Second harmonic characterization system based on coherent detection technology

Abstract

The invention relates to a second harmonic characterization system based on a coherent detection technology. The incident light path assembly is used for carrying out wavelength and power control, polarization direction adjustment and filtering on the laser pulse and then dividing the laser pulse into two light beams, one light beam is irradiated on a sample after being subjected to optical axis adjustment and focusing in an incident light path, and the light beam is modulated by the sample to generate an SHG carrying defect information; the other beam enters a coherent detection light path; the coherent detection light path assembly is used for performing frequency multiplication, filtering, polarization direction and intensity adjustment, optical path compensation and phase shift on a light beam entering a coherent detection light path to form a reference light beam with an introduced optical path and phase disturbance; the emergent light path assembly is used for performing collimation optical axis adjustment on the signal light beam reflected by the sample and then combining the signal light beam with the reference light beam; the combined light beam realizes coherence on a detector, and a specific phase matching state is determined after phase scanning to extract an interface signal. According to the method, the interface signal extraction of the non-centrosymmetric material system is realized, and the use scene of the SHG representation technology is expanded.

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 coherent detection technology. Background Art

[0002] In the field of modern optics and optoelectronics, second harmonic generation (SHG) technology has become an important nonlinear optical phenomenon and is widely used in fields such as material analysis, bioimaging and optical communications. Second harmonic generation refers to the process in which a new light wave with a frequency twice that of the original light is generated when a light wave passes through a nonlinear medium. This process not only depends on the nonlinear properties of the medium, but is also affected by factors such as wavelength, light intensity and phase matching, making SHG technology a powerful tool for detecting material properties and internal structures. For example, SHG technology can be used to locate and identify structural defects such as stacking faults and dislocations in wafers, and 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] When SHG technology is applied in the field of wafer characterization, the bulk signal of non-centrosymmetric material systems is strong, so that the interface signal carrying defect information is submerged in the strong bulk signal, affecting the accurate measurement of defect information. Therefore, the existing SHG technology is not applicable to non-centrosymmetric material systems with strong bulk signals, which greatly restricts the development and application of this technology. Summary of the invention

[0004] In view of the above analysis, the present invention aims to disclose a second harmonic characterization system based on coherent detection technology, which utilizes coherent detection technology to extract interface signals through the difference in phase between second harmonic interface signals and body signals.

[0005] The invention discloses a second harmonic characterization system based on coherent detection technology, comprising: an incident light path component, an output light path component, a coherent detection light path component, a sample and a sample stage;

[0006] The incident light path component is used to perform wavelength control, power control, polarization direction adjustment and filtering on the main laser pulse, and then split it into two beams of light. One beam is used as a signal beam in the incident light path, and then the optical axis is adjusted and focused to irradiate the sample on the sample stage. The beam is modulated by the sample to generate SHG carrying defect information; the other beam enters the coherent detection light path;

[0007] The coherent detection optical path component is used to perform frequency doubling, filtering, polarization direction and intensity adjustment, optical path compensation and phase shifting on the light beam entering the coherent detection optical path, thereby forming a reference light beam that introduces optical path and phase disturbance;

[0008] The output optical path component is used to collimate the signal light beam reflected by the sample, adjust the optical axis, and then combine it with the reference light beam; after the combined light beam is polarized and filtered, it is coherent on the detector and photoelectric detection is performed;

[0009] When the reference beam with introduced optical path and phase perturbations is consistent with the polarization direction, optical path and phase of the beam reflected from the sample interface, beam coherence occurs, and the SHG characterization of the interface signal is detected by photoelectric detection.

[0010] Furthermore, the sample belongs to a non-centrosymmetric material system including silicon carbide, gallium nitride and diamond.

[0011] Further, the incident light path component includes: a laser, a first half-wave plate, a first polarizer, a first filter, a beam splitter, a first beam adjuster and a focusing mirror;

[0012] The laser is used to generate an ultrashort laser pulse with incident linear polarization and output it to the first half-wave plate;

[0013] The first half-wave plate is used to change the polarization direction of the incident laser beam according to test requirements;

[0014] The first polarizer is used to enhance the extinction ratio of the light beam output by the first half-wave plate, thereby enhancing the polarization characteristics of the polarized light;

[0015] The first filter is used to filter the light beam output by the first polarizer to remove stray light other than the laser wavelength output by the laser;

[0016] The beam splitter is used to split the light beam output by the first filter into two beams, one of which enters the first beam adjuster as a signal beam, and the other enters the coherent detection optical path;

[0017] The first beam adjuster is used to further adjust the optical axis of the incoming signal beam to obtain a signal beam that meets the test conditions;

[0018] The focusing mirror is used to focus the light beam output by the first light beam adjuster onto the sample on the sample stage to generate second harmonic.

[0019] Furthermore, the incident light path component also includes: a beam splitter and a light spot profile analyzer;

[0020] The beam splitter is located between the focusing mirror and the sample, and is used to split a portion of the signal light beam focused on the sample to the light spot profile analyzer;

[0021] The light spot profile analyzer is used to analyze the focal spot intensity distribution of the light beam received from the beam splitter and monitor the profile of the signal light beam incident on the sample.

[0022] Further, a microscope and a height meter are arranged directly above the sample;

[0023] The position where the light beam is irradiated is observed by a microscope placed just above the sample; the height of the sample is measured by a height meter placed just above the sample.

[0024] Furthermore, the coherent detection optical path component includes: a frequency doubling crystal, a second filter, a second half-wave plate, an attenuation plate, an optical path compensation device and a phase shifter;

[0025] The frequency doubling crystal is used to frequency-double the split light entering the coherent detection optical path to generate a reference light beam carrying the second harmonic;

[0026] The second filter is used to filter out the fundamental frequency light of the light beam output by the frequency doubling crystal;

[0027] The second half-wave plate is used to adjust the polarization direction of the light beam output by the second filter to be the same as the polarization direction of the signal light beam;

[0028] The attenuation plate is used to control the intensity of the output light beam to match the intensity of the signal light and achieve coherence;

[0029] The optical path compensation device is used to perform optical path compensation on the light beam output by the second half-wave plate;

[0030] The phase shifter is used to change the phase of the light beam output by the optical path compensation device;

[0031] After frequency doubling, filtering, polarization direction and intensity adjustment by the coherent detection optical path component, and then optical path compensation and phase shifting, a reference beam is obtained, which has the same frequency, amplitude, and polarization direction as the signal beam and introduces optical path and phase disturbances; the reference beam enters the output optical path component and is combined with the signal beam reflected by the sample.

[0032] Furthermore, the output optical path assembly includes: a collimator, an objective lens adjustment frame, a second beam adjuster, a beam combiner, a second polarizer, a second filter and a detection device;

[0033] The collimator is used to collimate the signal light beam reflected by the sample; the SHG signal light beam reflected by the sample carries defect information;

[0034] The objective lens adjustment frame is used to adjust the position of the collimating lens;

[0035] The second beam adjuster is used to further adjust the optical axis of the light beam output by the collimator;

[0036] The beam combiner is used to combine the signal beam output from the second beam adjuster with the reference beam entering the beam combiner, and then output the combined beam;

[0037] The second polarizer is used to screen the components of the combined light beam with adjustable polarization direction, and ensure that the vibration direction of the light beam on the detector is consistent, thereby optimizing the coherence effect;

[0038] The second filter is a short-pass filter, which is used to perform short-pass filtering on the combined light beam output by the second polarizer, transmit short wavelengths, and reflect long wavelengths; reflect the fundamental frequency light, and output the combined second harmonic light beam to the detection device;

[0039] The detection device is a photoelectric detection device, which is used to perform photoelectric detection on the incoming combined second harmonic light beam.

[0040] Furthermore, it also includes: an arc guide rail, an incident arm, an exit arm; a first tangential stepping motor and a second tangential stepping motor;

[0041] 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 center point of the sample stage;

[0042] 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, so as to realize sample detection at the set incident angle;

[0043] The first tangential stepping motor is connected to the incident arm to drive the incident arm to slide in the direction of the vertical arc guide rail to change the focal position of the incident light path;

[0044] The second tangential stepping motor is connected to the output arm, and drives the output arm to slide in the direction of the vertical arc guide rail, so as to change the position of the collimating mirror in the output light path and ensure the collimation state of the light beam in the output light path.

[0045] 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;

[0046] The motion module includes: an XY plane motion module, a Z axis compensation 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; the Z axis compensation module is used to compensate for the system deviation caused by different sample thicknesses, and 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.

[0047] Furthermore, it also includes: a control unit;

[0048] The control unit is used to control controllable mechanical devices including an arc guide rail, a first tangential stepping motor and a second tangential stepping motor, a first beam adjuster and a second beam adjuster, a sample stage, a height meter, and an objective lens adjustment frame, and adjusts the optical path state according to parameter requirements including the incident angle and sample thickness required for the test to ensure the SHG signal intensity.

[0049] The present invention can achieve one of the following beneficial effects:

[0050] Compared with the existing second harmonic characterization system, this system introduces coherent detection technology to realize the extraction of bulk and interface signals in non-centrosymmetric material systems, further expanding the application scenarios of second harmonic characterization technology;

[0051] In addition, through controllable mechanical devices, the optical path system can adjust the optical path state when parameters such as the incident angle and sample thickness change, thereby ensuring signal strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] 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;

[0053] Figure 1 A schematic diagram of the connection components of a second harmonic characterization system based on coherent detection technology in an embodiment of the present invention;

[0054] Figure numerals: 1. arc guide rail, 2. first tangential stepper motor, 3. laser, 4. first half-wave plate, 5. first polarizer, 6. first filter, 7. beam splitter, 8. frequency doubling crystal, 9. second filter, 10. second half-wave plate, 11 attenuation plate, 12. optical path compensation device, 13. phase shifter, 14. reflector, 15. first beam adjuster, 16. focusing mirror, 17. beam splitter, 18. spot profile analyzer, 19. altimeter, 20. microscope, 21. sample stage, 22. sample / wafer, 23. collimator, 24. objective lens adjustment stand, 25. second beam adjuster, 26. beam combiner, 27. second polarizer, 28. second filter, 29. spectrometer / single photon counter, 30. second tangential stepper motor. DETAILED DESCRIPTION

[0055] 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.

[0056] One embodiment of the present invention discloses a second harmonic characterization system based on coherent detection technology, such as Figure 1 As shown, including:

[0057] Incident light path component, exit light path component, coherent detection light path component, sample and sample stage;

[0058] The incident light path component is used to perform wavelength control, power control, polarization direction adjustment and filtering on the main laser pulse, and then split it into two beams of light. One beam is used as a signal beam in the incident light path, and then the optical axis is adjusted and focused to irradiate the sample on the sample stage. The beam is modulated by the sample to generate SHG carrying defect information; the other beam enters the coherent detection light path;

[0059] The coherent detection optical path component is used to perform frequency doubling, filtering, polarization direction and intensity adjustment, optical path compensation and phase shifting on the light beam entering the coherent detection optical path, thereby forming a reference light beam that introduces optical path and phase disturbance;

[0060] The output optical path component is used to collimate the signal light beam reflected by the sample, adjust the optical axis, and then combine it with the reference light beam; after the combined light beam is polarized and filtered, it is coherent on the detector and photoelectric detection is performed;

[0061] When the reference beam with introduced optical path and phase perturbations is consistent with the polarization direction, optical path and phase of the beam reflected from the sample interface, beam coherence occurs, and the SHG characterization of the interface signal is detected by photoelectric detection.

[0062] Specifically, the sample belongs to a non-centrosymmetric material system including silicon carbide, gallium nitride and diamond.

[0063] Specifically, the incident light path component includes: a laser, a first half-wave plate, a first polarizer, a first filter, a beam splitter, a first beam adjuster and a focusing mirror;

[0064] The laser is used to generate an ultrashort laser pulse with incident linear polarization and output it to the first half-wave plate;

[0065] Preferably, the parameters of the linearly polarized ultrashort laser pulse are: wavelength 800 nm; pulse width 100 fs.

[0066] The first half-wave plate is used to change the polarization direction of the incident laser beam according to test requirements;

[0067] The first polarizer is used to enhance the extinction ratio of the light beam output by the first half-wave plate, thereby enhancing the polarization characteristics of the polarized light;

[0068] The first filter is used to filter the light beam output by the first polarizer to remove stray light other than the laser wavelength output by the laser;

[0069] The beam splitter is used to split the light beam output by the first filter into two beams, one of which enters the first beam adjuster as a signal beam, and the other enters the coherent detection optical path;

[0070] The first beam adjuster is used to further adjust the optical axis of the incoming signal beam to obtain a signal beam that meets the test conditions;

[0071] The focusing mirror is used to focus the light beam output by the first light beam adjuster onto the sample on the sample stage to generate second harmonic.

[0072] Preferably, the incident light path component further comprises: a beam splitter and a light spot profile analyzer;

[0073] The beam splitter is located between the focusing mirror and the sample, and is used to split a portion of the signal light beam focused on the sample to the light spot profile analyzer;

[0074] The light spot profile analyzer is used to analyze the focal spot intensity distribution of the light beam received from the beam splitter and monitor the profile of the signal light beam incident on the sample;

[0075] By monitoring the shape of the signal light beam, it is determined whether it is a Gaussian distribution; in a preferred solution, a spatial light modulator can be added in front of the spot shape analyzer to shape the light beam into a special light beam, such as a flat-top beam.

[0076] In a more preferred embodiment, a microscope and a height meter are arranged directly above the sample;

[0077] The position where the light beam is irradiated is observed by a microscope placed just above the sample; the height of the sample is measured by a height meter placed just above the sample.

[0078] Specifically, the coherent detection optical path component includes: the coherent detection optical path component includes: a frequency doubling crystal, a second filter, a second half-wave plate, an attenuation plate, an optical path compensation device and a phase shifter;

[0079] The frequency doubling crystal is used to frequency-double the split light entering the coherent detection optical path to generate a reference light beam carrying the second harmonic;

[0080] The second filter is used to filter out the fundamental frequency light of the light beam output by the frequency doubling crystal;

[0081] The second half-wave plate is used to adjust the polarization direction of the light beam output by the second filter to be the same as the polarization direction of the signal light beam;

[0082] The attenuation plate is used to control the intensity of the output light beam to match the intensity of the signal light and achieve coherence;

[0083] The optical path compensation device is used to perform optical path compensation on the light beam output by the second half-wave plate;

[0084] The phase shifter is used to change the phase of the light beam output by the optical path compensation device;

[0085] After frequency doubling, filtering, polarization direction and intensity adjustment by the coherent detection optical path component, and then optical path compensation and phase shifting, a reference beam is obtained, which has the same frequency, amplitude, and polarization direction as the signal beam and introduces optical path and phase disturbances; the reference beam enters the output optical path component and is combined with the signal beam reflected by the sample.

[0086] Optical path and phase disturbances are introduced into the reference beam to search for a reference beam that is coherent with the interface signal or bulk signal carrying SHG reflected by the sample.

[0087] In order to enable the reference beam to be aligned with and enter the device for beam combining in the output optical path assembly, the coherent detection optical path assembly also includes an optical path adjustment device; for example, a plane mirror or other device that can change the optical path, so that the reference beam can enter the beam combining device in the output optical path assembly. The optical path adjustment device should be used in conjunction with an optical path compensation device to ensure that the optical path of the reference beam matches the optical path of the signal beam from beam splitting to beam combining.

[0088] Specifically, the output optical path assembly includes: a collimator, an objective lens adjustment frame, a second beam adjuster, a beam combiner, a second polarizer, a second filter and a detection device;

[0089] The collimator is used to collimate the signal light beam reflected by the sample; the SHG signal light beam reflected by the sample carries defect information;

[0090] The objective lens adjustment frame is used to adjust the position of the collimating lens;

[0091] The second beam adjuster is used to further adjust the optical axis of the light beam output by the collimator;

[0092] The beam combiner is used to combine the signal beam output from the second beam adjuster with the reference beam entering the beam combiner, and then output the combined beam;

[0093] The second polarizer is used to screen the components of the combined light beam with adjustable polarization direction, and ensure that the vibration direction of the light beam on the detector is consistent, thereby optimizing the coherence effect;

[0094] The second filter is a short-pass filter, which is used to perform short-pass filtering on the combined light beam output by the second polarizer, transmit short wavelengths, and reflect long wavelengths; reflect the fundamental frequency light, and output the combined second harmonic light beam to the detection device;

[0095] The detection device is a photoelectric detection device, which is used to perform photoelectric detection on the incoming combined second harmonic light beam.

[0096] Preferably, the photoelectric detection device is a spectrometer / single photon counter.

[0097] Preferably, the output optical path assembly further comprises an objective lens adjustment frame of a collimating lens, which is used to adjust the position of the collimating lens; the position of the collimating lens is adjusted according to the incident angle of the signal light beam and the change of parameters including the sample thickness to meet the collimation of the sample reflected light beam.

[0098] When detecting samples of non-centrosymmetric material systems, the reflected light beam carries both the interface signal and the bulk signal of SHG; and since the positions of the interface signal and the bulk signal reflected by the sample are different, there are differences in the optical path and the phase. In the implementation of the second harmonic characterization system based on the coherent detection technology of this embodiment, by adjusting the optical path compensation device and the phase shifter of the coherent detection optical path component, matching optical path scanning and matching phase scanning are performed, then coherence with the interface signal carrying SHG and coherence with the bulk signal carrying SHG will occur in the combined light in the combiner. After the coherence result is detected by the detection device, the detection result under the corresponding coherence is obtained. By analyzing the two coherent detection results, the coherence with the interface signal carrying SHG and the coherence with the bulk signal carrying SHG are distinguished according to the difference in optical path length and the difference in detection waveform, and the optical path compensation value of the optical path compensation device and the phase shift value of the phase shifter in the two cases are used.

[0099] The optical path compensation value of the optical path compensation device and the phase shift value of the phase shifter are set to values ​​that are coherent with the interface signal carrying SHG, thereby achieving SHG extraction of the sample interface signal.

[0100] Likewise, if it is necessary to extract the SHG of the bulk signal, the optical path compensation value of the optical path compensation device and the phase shift value of the phase shifter can be set to values ​​that generate coherence with the bulk signal carrying SHG.

[0101] In a preferred embodiment, the arc guide rail, the incident arm, the exit arm; the first tangential stepping motor and the second tangential stepping motor;

[0102] 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 center point of the sample stage;

[0103] 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.

[0104] The coherent detection optical path component is located in a space surrounded by the arc guide rail, the incident arm and the output arm; the reference beam output by the phase shifter is reflected to the beam combiner of the output optical path component through a reflector;

[0105] The first tangential stepping motor is connected to the incident arm to drive the incident arm to slide in the direction of the vertical arc guide rail to change the focal position of the incident light path;

[0106] The second tangential stepping motor is connected to the output arm, and drives the output arm to slide in the direction of the vertical arc guide rail, so as to change the position of the collimating mirror in the output light path and ensure the collimation state of the light beam in the output light path.

[0107] In a preferred embodiment, the sample stage is provided with a motion module to move the sample (tested material) in space so that the laser can characterize the entire area of ​​the sample;

[0108] The motion module includes: an XY plane motion module, a Z axis compensation 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; the Z axis compensation module is used to compensate for the system deviation caused by different sample thicknesses, and 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.

[0109] After the light beam enters the material to be tested, the emitted second harmonic will carry the defect information of the sample due to the nonlinear effect of the material.

[0110] In a preferred embodiment, it also includes a control unit;

[0111] The control unit is used to control controllable mechanical devices including an arc guide rail, a first tangential stepping motor and a second tangential stepping motor, a first beam adjuster and a second beam adjuster, a sample stage, a height meter, and an objective lens adjustment frame, and adjusts the optical path state according to parameter requirements including the incident angle and sample thickness required for the test to ensure the SHG signal intensity.

[0112] For example, when replacing samples of different thicknesses, the height of the sample stage is adjusted based on the height information fed back by the altimeter to maintain the optimal measurement height of the system.

[0113] In summary, compared with the existing second harmonic characterization system, the second harmonic characterization system based on coherent detection technology disclosed in this embodiment introduces coherent detection technology to realize the extraction of bulk signals and interface signals in non-centrosymmetric material systems, further expanding the application scenarios of second harmonic characterization technology;

[0114] In addition, through controllable mechanical devices, the optical path system can adjust the optical path state when parameters such as the incident angle and sample thickness change, thereby ensuring signal strength.

[0115] 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 coherent detection technology, characterized in that: include: Incident light path component, exit light path component, coherent detection light path component, sample and sample stage; The incident light path component is used to perform wavelength control, power control, polarization direction adjustment and filtering on the main laser pulse, and then split it into two beams of light. One beam is used as a signal beam in the incident light path, and then the optical axis is adjusted and focused to irradiate the sample on the sample stage. The beam is modulated by the sample to generate SHG carrying defect information; the other beam enters the coherent detection light path; The coherent detection optical path component is used to perform frequency doubling, filtering, polarization direction and intensity adjustment, optical path compensation and phase shifting on the light beam entering the coherent detection optical path, thereby forming a reference light beam that introduces optical path and phase disturbance; The output optical path component is used to collimate the signal light beam reflected by the sample, adjust the optical axis, and then combine it with the reference light beam; after the combined light beam is polarized and filtered, it is coherent on the detector and photoelectric detection is performed; When the reference beam with introduced optical path and phase disturbance is consistent with the polarization direction, optical path and phase of the reflected beam from the sample interface, beam coherence occurs, and the SHG characterization of the interface signal is detected by photoelectric detection.

2. The second harmonic characterization system based on coherent detection technology according to claim 1, characterized in that: The samples belong to a non-centrosymmetric material system including silicon carbide, gallium nitride and diamond.

3. The second harmonic characterization system based on coherent detection technology according to claim 1, characterized in that: The incident light path assembly comprises: a laser, a first half-wave plate, a first polarizing plate, a first filter, a beam splitter, a first beam adjuster and a focusing mirror; The laser is used to generate an ultrashort laser pulse with incident linear polarization and output it to the first half-wave plate; The first half-wave plate is used to change the polarization direction of the incident laser beam according to test requirements; The first polarizer is used to enhance the extinction ratio of the light beam output by the first half-wave plate, thereby enhancing the polarization characteristics of the polarized light; The first filter is used to filter the light beam output by the first polarizer to remove stray light other than the laser wavelength output by the laser; The beam splitter is used to split the light beam output by the first filter into two beams, one of which enters the first beam adjuster as a signal beam, and the other enters the coherent detection optical path; The first beam adjuster is used to further adjust the optical axis of the incoming signal beam to obtain a signal beam that meets the test conditions; The focusing mirror is used to focus the light beam output by the first light beam adjuster onto the sample on the sample stage to generate second harmonic.

4. The second harmonic characterization system based on coherent detection technology according to claim 3, characterized in that: The incident light path components also include: a beam splitter and a light spot profile analyzer; The beam splitter is located between the focusing mirror and the sample, and is used to split a portion of the signal light beam focused on the sample to the light spot profile analyzer; The light spot profile analyzer is used to analyze the focal spot intensity distribution of the light beam received from the beam splitter and monitor the profile of the signal light beam incident on the sample.

5. The second harmonic characterization system based on coherent detection technology according to claim 4, characterized in that: Set up a microscope and a height meter directly above the sample; The position where the light beam is irradiated is observed by a microscope placed just above the sample; the height of the sample is measured by a height meter placed just above the sample.

6. The second harmonic characterization system based on coherent detection technology according to claim 3, characterized in that: The coherent detection optical path component comprises: a frequency doubling crystal, a second filter, a second half-wave plate, an attenuation plate, an optical path compensation device and a phase shifter; The frequency doubling crystal is used to frequency-double the split light entering the coherent detection optical path to generate a reference light beam carrying the second harmonic; The second filter is used to filter out the fundamental frequency light of the light beam output by the frequency doubling crystal; The second half-wave plate is used to adjust the polarization direction of the light beam output by the second filter to be the same as the polarization direction of the signal light beam; The attenuation plate is used to control the intensity of the output light beam to match the intensity of the signal light and achieve coherence; The optical path compensation device is used to perform optical path compensation on the light beam output by the second half-wave plate; The phase shifter is used to change the phase of the light beam output by the optical path compensation device; After frequency doubling, filtering, polarization direction and intensity adjustment by the coherent detection optical path component, and then optical path compensation and phase shifting, a reference beam is obtained, which has the same frequency, amplitude, and polarization direction as the signal beam and introduces optical path and phase disturbances; the reference beam enters the output optical path component and is combined with the signal beam reflected by the sample.

7. The second harmonic characterization system based on coherent detection technology according to claim 6, characterized in that: The output optical path assembly comprises: a collimator, an objective lens adjustment frame, a second beam adjuster, a beam combiner, a second polarizer, a second filter and a detection device; The collimator is used to collimate the signal light beam reflected by the sample; the SHG signal light beam reflected by the sample carries defect information; The objective lens adjustment frame is used to adjust the position of the collimating lens; The second beam adjuster is used to further adjust the optical axis of the light beam output by the collimator; The beam combiner is used to combine the signal beam output from the second beam adjuster with the reference beam entering the beam combiner, and then output the combined beam; The second polarizer is used to screen the components of the combined light beam with adjustable polarization direction, and ensure that the vibration direction of the light beam on the detector is consistent, thereby optimizing the coherence effect; The second filter is a short-pass filter, which is used to perform short-pass filtering on the combined light beam output by the second polarizer, transmit short wavelengths, and reflect long wavelengths; reflect the fundamental frequency light, and output the combined second harmonic light beam to the detection device; The detection device is a photoelectric detection device, which is used to perform photoelectric detection on the incoming combined second harmonic light beam.

8. The second harmonic characterization system based on coherent detection technology according to any one of claims 1 to 7, characterized in that: It also includes: an arc guide rail, an incident arm, an exit arm; a first tangential stepping motor and a second tangential stepping motor; 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 center point of 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, so as to realize sample detection at the set incident angle; The first tangential stepping motor is connected to the incident arm to drive the incident arm to slide in the direction of the vertical arc guide rail to change the focal position of the incident light path; The second tangential stepping motor is connected to the output arm, and drives the output arm to slide in the direction of the vertical arc guide rail, so as to change the position of the collimating mirror in the output light path and ensure the collimation state of the light beam in the output light path.

9. The second harmonic characterization system based on coherent detection technology according to claim 8, 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, a Z axis compensation 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; the Z axis compensation module is used to compensate for the system deviation caused by different sample thicknesses, and 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.

10. The second harmonic characterization system based on coherent detection technology according to claim 9, characterized in that: Also included: a control unit; The control unit is used to control controllable mechanical devices including an arc guide rail, a first tangential stepping motor and a second tangential stepping motor, a first beam adjuster and a second beam adjuster, a sample stage, a height meter, and an objective lens adjustment frame, and adjusts the optical path state according to parameter requirements including the incident angle and sample thickness required for the test to ensure the SHG signal intensity.

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