Multi-thread detection method and system for realizing second harmonic representation based on laser frequency modulation

Abstract

The invention relates to a multi-thread detection method and system for realizing second harmonic representation based on laser frequency modulation. The method comprises the following steps: splitting a main laser pulse in an incident light path, performing laser modulation to obtain N signal light beams carrying frequency codes, focusing, irradiating a sample, and forming an SHG signal light beam carrying defect information in an emergent light path; performing delay control and frequency multiplication on the reference light beam to form an SHG reference light beam; carrying out photoelectric detection and signal branching on the SHG signal light beam carrying defect information and the reference light beam to obtain N paths of frequency mixing signals; respectively carrying out de-spreading and phase locking on the N paths of frequency mixing signals to obtain frequency deviation values of all paths of signal light beams in the emergent light path; the frequency deviation value is converted into a frequency shift control quantity, and the frequency shift control quantity is fed back to an incident light path for frequency homodyne control of each signal light beam; and after homodyne control, resolving and outputting each path of mixing signal to obtain second harmonic representation of each signal light beam. According to the method, multi-thread detection is realized, and the second harmonic optical characterization performance is remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of nonlinear optical characterization, and in particular relates to a multi-threaded detection method and system for realizing second harmonic characterization based on laser frequency modulation. Background Art

[0002] In the field of modern optics and optoelectronics, second harmonic generation (SHG) technology has become an important nonlinear optical phenomenon, widely used in fields such as material analysis, bioimaging and optical communications. Second harmonic generation refers to the process of generating a new light wave with a frequency twice the original light frequency when a light wave passes through a nonlinear medium. This process not only depends on the nonlinear characteristics 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. In recent years, more and more studies have been conducted at home and abroad on the application of second harmonic technology to characterize the structural characteristics of materials. However, the current second harmonic characterization systems are mainly single-threaded, which limits the optical characterization efficiency of the second harmonic system and is not conducive to the promotion of this technology in industrial applications.

[0003] Multi-threaded detection can improve the efficiency of second harmonic system optical characterization, allowing the second harmonic characterization system to process multiple signals or perform multi-task operations at the same time, significantly improving the performance of second harmonic system optical characterization. It not only expands the application scope of nonlinear optics in multiple fields, but also provides new possibilities for efficient and rapid analysis of material properties, which is of great significance for scientific research and industrial applications. Summary of the invention

[0004] In view of the above analysis, the present invention aims to disclose a multi-threaded detection method and system for second harmonic characterization based on laser frequency modulation, so as to solve the problems of slow processing speed, limited processing capacity and insufficient sensitivity of single-threaded characterization of second harmonic.

[0005] The present invention discloses a multi-threaded detection method for realizing second harmonic characterization based on laser frequency modulation, comprising:

[0006] Step S1, performing laser spread spectrum modulation on the signal beam after the main laser pulse is split in the incident light path to obtain N signal beams carrying frequency codes, focusing and irradiating the sample on the sample stage, and forming an SHG signal beam carrying defect information in the outgoing light path;

[0007] Step S2, after the main laser pulse is split, a reference beam is delayed and frequency-multiplied to form an SHG reference beam that matches the optical path of the SHG signal beam carrying defect information;

[0008] Step S3, performing photoelectric detection and signal splitting on the SHG signal beam carrying defect information and the reference beam to obtain N mixed signals;

[0009] Step S4, respectively despreading and phase-locking the N mixed signals to obtain the frequency deviation value of each signal light beam in the outgoing light path; converting the frequency deviation value into a frequency shift control value, and feeding it back to the incident light path to perform frequency homodyne control of each signal light beam;

[0010] Step S5: After homodyne control, each mixing signal is resolved and output to obtain the second harmonic representation of each signal light beam.

[0011] Furthermore, step S1 includes:

[0012] 1) Splitting the main laser pulse into N signal beams and 1 reference beam through a beam splitter;

[0013] 2) Generate N mutually orthogonal pseudo-random code sequences through a signal generator; correspond each pseudo-random code sequence to a signal light beam, input them into a frequency shifter, and use the pseudo-random code sequence to frequency encode the signal light beam to obtain N signal light beams carrying frequency codes;

[0014] 3) N signal beams carrying frequency codes are amplified and focused to illuminate the sample on the sample stage; the sample reflects the signal beam, forming an SHG signal beam carrying defect information in the outgoing light path.

[0015] Furthermore, step S2 includes:

[0016] 1) A reference beam split from the beam splitter is delayed by a delay device to obtain a delayed reference beam;

[0017] 2) converting the delayed reference beam into a second harmonic by frequency doubling through a BBO crystal to obtain a SHG reference beam;

[0018] 3) Sending the SHG reference beam to the photodetector as a local oscillator beam to mix with the SHG signal beam carrying defect information in the outgoing optical path;

[0019] By setting the delay time of the delay device, the optical path lengths of the SHG signal beam carrying defect information and the local oscillator beam are made consistent.

[0020] Furthermore, components for changing the propagation direction of the optical path, including a plane mirror, are added between the beam splitter and the delay device, and between the BBO crystal and the photodetector, so that the reference beam split by the beam splitter enters the delay device, and the SHG reference beam output by the BBO crystal enters the photodetector.

[0021] Further, in step S3,

[0022] 1) Through the photodetector, the SHG signal beam carrying defect information in the outgoing light path as the signal light and the SHG reference beam as the local oscillator light are simultaneously received for coherent detection, and a mixed signal is output;

[0023] 2) After the output mixed signal is power amplified, a power divider is used to divide the mixed signal into N mixed signals; the signal power of each mixed signal is the same.

[0024] Further, in step S4,

[0025] 1) Despreading the N mixed signals by a despreader to obtain N despread signals;

[0026] Based on the orthogonality of the N pseudo-random code sequences in the incident light path, the same N pseudo-random code sequences as the incident light path are used in the despreader to despread the N mixed signals respectively to obtain N despread signals; each despread signal corresponds to a signal light beam, including the SHG signal carried by the signal light beam after irradiating the sample;

[0027] 2) After the N-channel despread signals are phase-locked by the phase-locked circuit, the frequency deviation value of each signal light beam in the outgoing light path is obtained;

[0028] 3) The frequency deviation value of each signal beam is converted into a frequency shift control value through A / D conversion, and fed back to the frequency shifter in the incident light path to control the frequency shift amount of each signal beam and perform zero-difference control on the frequency of each signal beam.

[0029] The present invention also discloses a multi-threaded high-efficiency characterization system for realizing second harmonic based on laser frequency modulation, comprising: an incident light path component, a reference light path component, a photoelectric detection and closed-loop control component and a characterization output component; wherein,

[0030] The incident light path component is used to perform laser spread spectrum modulation on the signal light beam after the main laser pulse is split in the incident light path to obtain N signal light beams carrying frequency codes, and then focus and irradiate the sample on the sample stage; thereby forming an SHG signal light beam carrying defect information in the outgoing light path;

[0031] A reference optical path component is used to delay and frequency-double a reference beam after the main laser pulse is split, so as to form an SHG reference beam that matches the optical path of the SHG signal beam carrying defect information;

[0032] The photoelectric detection and closed-loop control component is used to perform photoelectric detection and signal splitting on the SHG signal beam and the reference beam carrying defect information to obtain N-channel mixed signals; and respectively despread and phase-lock the N-channel mixed signals to obtain the frequency deviation value of each signal beam in the outgoing optical path; the frequency deviation value is converted into a frequency shift control amount, and fed back to the incident optical path to perform frequency homodyne control of each signal beam;

[0033] The characterization output component is used to output the second harmonic characterization obtained by solving each mixing signal after homodyne control.

[0034] Furthermore, the incident light path assembly includes: a laser, a beam splitter, a signal generator, a frequency shifter, a power amplifier group and a focusing lens; wherein,

[0035] The laser is used to generate a main laser pulse;

[0036] The beam splitter is used to split the main laser pulse into N signal beams and 1 reference beam;

[0037] The signal generator is used to generate N mutually orthogonal pseudo-random code sequences;

[0038] The frequency shifter comprises N frequency shift modules; each frequency shift module takes a pseudo-random code sequence and a signal beam as input, uses the input pseudo-random code sequence to frequency encode the input signal beam in the frequency shift module, and outputs a signal beam carrying the frequency code;

[0039] The power amplifier group includes N amplifiers, which are respectively connected to the N frequency shift modules to amplify the optical power of the signal light beams carrying the frequency code output by the frequency shift modules;

[0040] The focusing lens is used to focus the signal light beam carrying the frequency code after power amplification to irradiate the sample on the sample stage;

[0041] The sample reflects the signal beam, forming an SHG signal beam carrying defect information in the outgoing light path.

[0042] Further, the reference optical path component includes: a first optical path adjuster, a delay device, a BBO crystal and a second optical path modulator;

[0043] The first optical path adjuster is used to adjust the optical path between the beam splitter and the delay device so that the reference beam split by the beam splitter is input into the delay device;

[0044] The delay device is used to control the delay of the reference beam to obtain a delayed reference beam;

[0045] The BBO crystal is used to frequency-double the delayed reference beam to obtain a SHG reference beam;

[0046] The second optical path modulator is used to adjust the optical path between the BBO crystal and the photodetector so that the SHG reference beam output by the BBO crystal is input into the photodetector of the photodetection and closed-loop control component.

[0047] Further, the photoelectric detection and closed-loop control component includes: a photoelectric detector, a power amplifier, a power divider, a despreader, a phase-locked circuit and a frequency shift control quantity producer;

[0048] The photodetector is used to simultaneously receive the SHG signal beam carrying defect information in the outgoing light path as the signal light and the SHG reference beam as the local oscillator light for coherent detection and output a mixed signal;

[0049] A power amplifier, used for amplifying the power of the mixed signal;

[0050] The power divider is used to divide the amplified mixed signal into N mixed signals; each mixed signal has the same signal power;

[0051] The despreader is used to despread N mixed frequency signals respectively, each despread signal corresponds to a signal beam; the despread signal of each mixed frequency signal includes a SHG signal after the sample is irradiated by a signal beam modulated by a spread spectrum with the same pseudo-random sequence as that used for the despreading;

[0052] The phase-locked circuit is used to phase-lock the signals after despreading the N mixed signals, and output the frequency deviation value of each signal;

[0053] The frequency shift control amount generator is used to convert the frequency deviation value of the path signal into a frequency shift control amount through A / D conversion, and feed it back to the corresponding frequency shift module in the incident light path to control the frequency shift amount of the corresponding beam signal light beam and perform frequency homodyne control of each beam signal light beam. The present invention can achieve one of the following beneficial effects:

[0054] The multi-threaded detection method and system based on laser frequency modulation for second harmonic characterization of the present invention can process multiple SHG signals or perform multi-task operations at the same time, realize multi-threaded high-efficiency detection, and significantly improve the performance of optical characterization of the second harmonic system; and improve the quality and accuracy of the signal through modulation and demodulation technology, which is suitable for detection requiring high precision and high speed.

[0055] The present invention can realize multi-threaded simultaneous operation of second harmonic optics to characterize materials, which not only expands the application scope of nonlinear optics in multiple fields, but also provides new possibilities for efficient and rapid analysis of material properties, which is of great significance for scientific research and industrial applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] 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;

[0057] Figure 1 It is a flow chart of a multi-threaded detection method for realizing second harmonic characterization based on laser frequency modulation in an embodiment of the present invention;

[0058] Figure 2 is a spectrum analysis diagram of a homodyne detection signal in an embodiment of the present invention;

[0059] Figure 3 This is a multi-threaded detection system for realizing second harmonic characterization based on laser frequency modulation in an embodiment of the present invention.

[0060] Figure numerals: 1: laser; 100: main laser pulse; 2: beam splitter; 3: plane mirror; 4: local beam; 101: split beam; 5: signal generator; 6: delay; 7: feedback frequency fm; 8: frequency shifter; 9: BBO crystal; 10: power amplifier group; 11: sample; 12: photodetector; 13: power amplifier; 14: power divider; 15: despreader; 16: phase-locked circuit; 17: frequency shift control quantity producer. DETAILED DESCRIPTION

[0061] 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.

[0062] Embodiment 1

[0063] One embodiment of the present invention discloses a multi-threaded detection method for realizing second harmonic characterization based on laser frequency modulation, such as Figure 1 As shown, including:

[0064] Step S1, performing laser spread spectrum modulation on the signal beam after the main laser pulse is split in the incident light path to obtain N signal beams carrying frequency codes, focusing and irradiating the sample on the sample stage, and forming an SHG signal beam carrying defect information in the outgoing light path;

[0065] Step S2, after the main laser pulse is split, a reference beam is delayed and frequency-multiplied to form an SHG reference beam that matches the optical path of the SHG signal beam carrying defect information;

[0066] Step S3, performing photoelectric detection and signal splitting on the SHG signal beam carrying defect information and the reference beam to obtain N mixed signals;

[0067] Step S4, respectively despreading and phase-locking the N mixed signals to obtain the frequency deviation value of each signal light beam in the outgoing light path; converting the frequency deviation value into a frequency shift control value, and feeding it back to the incident light path to perform frequency homodyne control of each signal light beam;

[0068] Step S5: After homodyne control, each mixing signal is resolved and output to obtain the second harmonic representation of each signal light beam.

[0069] Specifically, step S1 includes:

[0070] 1) Splitting the main laser pulse into N signal beams and 1 reference beam through a beam splitter;

[0071] The main laser pulse is emitted by a laser having a very narrow spectral line, so that the phases of the signal light carrying the SHG signal and the local oscillator light are locked to each other.

[0072] 2) Generate N mutually orthogonal pseudo-random code sequences through a signal generator; correspond each pseudo-random code sequence to a signal light beam, input them into a frequency shifter, and use the pseudo-random code sequence to frequency encode the signal light beam to obtain N signal light beams carrying frequency codes;

[0073] 3) N signal beams carrying frequency codes are amplified and focused to illuminate the sample on the sample stage; the sample reflects the signal beam, forming an SHG signal beam carrying defect information in the outgoing light path.

[0074] More specifically, the signal generator generates N mutually orthogonal pseudo-random code sequences, and superimposes the pseudo-random codes on the signal light beam by cooperating with the frequency shifter, thereby completing the spread spectrum processing of the signal light beam. For example, one of the signal light beams sends bit 1. After the spread spectrum processing, the code chip sequence assigned to the light beam is 00011011, and the originally sent bit 1 is changed to the sent code chip sequence 00011011, and the sent bit 0 is changed to send 11100100 (its inverse code).

[0075] At the receiving end, each frequency-encoded signal beam uses the orthogonality of the code type to select the corresponding signal from the mixed signal through address recognition (correlation detection).

[0076] The mathematical formula for correlation detection of two orthogonal signals S1 and S2 is:

[0077]

[0078] The above formula shows that the inner product of orthogonal chip sequences is 0. For example, S 1 ·S 2=0, the normalized inner product of any chip vector and itself is 1, and it can be inferred that the inverse inner product of any chip sequence and its own chip sequence is -1 (S·S=1, S·S(inverse)=-1).

[0079] In this step, the frequency shifter is controlled by the mutually orthogonal N-channel pseudo-random code sequences generated by the signal generator to perform frequency encoding on each signal light beam to obtain a signal light beam after spectrum spread; the signal light beam after spectrum spread is then amplified by the laser amplifier to amplify the power of each laser channel and focused by the focusing mirror, and then irradiated to the sample, thereby better satisfying the generation conditions of the second harmonic SHG in the output light path.

[0080] Specifically, step S2 includes:

[0081] 1) A reference beam split from the beam splitter is delayed by a delay device to obtain a delayed reference beam;

[0082] 2) converting the delayed reference beam into a second harmonic by frequency doubling through a BBO crystal to obtain a SHG reference beam;

[0083] 3) Sending the SHG reference beam to the photodetector as a local oscillator beam to mix with the SHG signal beam carrying defect information in the outgoing optical path;

[0084] The delay time of the delay device is set so that the optical path lengths of the SHG signal light beam carrying defect information and the local oscillator light beam are consistent.

[0085] In this step, the reference beam passes through a time delay device with adjustable length, the purpose of which is to compensate for the optical path difference between the signal light and the reference light so that the phase difference remains stable; the reference beam after delay compensation is converted into a second harmonic by frequency doubling through a BBO crystal; finally, the outgoing beam carrying the SHG signal and the reference beam are received by the photodetector to achieve coherent detection.

[0086] Preferably, components for changing the propagation direction of the optical path, including a plane mirror, are added between the beam splitter and the delay device, and between the BBO crystal and the photodetector, so that the reference beam split by the beam splitter enters the delay device, and the SHG reference beam output by the BBO crystal enters the photodetector.

[0087] Specifically, step S3 includes:

[0088] 1) Through the photodetector, the SHG signal beam carrying defect information in the outgoing light path as the signal light and the SHG reference beam as the local oscillator light are simultaneously received for coherent detection, and a mixed signal is output;

[0089] 2) After the output mixed signal is power amplified, a power divider is used to divide the mixed signal into N mixed signals; the signal power of each mixed signal is the same.

[0090] In this step, the photodetector realizes coherent detection of signal light and local oscillator light, and converts the optical signal into an electrical signal, amplifies the power through a signal amplifier, and divides it according to the amount of detection light through a power divider; this provides a basis for the subsequent de-spreading of each signal light beam, extraction of second harmonic information, and closed-loop control of the frequency.

[0091] Specifically, step S4 includes:

[0092] In step S4,

[0093] 1) Despreading the N mixed signals by a despreader to obtain N despread signals;

[0094] Based on the orthogonality of the N pseudo-random code sequences in the incident light path, the same N pseudo-random code sequences as the incident light path are used in the despreader to despread the N mixed signals respectively to obtain N despread signals; each despread signal corresponds to a signal light beam, including the SHG signal carried by the signal light beam after irradiating the sample;

[0095] 2) After the N-channel despread signals are phase-locked by the phase-locked circuit, the frequency deviation value of each signal light beam in the outgoing light path is obtained;

[0096] 3) The frequency deviation value of each signal beam is converted into a frequency shift control value through A / D conversion, and fed back to the frequency shifter in the incident light path to control the frequency shift amount of each signal beam and perform zero-difference control on the frequency of each signal beam.

[0097] In this step, the demodulator demodulates the frequency code carried in the branch mixing signal, distinguishes the signal information of different branches, and thus extracts the second harmonic information of the sample carried by each detection light in the outgoing light path, and through frequency phase locking and frequency shift control amount conversion, it is connected to the frequency shifter to form a closed-loop control, and then analyzes and processes the information at different sites of the sample, and finally realizes multi-threaded optical characterization.

[0098] The signal beam with superimposed pseudo-random code sequence is: S 1 , S 2 , S 3 …S N ,

[0099] Signal beam S 1 The chip sequence in is: A1 1 +A1 2 +A1 3 +A1 4 +…+A1m ;

[0100] …

[0101] Signal beam S N The chip sequence in is: AN 1 +AN 2 +AN 3 +AN 4 +…+AN m ;

[0102] N is the number of pseudo-random code sequences; m is the number of chips in the pseudo-random code sequence.

[0103] At this time, the mixed signal can be expressed as:

[0104] (A1 1 +A2 1 +...+AN 1 )+(A1 2 +A2 2 +...+AN 2 )+...+(A1 m +A2 m +...+AN m )

[0105] At this time, the despreader will S 1 When the signal is separated,

[0106] The inner product of the chip sequence of the mixing signal and the S1 signal at the despreader port is:

[0107] (S 1 +S 2 +S 3 +...+S N )*(A1 1 +A2 1 +...+AN 1 )

[0108] =A1 1 ·(A1 1 +A2 1 +...+AN 1 )+A1 2 ·(A1 2 +A2 2 +...+AN 2 )+...+A1 m ·(A1 m +A2 m +...+AN m )

[0109] ={A1 1 A11 +A1 1 A2 1 +...+A1 1 AN+...+A1 m A1 m +A1 m A2 m +...+A1 m ·AN m}

[0110] =S1·S1+S1·S2+S1·S3+...+S1·S N =1

[0111] It can be seen from the formula that the despreader receiver can despread the information sent by the transmitter after knowing the code chip sequence spread by the transmitter in advance. No matter how complex the mixed signal is, the receiver can obtain the sent information once it knows the code chip sequence of the transmitter.

[0112] In this embodiment, the frequency of the local oscillator light is the same as the frequency of the signal light, and the phases are locked to each other, and the output signal frequency is 0, which is homodyne detection.

[0113] In step S5, each mixed signal is discriminated by a discriminator circuit, and then the second harmonic signal of each signal beam irradiating the sample is directly output.

[0114] Furthermore, the phase-locked circuit feeds back frequency and information to the signal generator and the optical frequency shifter, continuously monitors the phase difference between the local oscillator light and the signal light, and dynamically adjusts the phase of the signal light to keep their frequency and phase difference at zero, thus achieving zero-difference control.

[0115] In a specific embodiment, the spectrum analysis diagram of the homodyne detection signal is as follows: Figure 2 As shown, E s is the spectrum of the signal light, where ω s Indicates the center frequency of the signal light. The multiple peaks of the spectrum represent different frequency components of the signal light, and these different frequency components carry information. L This is the spectrum of the local oscillator light, ω L is the frequency of the local oscillator light. Compared with the spectrum of the signal light, the spectrum of the local oscillator light is very narrow, representing a very stable and single-frequency light source. In the homodyne detection system of coherent detection, the local oscillator light usually needs to have an extremely narrow linewidth to accurately mix with the signal light. E represents the signal spectrum after the signal light and the local oscillator light are mixed. In homodyne detection, the center frequency ω of the signal light is s and the frequency of the local oscillator light ω LAfter mixing, the frequency components in the signal light are transferred to the baseband (i.e., close to zero frequency), so that the second harmonic information of the sample carried in the probe light can be directly extracted. The figure shows the spectrum distribution of the signal after mixing, showing several peaks near the baseband, which correspond to the frequency components of the signal light spectrum.

[0116] In summary, the embodiments of the present invention can achieve the following effects:

[0117] The embodiments of the present invention can process multiple SHG signals simultaneously or perform multi-tasking operations, realize multi-threaded high-efficiency detection, and significantly improve the performance of optical characterization of the second harmonic system; and improve the quality and accuracy of the signal through modulation and demodulation technology, which is suitable for detection requiring high precision and high speed.

[0118] The embodiments of the present invention can realize multi-threaded simultaneous operation of second harmonic optics to characterize materials, which not only expands the application scope of nonlinear optics in multiple fields, but also provides new possibilities for efficient and rapid analysis of material properties, which is of great significance for scientific research and industrial applications.

[0119] Embodiment 2

[0120] This embodiment discloses a multi-threaded detection system based on laser frequency modulation to realize second harmonic characterization. Figure 3 As shown, it includes: an incident light path component, a reference light path component, a photoelectric detection and closed-loop control component and a characterization output component; wherein,

[0121] The incident light path component is used to perform laser spread spectrum modulation on the signal light beam after the main laser pulse is split in the incident light path to obtain N signal light beams carrying frequency codes, and then focus and irradiate the sample on the sample stage; thereby forming an SHG signal light beam carrying defect information in the outgoing light path;

[0122] A reference optical path component is used to delay and frequency-double a reference beam after the main laser pulse is split, so as to form an SHG reference beam that matches the optical path of the SHG signal beam carrying defect information;

[0123] The photoelectric detection and closed-loop control component is used to perform photoelectric detection and signal splitting on the SHG signal beam and the reference beam carrying defect information to obtain N-channel mixed signals; and respectively despread and phase-lock the N-channel mixed signals to obtain the frequency deviation value of each signal beam in the outgoing optical path; the frequency deviation value is converted into a frequency shift control amount, and fed back to the incident optical path to perform frequency homodyne control of each signal beam;

[0124] The characterization output component is used to output the second harmonic characterization obtained by solving each mixing signal after homodyne control.

[0125] Specifically, the incident light path component includes a laser, a beam splitter, a signal generator, a frequency shifter, a power amplifier group and a focusing lens; wherein,

[0126] The laser is used to generate a main laser pulse;

[0127] The beam splitter is used to split the main laser pulse into N signal beams and 1 reference beam;

[0128] The signal generator is used to generate N mutually orthogonal pseudo-random code sequences;

[0129] The frequency shifter comprises N frequency shift modules; each frequency shift module takes a pseudo-random code sequence and a signal beam as input, uses the input pseudo-random code sequence to frequency encode the input signal beam in the frequency shift module, and outputs a signal beam carrying the frequency code;

[0130] The power amplifier group includes N amplifiers, which are respectively connected to the N frequency shift modules to amplify the optical power of the signal light beams carrying the frequency code output by the frequency shift modules;

[0131] The focusing lens is used to focus the signal light beam carrying the frequency code after power amplification to irradiate the sample on the sample stage;

[0132] The sample reflects the signal beam, forming an SHG signal beam carrying defect information in the outgoing light path.

[0133] Specifically, the reference optical path component includes a first optical path adjuster, a delay device, a BBO crystal and a second optical path modulator;

[0134] The first optical path adjuster is used to adjust the optical path between the beam splitter and the delay device so that the reference beam split by the beam splitter is input into the delay device;

[0135] The delay device is used to control the delay of the reference beam to obtain a delayed reference beam;

[0136] The BBO crystal is used to frequency-double the delayed reference beam to obtain a SHG reference beam;

[0137] The second optical path modulator is used to adjust the optical path between the BBO crystal and the photodetector so that the SHG reference beam output by the BBO crystal is input into the photodetector of the photodetection and closed-loop control component.

[0138] Specifically, the photoelectric detection and closed-loop control components include a photoelectric detector, a power amplifier, a power divider, a despreader, a phase-locked circuit, and a frequency shift control quantity producer;

[0139] The photodetector is used to simultaneously receive the SHG signal beam carrying defect information in the outgoing light path as the signal light and the SHG reference beam as the local oscillator light for coherent detection and output a mixed signal;

[0140] A power amplifier, used for amplifying the power of the mixed signal;

[0141] The power divider is used to divide the amplified mixed signal into N mixed signals; each mixed signal has the same signal power;

[0142] The despreader is used to despread N mixed frequency signals respectively, each despread signal corresponds to a signal beam; the despread signal of each mixed frequency signal includes a SHG signal after the sample is irradiated by a signal beam modulated by a spread spectrum with the same pseudo-random sequence as that used for the despreading;

[0143] The phase-locked circuit is used to phase-lock the signals after despreading the N mixed signals, and output the frequency deviation value of each signal;

[0144] The frequency shift control amount generator is used to convert the frequency deviation value of the path signal into a frequency shift control amount through A / D conversion, and feed it back to the corresponding frequency shift module in the incident light path to control the frequency shift amount of the corresponding beam signal light beam and perform frequency zero difference control of each beam signal light beam.

[0145] The characterization output component directly outputs the second harmonic signal of each signal light beam irradiating the sample after frequency discrimination of each mixed signal through a frequency discrimination circuit.

[0146] 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 multi-threaded detection method for second harmonic characterization based on laser frequency modulation, characterized in that: include: Step S1, performing laser spread spectrum modulation on the signal beam after the main laser pulse is split in the incident light path to obtain N signal beams carrying frequency codes, focusing and irradiating the sample on the sample stage, and forming an SHG signal beam carrying defect information in the outgoing light path; Step S2, after the main laser pulse is split, a reference beam is delayed and frequency-multiplied to form an SHG reference beam that matches the optical path of the SHG signal beam carrying defect information; Step S3, performing photoelectric detection and signal splitting on the SHG signal beam carrying defect information and the reference beam to obtain N mixed signals; Step S4, respectively despreading and phase-locking the N mixed signals to obtain the frequency deviation value of each signal light beam in the outgoing light path; converting the frequency deviation value into a frequency shift control value, and feeding it back to the incident light path to perform frequency homodyne control of each signal light beam; Step S5: After homodyne control, each mixing signal is resolved and output to obtain the second harmonic representation of each signal light beam.

2. The multi-thread detection method based on laser frequency modulation to realize second harmonic characterization according to claim 1 is characterized in that: Step S1 includes: 1) Splitting the main laser pulse into N signal beams and 1 reference beam through a beam splitter; 2) Generate N mutually orthogonal pseudo-random code sequences through a signal generator; correspond each pseudo-random code sequence to a signal light beam, input them into a frequency shifter, and use the pseudo-random code sequence to frequency encode the signal light beam to obtain N signal light beams carrying frequency codes; 3) N signal beams carrying frequency codes are amplified and focused to illuminate the sample on the sample stage; the sample reflects the signal beam, forming an SHG signal beam carrying defect information in the outgoing light path.

3. The multi-thread detection method based on laser frequency modulation to realize second harmonic characterization according to claim 2 is characterized in that: Step S2 includes: 1) A reference beam split from the beam splitter is delayed by a delay device to obtain a delayed reference beam; 2) converting the delayed reference beam into a second harmonic by frequency doubling through a BBO crystal to obtain a SHG reference beam; 3) Sending the SHG reference beam to the photodetector as a local oscillator beam to mix with the SHG signal beam carrying defect information in the outgoing optical path; By setting the delay time of the delay device, the optical path lengths of the signal beam and the local oscillator beam are made consistent.

4. The multi-thread detection method based on laser frequency modulation to realize second harmonic characterization according to claim 3 is characterized in that: Components for changing the propagation direction of the optical path, including a plane mirror, are added between the beam splitter and the delay device, and between the BBO crystal and the photodetector, so that the reference beam split by the beam splitter enters the delay device, and the SHG reference beam output by the BBO crystal enters the photodetector.

5. The multi-thread detection method based on laser frequency modulation to realize second harmonic characterization according to claim 3 is characterized in that: In step S3, 1) Through the photodetector, the SHG signal beam carrying defect information in the outgoing light path as the signal light and the SHG reference beam as the local oscillator light are simultaneously received for coherent detection, and a mixed signal is output; 2) After the output mixed signal is power amplified, a power divider is used to divide the mixed signal into N mixed signals; The signal power of each mixed signal is the same.

6. The multi-thread detection method based on laser frequency modulation to realize second harmonic characterization according to claim 5, characterized in that: In step S4, 1) Despreading the N mixed signals by a despreader to obtain N despread signals; Based on the orthogonality of the N pseudo-random code sequences in the incident light path, the same N pseudo-random code sequences as the incident light path are used in the despreader to despread the N mixed signals respectively to obtain N despread signals; each despread signal corresponds to a signal light beam, including the SHG signal carried by the signal light beam after irradiating the sample; 2) After the N-channel despread signals are phase-locked by the phase-locked circuit, the frequency deviation value of each signal light beam in the outgoing light path is obtained; 3) The frequency deviation value of each signal beam is converted into a frequency shift control value through A / D conversion, and fed back to the frequency shifter in the incident light path to control the frequency shift amount of each signal beam and perform zero-difference control on the frequency of each signal beam.

7. A multi-threaded high-efficiency characterization system for second harmonic based on laser frequency modulation, characterized in that: include: Incident light path component, reference light path component, photoelectric detection and closed-loop control component and characterization output component; wherein, The incident light path component is used to perform laser spread spectrum modulation on the signal light beam after the main laser pulse is split in the incident light path to obtain N signal light beams carrying frequency codes, and then focus and irradiate the sample on the sample stage; thereby forming an SHG signal light beam carrying defect information in the outgoing light path; A reference optical path component is used to delay and frequency-double a reference beam after the main laser pulse is split, so as to form an SHG reference beam that matches the optical path of the SHG signal beam carrying defect information; The photoelectric detection and closed-loop control component is used to perform photoelectric detection and signal splitting on the SHG signal beam and the reference beam carrying defect information to obtain N-channel mixed signals; and respectively despread and phase-lock the N-channel mixed signals to obtain the frequency deviation value of each signal beam in the outgoing optical path; the frequency deviation value is converted into a frequency shift control amount, and fed back to the incident optical path to perform frequency homodyne control of each signal beam; The characterization output component is used to output the second harmonic characterization obtained by solving each mixing signal after homodyne control.

8. The laser frequency modulation-based second harmonic multi-threaded efficient characterization system according to claim 7 is characterized in that: The incident light path components include: a laser, a beam splitter, a signal generator, a frequency shifter, a power amplifier group and a focusing lens; wherein, The laser is used to generate a main laser pulse; The beam splitter is used to split the main laser pulse into N signal beams and 1 reference beam; The signal generator is used to generate N mutually orthogonal pseudo-random code sequences; The frequency shifter comprises N frequency shift modules; each frequency shift module takes a pseudo-random code sequence and a signal beam as input, uses the input pseudo-random code sequence to frequency encode the input signal beam in the frequency shift module, and outputs a signal beam carrying the frequency code; The power amplifier group includes N amplifiers, which are respectively connected to the N frequency shift modules to amplify the optical power of the signal light beams carrying the frequency code output by the frequency shift modules; The focusing lens is used to focus the signal light beam carrying the frequency code after power amplification to irradiate the sample on the sample stage; The sample reflects the signal beam, forming an SHG signal beam carrying defect information in the outgoing light path.

9. The laser frequency modulation-based second harmonic multi-threaded efficient characterization system according to claim 8, characterized in that: The reference optical path component comprises: a first optical path adjuster, a delay device, a BBO crystal and a second optical path modulator; The first optical path adjuster is used to adjust the optical path between the beam splitter and the delay device so that the reference beam split by the beam splitter is input into the delay device; The delay device is used to control the delay of the reference beam to obtain a delayed reference beam; The BBO crystal is used to frequency-double the delayed reference beam to obtain a SHG reference beam; The second optical path modulator is used to adjust the optical path between the BBO crystal and the photodetector so that the SHG reference beam output by the BBO crystal is input into the photodetector of the photodetection and closed-loop control component.

10. The laser frequency modulation-based second harmonic multi-threaded efficient characterization system according to claim 9, characterized in that: The photoelectric detection and closed-loop control components include: a photoelectric detector, a power amplifier, a power divider, a despreader, a phase-locked circuit and a frequency shift control quantity generator; The photodetector is used to simultaneously receive the SHG signal beam carrying defect information in the outgoing light path as the signal light and the SHG reference beam as the local oscillator light for coherent detection and output a mixed signal; A power amplifier, used for amplifying the power of the mixed signal; The power divider is used to divide the amplified mixed signal into N mixed signals; each mixed signal has the same signal power; The despreader is used to despread N mixed frequency signals respectively, each despread signal corresponds to a signal beam; the despread signal of each mixed frequency signal includes a SHG signal after the sample is irradiated by a signal beam modulated by a spread spectrum with the same pseudo-random sequence as that used for the despreading; The phase-locked circuit is used to phase-lock the signals after despreading the N mixed signals, and output the frequency deviation value of each signal; The frequency shift control amount generator is used to convert the frequency deviation value of the path signal into a frequency shift control amount through A / D conversion, and feed it back to the corresponding frequency shift module in the incident light path to control the frequency shift amount of the corresponding beam signal light beam and perform frequency zero difference control of each beam signal light beam.

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