizer by a certain angle to one circle, and record the Raman signal at each rotation angle during one circle of the polarizer; S22: Use radially polarized light to excite the isotropic sample, rotate the analyzer by the same angle for one rotation, and record the Raman signal at each rotation angle during one rotation of the analyzer; S23: Check whether the Raman signal intensities of the analyzers in S2 and S3 at different angles are the same. If not, return to S1 and adjust the optical path until the Raman signal intensities of the samples in S2 and S3 at different angles are the same. In S3, single crystal silicon <110> Repeat the measurements of S21 and S22 for the crystal surface sample, and calculate the measurement results to obtain the ratio of the transverse polarized light intensity to the focused radial polarized light η r , the calculation method is as follows: Change η r The value of The value of changes with the sample rotation angle θ is the smallest, where I r (θ) and They are the focused radial polarized light and the Raman signal excited by the radial polarized light at different sample rotation angles θ; In S5, the Raman signal of the sample excited by pure longitudinal polarized light is obtained by the following process: the sample to be tested is excited by radial polarized light and angular polarized light respectively and the Raman spectrum A is obtained by measuring r and The combined η r The value of The Raman spectrum of the sample to be tested excited by pure longitudinal polarized light is obtained.

2. The method for measuring longitudinal polarization Raman signals based on vector polarization beam according to claim 1, characterized in that: The narrow linewidth laser emits a single-mode Gaussian collimated beam, which is converted into a vector polarized beam by the polarization converter. The vector polarized beam is reflected to the objective lens by the dichroic mirror and focused on the sample placed on the sample stage. The vector polarized beam irradiates the sample to excite the Raman signal and returns along the original optical path. After passing through the dichroic mirror and the analyzer in sequence, it enters the spectral detector, and the spectral detector generates spectral data.

3. The method for measuring longitudinal polarization Raman signals based on vector polarization beam according to claim 1, characterized in that: The certain angle is less than or equal to 18°.

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