Second harmonic characterization system based on phase code division multiple access

Abstract

The invention relates to a second harmonic characterization system based on phase code division multiple access, and the system comprises an incident light path assembly which is used for carrying out the polarization and phase code division multiple access modulation of N paths of signal light beams after laser pulse beam splitting, obtaining N signal light beams coded by phase addresses, respectively focusing the N signal light beams, irradiating a sample on a sample stage, and reflecting N SHG signal light beams; the emergent light path assembly is used for receiving N signal light beams of the SHG, and performing collimation, polarization detection, light filtering and focusing respectively to obtain N detection light beams of the SHG; the reference light path assembly is used for performing polarization, frequency doubling, polarization detection, light filtering, optical path control and focusing on one reference light beam after main laser pulse beam splitting to form a reference light beam after frequency doubling; the N detection light beams and the reference light beam are respectively subjected to coupling, coherent detection, beam splitting and phase address code demodulation, and N-path SHG characterization is detected. According to the invention, multi-thread detection is realized, and the second harmonic optical characterization performance is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of nonlinear optical characterization, and in particular relates to a second harmonic characterization system based on phase code division multiple access. Background Art

[0002] Second harmonic generation (SHG) is a nonlinear optical microscopy characterization technique developed in recent years that produces second-order polarization by irradiating materials with high-intensity lasers. Among many characterization methods, second harmonics has demonstrated its ability to characterize the electric field and structural properties of material interfaces due to its non-destructive testing, high stability, and simple operation. For example, second harmonic characterization technology can be used to locate and identify structural defects such as stacking faults and dislocations in SiC wafers, and to characterize non-uniform strain information in materials. At the same time, time-dependent second harmonics can obtain information on interface state density and fixed oxide charge.

[0003] Currently, in the field of wafer characterization, second harmonic characterization technology is limited by certain inherent properties of its equipment. These devices mainly use single-beam technology to accurately characterize a single point on the surface of the material. Although this method can provide highly accurate data, its main limitations are that the characterization speed is slow and only a single point can be analyzed. This limitation has hindered the understanding of the comprehensive characteristics of the material to a certain extent, and there is a lack of efficiency due to the inability to effectively integrate and analyze multi-point data.

[0004] In order to more fully understand the characteristics of the material, it is particularly important to perform SHG characteristic analysis on the entire row or entire area of ​​the wafer. This analysis method not only provides detailed information on a specific point, but also reflects the properties of the material as a whole, which is crucial for a comprehensive evaluation of the material's characteristics. Therefore, developing a device that can perform SHG characterization on multiple points at the same time is of great significance to improving the overall characterization efficiency. Summary of the invention

[0005] In view of the above analysis, the present invention aims to disclose a second harmonic characterization system based on phase code division multiple access, which can characterize multiple points of a material at the same time, help to comprehensively evaluate the material, and improve the characterization efficiency of the second harmonic.

[0006] The invention discloses a second harmonic characterization system based on phase code division multiple access, comprising: an incident light path component, an output light path component, a reference light path component, a sample and a sample stage;

[0007] The incident light path component is used to polarize and phase code division multiple access modulate the N signal light beams after the main laser pulse is split in the incident light path, so as to obtain N signal light beams carrying phase address codes, which are respectively focused and irradiated on the sample on the sample stage, and reflect N SHG signal light beams;

[0008] An outgoing optical path component is used to receive N SHG signal light beams, and obtain N SHG detection light beams after collimation, polarization analysis, filtering and focusing respectively;

[0009] A reference optical path component is used to polarize, frequency-double, analyze, filter, control the optical path and focus a reference beam after the main laser pulse is split to form a reference beam for SHG;

[0010] After coupling and coherent detection of N SHG-carrying detection beams and SHG reference beams, signal splitting and N-channel phase address code demodulation are performed, and N-channel SHG characterizations carrying sample defect information are detected.

[0011] Furthermore, the incident light path assembly includes: a laser, a beam splitter, a polarizer group, a phase modulator group, a signal generator and a transmitting end objective lens group; wherein,

[0012] The laser is used to generate a main laser pulse;

[0013] The beam splitter is used for laser multi-path beam splitting to split the main laser pulse into N signal beams and 1 reference beam;

[0014] The polarizer group is used to adjust the polarization state of the fundamental frequency light of the N signal light beams to obtain a polarization angle that meets the test requirements;

[0015] The signal generator is used to generate N mutually orthogonal pseudo-random sequences required for phase code division multiple access encoding;

[0016] The phase modulator group is used to perform phase modulation on each signal beam output by the polarizer group using a pseudo-random sequence generated by the signal generator to form N signal beams carrying phase address codes;

[0017] The transmitting end objective lens group is used to focus the N signal light beams carrying the phase address code output by the phase modulator group respectively, so that the N signal light beams are focused to the corresponding positions on the sample respectively; and reflect the N SHG signal light beams.

[0018] Furthermore, the output optical path assembly includes a receiving end objective lens group, an analyzer group, a filter, a receiving end coupling lens group and a signal collector; wherein,

[0019] The receiving end objective lens group is used to collimate the N SHG signal light beams reflected by the sample respectively;

[0020] The polarizer group is used to select the polarization states of the N light beams output by the receiving end objective lens group respectively, so as to output the light beams whose polarization angles meet the test requirements;

[0021] The filter is used to filter the N light beams output by the analyzer group to remove the fundamental frequency light;

[0022] The receiving end coupling lens group is used to focus the N light beams output by the filter to the receiving position of the signal collector respectively;

[0023] The signal collector is used to perform coherent detection on the signal light beam and the reference light beam entering the receiving position and output an electrical signal.

[0024] Furthermore, the reference light path assembly includes: a reference light polarizer, a frequency doubling crystal, a reference light objective lens, a reference light analyzer, a reference light filter, an optical path controller, and a reference light coupling lens group;

[0025] The reference light polarizer is used to adjust the polarization state of the fundamental frequency light of a reference light beam output from the beam splitter so that the polarization angle of the reference light beam is the same as the polarization angle of the signal light beam;

[0026] The frequency doubling crystal is used to frequency-double the light beam output by the reference light polarizer to obtain a reference light beam for SHG;

[0027] The reference light objective lens is used to collimate the light beam output by the frequency doubling crystal;

[0028] The reference light analyzer is used to select the polarization state of the light beam output by the reference light objective lens, and output the light beam with the same polarization angle as the signal light beam;

[0029] The reference light filter is used to filter the light beam output by the reference light analyzer to remove the fundamental frequency light;

[0030] The optical path controller is used to control the optical path of the light beam output by the reference light filter so that the optical path of the reference light beam entering the signal collector is consistent with the optical path of the outgoing light beam;

[0031] The reference light coupling lens is used to focus the light beam output by the optical path controller, and focuses the light beam output by the optical path controller to the receiving position of the signal collector for subsequent coherent detection.

[0032] Furthermore, the reference optical path component further includes: a first optical path adjustment component and a second optical path adjustment component;

[0033] The first optical path adjustment component is used to adjust the optical path of a reference light beam output by the beam splitter to align with the reference light polarizer, so as to adjust the polarization state of the reference light beam;

[0034] The second optical path adjustment component is used to adjust the optical path of the light beam output by the reference light filter to align with the optical path controller to perform optical path control of the reference light beam.

[0035] Furthermore, the second harmonic characterization system also includes a processing control unit, which is connected to the signal collector; used to output an electrical signal after coherent detection of the signal collector, perform power amplification, signal beam splitting, phase locking, and N-channel phase address code demodulation, and detect N-channel second harmonic signals carrying sample defect information;

[0036] The processing control unit includes: a power division amplifier, a phase address code demodulator and a digital control terminal;

[0037] The power splitter amplifier is used to amplify the power of the signal and split the signal; outputting N channels of power-amplified signals;

[0038] The phase address code demodulator is used to perform address code demodulation on the N-channel signals after power amplification respectively using the same N-channel code division multiple access pseudo-random sequence as that in the incident light path component, so as to obtain N-channel demodulated signals corresponding to the positions where the N signal light beams irradiate the samples;

[0039] The digital control terminal is used to perform frequency discrimination on N demodulated signals respectively to obtain N SHG characterizations carrying sample defect information.

[0040] Furthermore, a phase-locked circuit is connected between the power divider amplifier and the phase address code demodulator in the processing control unit; the processing control unit and the incident light path component share a signal generator;

[0041] The phase-locked circuit is used to phase-lock N signals respectively; the starting phase deviations of the locked detection signals and the reference signals are input into the signal generator, and the phases of the code division multiple access pseudo-random sequences output by the signal generator are adjusted so that the phase deviations of the collected signals and the incident end are 0, that is, the starting times of the various optical paths are the same to ensure coherence; after address code demodulation of the signals output by the phase-locked circuit and the code division multiple access pseudo-random sequences generated by the signal generator with the phases adjusted, N demodulated signals corresponding to the positions of the samples irradiated by the N signal light beams are obtained.

[0042] Furthermore, the numerical control terminal also converts one of the N demodulated signals into a corresponding control voltage after real-time signal amplitude acquisition by a high-precision ADC. The control voltage is amplified by a high-voltage amplifier and output to an optical path controller; the optical path controller is a piezoelectric optical path controller; the piezoelectric ceramics in the optical path controller are deformed under high-voltage drive, pushing the reflector in the optical path controller to move, thereby adjusting the optical path of the reference beam, adjusting the coherence state of the signal beam and the reference beam, and achieving the best coherence state;

[0043] The adjustment steps of the optical path of the reference beam are as follows:

[0044] 1) Get the current signal amplitude value and control voltage value;

[0045] 2) Apply a small voltage disturbance;

[0046] 3) Compare the signal amplitude before and after the disturbance;

[0047] 4) If the amplitude increases, maintain the disturbance direction;

[0048] 5) If the amplitude decreases, change the disturbance direction;

[0049] 6) Iterate until the maximum value is reached.

[0050] Furthermore, it also includes: an arc guide rail, an incident arm and an exit arm;

[0051] The arc guide is located directly above the sample stage; the incident arm and the exit arm are slidably assembled on the arc guide, and both can slide on the arc guide around the sample stage;

[0052] The incident arm is the supporting structure of the incident light path component, and the output arm is the supporting structure of the output light path component. By controlling the positions of the incident arm and the output arm on the arc guide rail, the incident angle of the signal light beam incident on the sample is determined, and the output light path component is located in the reflected light beam of the sample, thereby realizing sample detection at the set incident angle.

[0053] Further, the sample stage is provided with a motion module to move the position of the sample in space, so that the laser can characterize the entire area of ​​the sample;

[0054] The motion module includes: an XY plane motion module and a rotation module around the Z axis; the XY motion module is used to adjust the position of the material under test so that the second harmonic multi-threaded detection system can complete step scanning during operation; the rotation module around the Z axis allows the material under test to rotate around the detection center point, which is used to adjust the azimuth angle during the detection process and obtain the dependence of the SHG of the material under test on the azimuth angle.

[0055] The present invention can achieve one of the following beneficial effects:

[0056] Compared with the existing second harmonic characterization system, the second harmonic characterization system based on phase code division multiple access of the present invention can simultaneously perform second harmonic characterization of multiple points of the material to be detected, effectively improving the characterization efficiency of the second harmonic characterization system.

[0057] In addition, in the multi-threaded second harmonic characterization system, the sample stage carrying the material to be tested is equipped with a motion module, which can make the sample stage and the material to be tested carried by it move in multiple dimensions, including movement in the x, y, and z directions and 360-degree rotation with the normal direction of the xy plane as the axis, thereby changing the azimuth angle of the incident light. The arc guide rail above the sample stage can control the incident angle of the fundamental frequency light, and the polarizer group of the incident arm adjusts the polarization angle of the fundamental frequency light to provide the polarization angle required for the test.

[0058] In summary, the various devices in the multi-threaded second harmonic characterization system cooperate with each other to realize the detection of azimuth angle, incident angle and polarization angle dependence in second harmonic characterization. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] The accompanying drawings are only used for the purpose of illustrating specific embodiments and are not to be considered as limiting the present invention. In the entire drawings, the same reference symbols represent the same components;

[0060] Figure 1 It is a schematic diagram of the connection components of a second harmonic characterization system based on phase code division multiple access in an embodiment of the present invention;

[0061] Figure 2 is an optical path and signal flow chart of a second harmonic characterization system in an embodiment of the present invention;

[0062] Figure numerals: 1. Laser, 2. Laser multi-way beam splitter, 3. Polarizer group, 4. Phase controller group, 5. Transmitter objective lens group, 6. Sample to be tested, 7. Sample stage and its motion module, 8. Receiving objective lens group, 9. Analyzer group, 10. Filter, 11. Receiving coupling lens group, 12. Signal collector, 13. Signal generator, 14. Arc guide, 15. Reflector, 16. Reference light polarizer, 17. Frequency doubling crystal, 18. Reference light objective lens, 19. Reference light analyzer, 20. Reference light filter, 21. Optical path controller, 22. Reference light coupling lens group. DETAILED DESCRIPTION

[0063] The preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used to illustrate the principles of the present invention together with the embodiments of the present invention.

[0064] Embodiment 1

[0065] One embodiment of the present invention discloses a second harmonic characterization system based on phase code division multiple access, such as Figure 1 As shown, it includes: an incident light path component, an exit light path component, a reference light path component, a sample and a sample stage;

[0066] The incident light path component is used to polarize and phase code division multiple access modulate the N signal light beams after the main laser pulse is split in the incident light path, so as to obtain N signal light beams carrying phase address codes, which are respectively focused and irradiated on the sample on the sample stage, and reflect N SHG signal light beams;

[0067] An outgoing optical path component is used to receive N SHG signal light beams, and obtain N SHG detection light beams after collimation, polarization analysis, filtering and focusing respectively;

[0068] A reference optical path component is used to polarize, frequency-double, analyze, filter, control the optical path and focus a reference beam after the main laser pulse is split to form a reference beam for SHG;

[0069] After coupling and coherent detection of N SHG-carrying detection beams and SHG reference beams, signal splitting and N-channel phase address code demodulation are performed, and N-channel SHG characterizations carrying sample defect information are detected.

[0070] Specifically, the incident light path component includes: a laser, a beam splitter, a polarizer group, a phase modulator group, a signal generator and a transmitting end objective lens group; wherein,

[0071] The laser is used to generate a main laser pulse;

[0072] The beam splitter is used for laser multi-path beam splitting to split the main laser pulse into N signal beams and 1 reference beam;

[0073] The polarizer group is used to adjust the polarization state of the fundamental frequency light of the N signal light beams to obtain a polarization angle that meets the test requirements;

[0074] The signal generator is used to generate N mutually orthogonal pseudo-random sequences required for phase code division multiple access encoding;

[0075] The phase modulator group is used to perform phase modulation on each signal beam output by the polarizer group using a pseudo-random sequence generated by the signal generator to form N signal beams carrying phase address codes;

[0076] The transmitting end objective lens group is used to focus the N signal light beams carrying the phase address code output by the phase modulator group respectively, so that the N signal light beams are focused to the corresponding positions on the sample respectively; and reflect the N SHG signal light beams.

[0077] By irradiating the sample with N signal light beams at the same time, parallel detection of the sample is achieved, and N points of the sample can be detected at one time, which improves the detection efficiency. The address encoding of the light beam is achieved through phase code division multiple access coding, which can be used to distinguish each light beam later and distinguish the SHG of the sample detection point carried by the light beam.

[0078] Specifically, the output optical path assembly includes a receiving end objective lens group, an analyzer group, a filter, a receiving end coupling lens group and a signal collector; wherein,

[0079] The receiving end objective lens group is used to collimate the N SHG signal light beams reflected by the sample respectively;

[0080] The polarizer group is used to select the polarization states of the N light beams output by the receiving end objective lens group respectively, and output the light beams whose polarization angles meet the test requirements;

[0081] The filter is used to filter the N light beams output by the analyzer group to remove the fundamental frequency light;

[0082] The receiving end coupling lens group is used to focus the N light beams output by the filter to the receiving position of the signal collector respectively;

[0083] The signal collector is used to perform coherent detection on the signal light beam and the reference light beam entering the receiving position and output the electrical signal.

[0084] Specifically, the reference light path assembly includes: a reference light polarizer, a frequency doubling crystal, a reference light objective lens, a reference light analyzer, a reference light filter, an optical path controller, and a reference light coupling lens group;

[0085] The reference light polarizer is used to adjust the polarization state of the fundamental frequency light of a reference light beam output from the beam splitter so that the polarization angle of the reference light beam is the same as the polarization angle of the signal light beam;

[0086] The frequency doubling crystal is used to frequency-double the light beam output by the reference light polarizer to obtain a reference light beam for SHG;

[0087] Preferably, a frequency doubling crystal including a BBO crystal is used for frequency doubling;

[0088] The reference light objective lens is used to collimate the light beam output by the frequency doubling crystal;

[0089] The reference light analyzer is used to select the polarization state of the light beam output by the reference light objective lens, and output the light beam with the same polarization angle as the signal light beam;

[0090] The reference light filter is used to filter the light beam output by the reference light analyzer to remove the fundamental frequency light;

[0091] The optical path controller is used to control the optical path of the light beam output by the reference light filter so that the optical path of the reference light beam entering the signal collector is consistent with the optical path of the outgoing light beam;

[0092] The reference light coupling lens is used to focus the light beam output by the optical path controller, and focuses the light beam output by the optical path controller to the receiving position of the signal collector for subsequent coherent detection.

[0093] Preferably, in order to achieve faster and more accurate optical path control and to meet the optical path alignment requirements, the reference optical path assembly further includes: a first optical path adjustment assembly and a second optical path adjustment assembly;

[0094] The first optical path adjustment component is used to adjust the optical path of a reference light beam output by the beam splitter to align with the reference light polarizer, so as to adjust the polarization state of the reference light beam;

[0095] The second optical path adjustment component is used to adjust the optical path of the light beam output by the reference light filter to align with the optical path controller to perform optical path control of the reference light beam.

[0096] The second harmonic characterization system also includes a processing control unit, which is connected to the signal collector; it is used to perform power amplification, signal splitting, phase locking, and N-channel phase address code demodulation on the signal output by the signal collector after coherent detection, and then detect N-channel SHG carrying sample defect information.

[0097] Specifically, the processing control unit includes: a power division amplifier, a phase address code demodulator and a digital control terminal;

[0098] The power divider amplifier is used to amplify the power of the signal and divide the signal into N channels; the output power amplified signals are:

[0099] The phase address code demodulator is used to perform address code demodulation on the N-channel signals after power amplification respectively using the same N-channel code division multiple access pseudo-random sequence as that in the incident light path component, so as to obtain N-channel demodulated signals corresponding to the positions where the N signal light beams irradiate the samples;

[0100] The digital control terminal is used to perform frequency discrimination on N demodulated signals respectively to obtain N SHGs carrying sample defect information.

[0101] Preferably, a phase-locked circuit is further connected between the power divider amplifier and the phase address code demodulator in the processing control unit; the processing control unit and the incident light path component share a signal generator;

[0102] The phase-locked circuit is used to phase-lock N channels of signals respectively; the phase deviation of each locked channel of signal is input into the signal generator, and the phase of each channel of code division multiple access pseudo-random sequence output by the signal generator is adjusted so that the phase deviation of the collected signal and the incident end is 0, that is, the starting time of each optical path is the same to ensure coherence; after address code demodulation of each channel of signal output by the phase-locked circuit and each channel of code division multiple access pseudo-random sequence with phase adjusted generated by the signal generator, N channels of demodulated signals corresponding to the positions of the samples irradiated by the N signal light beams are obtained.

[0103] Preferably, in order to ensure the best coherence state, the numerical control terminal also converts one of the N demodulated signals into a corresponding control voltage after real-time signal amplitude acquisition by a high-precision ADC. The control voltage is amplified by a high-voltage amplifier and output to an optical path controller; the optical path controller is a piezoelectric optical path controller; the piezoelectric ceramics in the optical path controller are deformed under high-voltage drive, pushing the reflector in the optical path controller to move, thereby adjusting the optical path of the reference beam, adjusting the coherence state of the signal beam and the reference beam, and thus achieving the best coherence state;

[0104] The adjustment steps of the optical path of the reference beam are as follows:

[0105] 1) Get the current signal amplitude value and control voltage value;

[0106] 2) Apply a small voltage disturbance δV;

[0107] 3) Compare the signal amplitude before and after the disturbance;

[0108] 4) If the amplitude increases, maintain the disturbance direction;

[0109] 5) If the amplitude decreases, change the disturbance direction;

[0110] 6) Iterate until the maximum value is reached.

[0111] In the preferred embodiment, it also includes an arc guide rail, an incident arm and an exit arm;

[0112] The arc guide is located directly above the sample stage; the incident arm and the exit arm are slidably assembled on the arc guide, and both can slide on the arc guide around the sample stage;

[0113] The incident arm is the supporting structure of the incident light path component, and the output arm is the supporting structure of the output light path component. By controlling the positions of the incident arm and the output arm on the arc guide rail, the incident angle of the signal light beam incident on the sample is determined, and the output light path component is located in the reflected light beam of the sample, thereby realizing sample detection at the set incident angle.

[0114] In a preferred solution, the reference optical path component is located in a space surrounded by the arc guide rail, the incident arm and the exit arm, the first optical path adjustment component includes a first reflector, and the second optical path adjustment component includes a second reflector and a third reflector;

[0115] A reference light beam outputted by the beam splitter in the incident light path component is incident on the first reflector, and the reference light beam reflected by the first reflector is aligned with the reference light polarizer and is incident on the reference light polarizer;

[0116] The second reflector and the third reflector are arranged opposite to each other, the reference light beam output by the reference light filter is incident on the second reflector, the reference light beam reflected by the second reflector is incident on the third reflector, and the reference light beam reflected by the third reflector is aligned with the optical path controller and is incident on the optical path controller.

[0117] In a preferred embodiment, the sample stage is provided with a motion module, so that the sample (tested material) can be moved in space so that the laser can characterize the entire area of ​​the sample.

[0118] The motion module includes an XY plane motion module and a rotation module around the Z axis. The XY motion module is used to adjust the position of the material to be tested so that the second harmonic multi-threaded detection system can complete step scanning during operation; while the rotation module around the Z axis rotates the material to be tested around the detection center point, which is used to adjust the azimuth angle during the detection process and obtain the dependence of the SHG of the material to be tested on the azimuth angle. After the light beam is injected into the material to be tested, due to the nonlinear effect of the material, the emitted second harmonic will carry the defect information of the sample.

[0119] Specifically, the optical path and signal flow of the second harmonic characterization system based on phase code division multiple access are as follows: Figure 2 shown.

[0120] In summary, compared with the existing second harmonic characterization system, the second harmonic characterization system based on phase code division multiple access disclosed in this embodiment can simultaneously perform second harmonic characterization of multiple points of the material to be tested, effectively improving the characterization efficiency of the second harmonic characterization system.

[0121] In addition, in the multi-threaded second harmonic characterization system, the sample stage carrying the material to be tested is equipped with a motion module, which can make the sample stage and the material to be tested carried by it move in multiple dimensions, including movement in the x, y, and z directions and 360-degree rotation with the normal direction of the xy plane as the axis, thereby changing the azimuth angle of the incident light. The arc guide rail above the sample stage can control the incident angle of the fundamental frequency light, and the polarizer group of the incident arm adjusts the polarization angle of the fundamental frequency light to provide the polarization angle required for the test.

[0122] In summary, the various devices in the multi-threaded second harmonic characterization system cooperate with each other to realize the detection of azimuth angle, incident angle and polarization angle dependence in second harmonic characterization.

[0123] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A second harmonic characterization system based on phase code division multiple access, characterized in that: include: Incident light path component, exit light path component, reference light path component, sample and sample stage; The incident light path component is used to polarize and phase code division multiple access modulate the N signal light beams after the main laser pulse is split in the incident light path, so as to obtain N signal light beams carrying phase address codes, which are respectively focused and irradiated on the sample on the sample stage, and reflect N SHG signal light beams; An outgoing optical path component is used to receive N SHG signal light beams, and obtain N SHG detection light beams after collimation, polarization analysis, filtering and focusing respectively; A reference optical path component is used to polarize, frequency-double, analyze, filter, control the optical path and focus a reference beam after the main laser pulse is split to form a reference beam for SHG; After coupling and coherent detection of N SHG-carrying detection beams and SHG reference beams, signal splitting and N-channel phase address code demodulation are performed, and N-channel SHG signals carrying sample defect information are detected.

2. The second harmonic characterization system based on phase code division multiple access according to claim 1, characterized in that: The incident light path assembly includes: a laser, a beam splitter, a polarizer group, a phase modulator group, a signal generator and a transmitting end objective lens group; wherein, The laser is used to generate a main laser pulse; The beam splitter is used for laser multi-path beam splitting to split the main laser pulse into N signal beams and 1 reference beam; The polarizer group is used to adjust the polarization state of the fundamental frequency light of the N signal light beams to obtain a polarization angle that meets the test requirements; The signal generator is used to generate N mutually orthogonal pseudo-random sequences required for phase code division multiple access encoding; The phase modulator group is used to perform phase modulation on each signal beam output by the polarizer group using a pseudo-random sequence generated by the signal generator to form N signal beams carrying phase address codes; The transmitting end objective lens group is used to focus the N signal light beams carrying the phase address code output by the phase modulator group respectively, so that the N signal light beams are focused to the corresponding positions on the sample respectively; and reflect the N SHG signal light beams.

3. The second harmonic characterization system based on phase code division multiple access according to claim 2, characterized in that: The output optical path assembly includes a receiving end objective lens group, an analyzer group, a filter, a receiving end coupling lens group and a signal collector; wherein, The receiving end objective lens group is used to collimate the N SHG signal light beams reflected by the sample respectively; The polarizer group is used to select the polarization states of the N light beams output by the receiving end objective lens group respectively, so as to output the light beams whose polarization angles meet the test requirements; The filter is used to filter the N light beams output by the analyzer group to remove the fundamental frequency light; The receiving end coupling lens group is used to focus the N light beams output by the filter to the receiving position of the signal collector respectively; The signal collector is used to perform coherent detection on the signal light beam and the reference light beam entering the receiving position and output an electrical signal.

4. The second harmonic characterization system based on phase code division multiple access according to claim 3 is characterized in that: The reference light path assembly includes: a reference light polarizer, a frequency doubling crystal, a reference light objective lens, a reference light analyzer, a reference light filter, an optical path controller, and a reference light coupling lens group; The reference light polarizer is used to adjust the polarization state of the fundamental frequency light of a reference light beam output from the beam splitter so that the polarization angle of the reference light beam is the same as the polarization angle of the signal light beam; The frequency doubling crystal is used to frequency-double the light beam output by the reference light polarizer to obtain a frequency-doubled reference light beam; The reference light objective lens is used to collimate the light beam output by the frequency doubling crystal; The reference light analyzer is used to select the polarization state of the light beam output by the reference light objective lens, and output the light beam with the same polarization angle as the signal light beam; The reference light filter is used to filter the light beam output by the reference light analyzer to remove the fundamental frequency light; The optical path controller is used to control the optical path of the light beam output by the reference light filter so that the optical path of the reference light beam entering the signal collector is consistent with the optical path of the outgoing light beam; The reference light coupling lens is used to focus the light beam output by the optical path controller, and focuses the light beam output by the optical path controller to the receiving position of the signal collector for subsequent coherent detection.

5. The second harmonic characterization system based on phase code division multiple access according to claim 4, characterized in that: The reference optical path component also includes: a first optical path adjustment component and a second optical path adjustment component; The first optical path adjustment component is used to adjust the optical path of a reference light beam output by the beam splitter to align with the reference light polarizer, so as to adjust the polarization state of the reference light beam; The second optical path adjustment component is used to adjust the optical path of the light beam output by the reference light filter to align with the optical path controller to perform optical path control of the reference light beam.

6. The second harmonic characterization system based on phase code division multiple access according to claim 4, characterized in that: The second harmonic characterization system also includes a processing control unit, which is connected to the signal collector; used to perform power amplification, signal beam splitting, phase locking, and N-channel phase address code demodulation on the signal output by the signal collector after coherent detection, and then detect the second harmonic signal characterization of N channels carrying sample defect information; The processing control unit includes: a power division amplifier, a phase address code demodulator and a digital control terminal; The power splitter amplifier is used to amplify the power of the signal and split the signal; outputting N channels of power-amplified signals; The phase address code demodulator is used to perform address code demodulation on the N-channel signals after power amplification respectively using the same N-channel code division multiple access pseudo-random sequence as that in the incident light path component, so as to obtain N-channel demodulated signals corresponding to the positions where the N signal light beams irradiate the samples; The numerical control terminal is used to analyze the N demodulated sample-carrying defect signals and complete SHG characterization.

7. The second harmonic characterization system based on phase code division multiple access according to claim 6, characterized in that: A phase-locked circuit is also connected between the power divider amplifier and the phase address code demodulator in the processing control unit; the processing control unit and the incident light path component share a signal generator; The phase-locked circuit is used to phase-lock N signals respectively; the starting phase deviations of the locked detection signals and the reference signals are input into the signal generator, and the phases of the code division multiple access pseudo-random sequences output by the signal generator are adjusted so that the phase deviations of the collected signals and the incident end are 0, that is, the starting times of the various optical paths are the same to ensure coherence; after address code demodulation of the signals output by the phase-locked circuit and the code division multiple access pseudo-random sequences generated by the signal generator with the phases adjusted, N demodulated signals corresponding to the positions of the samples irradiated by the N signal light beams are obtained.

8. The second harmonic characterization system based on phase code division multiple access according to claim 6, characterized in that: The numerical control terminal also converts one of the N demodulated signals into a corresponding control voltage after real-time signal amplitude acquisition by a high-precision ADC; the control voltage is amplified by a high-voltage amplifier and output to an optical path controller; the optical path controller is a piezoelectric optical path controller; the piezoelectric ceramics in the optical path controller are deformed under high-voltage drive, pushing the reflector in the optical path controller to move, thereby adjusting the optical path of the reference beam, adjusting the coherence state of the signal beam and the reference beam, and achieving the best coherence state; The adjustment steps of the optical path of the reference beam are as follows: 1) Get the current signal amplitude value and control voltage value; 2) Apply a small voltage disturbance; 3) Compare the signal amplitude before and after the disturbance; 4) If the amplitude increases, maintain the disturbance direction; 5) If the amplitude decreases, change the disturbance direction; 6) Iterate until the maximum value is reached.

9. The second harmonic characterization system based on phase code division multiple access according to any one of claims 1 to 8, characterized in that: It also includes: an arc guide rail, an incident arm and an exit arm; The arc guide is located directly above the sample stage; the incident arm and the exit arm are slidably assembled on the arc guide, and both can slide on the arc guide around the sample stage; The incident arm is the supporting structure of the incident light path component, and the output arm is the supporting structure of the output light path component. By controlling the positions of the incident arm and the output arm on the arc guide rail, the incident angle of the signal light beam incident on the sample is determined, and the output light path component is located in the reflected light beam of the sample, thereby realizing sample detection at the set incident angle.

10. The second harmonic characterization system based on phase code division multiple access according to claim 9, characterized in that: The sample stage is provided with a motion module to move the position of the sample in space, so that the laser can characterize the entire area of ​​the sample; The motion module includes: an XY plane motion module and a rotation module around the Z axis; the XY motion module is used to adjust the position of the material under test so that the second harmonic multi-threaded detection system can complete step scanning during operation; the rotation module around the Z axis allows the material under test to rotate around the detection center point, which is used to adjust the azimuth angle during the detection process and obtain the dependence of the SHG of the material under test on the azimuth angle.

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