A nonlinear grating processing technology based on pyroelectric field induced polarization

Abstract

The present invention discloses a nonlinear grating processing technology based on pyroelectric field induced polarization. The present invention firstly uses a laser processing module to scribe lines in a nonlinear crystal along the crystal axis direction, thereby forming two groups of aligned grating structures in the nonlinear crystal; secondly, a heat treatment module is used to heat the nonlinear crystal to 180-240°C, and then the environment where the nonlinear crystal is located is evacuated and cooled to room temperature, so that a pyroelectric field opposite to the spontaneous polarization direction is generated during the cooling process, thereby reversing the ferroelectric domains between the two groups of grating structures of the nonlinear crystal along the crystal axis direction to form a nonlinear polarization grating, and finally an optical characterization module is used to collect the fundamental wave and second harmonic signals of the laser processing area where the grating structure of the nonlinear crystal is located and the domain growth area where the nonlinear polarization grating is located, to verify the formation of the nonlinear grating structure. Compared with the prior art, the present invention has a greater processing depth and more uniform polarized ferroelectric domains.

Description

Technical Field

[0001] The present invention relates to a ferroelectric material domain control technology, and in particular to a nonlinear grating processing technology based on pyroelectric field induced polarization. Background Art

[0002] Lithium niobate has excellent acousto-optic, electro-optic and nonlinear properties and is an important optical material. The periodically distributed nonlinear coefficient can provide additional reciprocal lattice vectors to compensate for the wave vector mismatch in the frequency conversion process, ensuring that the nonlinear conversion efficiency is proportional to the square of the crystal length, and achieving quasi-phase matching. Quasi-phase matching overcomes the walk-off effect in birefringence phase matching, making periodically poled lithium niobate crystals the most popular nonlinear material, thus inspiring researchers to conduct in-depth research on ferroelectric domain control technology. Mature electric field polarization technology can only prepare one-dimensional and two-dimensional nonlinear photonic crystals. In recent years, femtosecond laser fixed-point control of lithium niobate ferroelectric domain technology has successfully achieved three-dimensional patterned modulation of χ(2), laying a technical foundation for the development of functional three-dimensional nonlinear photonic crystals. However, when femtosecond pulse light converges from air to the inside of the lithium niobate crystal, it is affected by interface aberrations and birefringence, causing the light spot focused inside the crystal to be severely distorted, restricting processing in the depth direction. Summary of the invention

[0003] In view of the problems existing in the prior art, the present invention provides a nonlinear grating processing system and method based on pyroelectric field induced polarization, which has a greater processing depth and more uniform polarized ferroelectric domains.

[0004] In order to achieve the above-mentioned object of the invention, the present invention provides a nonlinear grating processing system based on pyroelectric field induced polarization, comprising:

[0005] A laser processing module is used to scribe lines in the nonlinear crystal along the crystal axis direction, thereby forming two sets of aligned grating structures in the nonlinear crystal;

[0006] A heat treatment module is used to heat the nonlinear crystal to 180-240°C, then evacuate the environment where the nonlinear crystal is located, and cool it to room temperature, so that a pyroelectric field opposite to the spontaneous polarization direction is generated during the cooling process, thereby reversing the ferroelectric domains between the two groups of grating structures of the nonlinear crystal along the crystal axis direction to form a nonlinear polarization grating;

[0007] The optical characterization module is used to collect the fundamental wave and second harmonic signals in the laser processing area where the grating structure of the nonlinear crystal is located and the domain growth area where the nonlinear polarization grating is located to verify the formation of the nonlinear grating structure.

[0008] Preferably, the laser processing module specifically includes:

[0009] A first laser, used for emitting laser light along the crystal axis direction;

[0010] An optical shutter, placed behind the first laser emission port, is used to control the time when the laser passes through;

[0011] The gradient attenuation sheet is placed behind the optical shutter to attenuate the passing laser energy;

[0012] The first half-wave plate is placed behind the gradient attenuation plate and is used to change the polarization direction of the laser so that the polarization direction is along the x-axis direction;

[0013] A first objective lens is disposed behind the first half-wave plate and is used to tightly focus the light beam emitted by the first laser so that the focus is located within the nonlinear crystal;

[0014] A three-dimensional nano-translation stage is placed on which a nonlinear crystal is placed to move the position of the nonlinear crystal so that the laser emitted by the first laser scribes from deep to shallow along the crystal axis direction of the nonlinear crystal, forming two groups of grating structures aligned along the y-axis direction.

[0015] Preferably, the heat treatment module specifically includes:

[0016] A vacuum temperature control platform, in which a nonlinear crystal with a grating structure is placed, is used to heat the nonlinear crystal to 180-240° C. at a first preset speed, then evacuate the vacuum temperature control platform to reach a preset vacuum degree, and then cool it to room temperature at a second preset speed, thereby forming a nonlinear polarization grating between two groups of grating structures of the nonlinear crystal;

[0017] Polarized light microscopy system is used to perform real-time imaging of the ferroelectric domain change process between two sets of grating structures in nonlinear crystals.

[0018] Preferably, the optical characterization module specifically includes:

[0019] A second laser is used to emit laser light along the x-axis direction;

[0020] A second half-wave plate is disposed behind the emission port of the second laser and is used to change the polarization direction of the laser light emitted by the second laser so that the polarization direction of the laser light is along the z-axis direction;

[0021] A lens, disposed behind the second half-wave plate, for focusing the laser light emitted by the second laser so that the focal point is located in the nonlinear crystal laser processing area;

[0022] The receiving screen is used to receive the diffraction spots passing through the laser processing area where the nonlinear crystal grating structure is located and the domain growth area where the nonlinear polarization grating is located, obtain the fundamental wave and the second harmonic signal, and verify the formation of the nonlinear grating structure.

[0023] Preferably, the polarizing microscope system specifically comprises:

[0024] An illumination light source, used for emitting white light toward the grating structure surface of the nonlinear crystal;

[0025] A first polarizer is placed below the nonlinear crystal and above the illumination light source, and is used to convert the white light emitted by the illumination light source into linearly polarized light;

[0026] A second objective lens is located above the nonlinear crystal and is used to diffuse the light passing through the processing area of ​​the nonlinear crystal;

[0027] A second polarizer, the polarization direction of which is orthogonal to that of the first polarizer, is used to change the polarization direction of light;

[0028] CCD for real-time imaging of the nonlinear crystal laser processing area.

[0029] The present invention also provides a nonlinear grating processing method based on pyroelectric field induced polarization, comprising:

[0030] Inscribe lines along the crystal axis in the nonlinear crystal, thereby forming two groups of aligned grating structures in the nonlinear crystal;

[0031] The nonlinear crystal is heated to 180-240°C, and then the environment where the nonlinear crystal is located is evacuated and cooled to room temperature, so that a pyroelectric field opposite to the spontaneous polarization direction is generated during the cooling process, thereby reversing the ferroelectric domains between the two groups of grating structures of the nonlinear crystal along the crystal axis direction to form a nonlinear polarization grating;

[0032] The fundamental wave and second harmonic signals of the laser processing area where the grating structure of the nonlinear crystal is located and the domain growth area where the nonlinear polarization grating is located are collected to verify the formation of the nonlinear grating structure.

[0033] Furthermore, the nonlinear crystal is heated to 180-240° C., and then the environment where the nonlinear crystal is located is evacuated and cooled to room temperature, specifically including:

[0034] The nonlinear crystal with a grating structure is heated to 180-240° C. at a first preset speed, and then evacuated to make the inside of the vacuum temperature control platform reach a preset vacuum degree, and then cooled to room temperature at a second preset speed.

[0035] Preferably, the preset vacuum degree is 76 torr. Preferably, the nonlinear crystal is heated to 200-220° C. Preferably, the period of the two groups of grating structures is in the micron order, and the interval is in the micron order.

[0036] Compared with the prior art, the present invention has the following beneficial effects: the present invention combines femtosecond laser direct writing with heat treatment to generate a pyroelectric field to induce domain inversion of nonlinear crystals such as lithium niobate, thereby achieving domain polarization. The technology does not require any external electric field, has a greater processing depth, and polarizes ferroelectric domains more uniformly, and can process large-scale grating structures in bulk lithium niobate and other nonlinear crystals. In addition, due to the introduction of a polarizing microscope system, the change process of the ferroelectric domain can also be detected in real time. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 is a system block diagram of a nonlinear grating processing system based on pyroelectric field induced polarization provided by an embodiment of the present invention;

[0038] Figure 2 This is a diagram of the domain growth dynamics process with a period of 8 microns in the y direction during the annealing process;

[0039] Figure 3 It is an optical representation diagram. DETAILED DESCRIPTION

[0040] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] The embodiment of the present invention provides a nonlinear grating processing system based on pyroelectric field induced polarization, such as Figure 1 As shown, including:

[0042] A laser processing module is used to scribe lines in the nonlinear crystal along the crystal axis direction, thereby forming two sets of aligned grating structures in the nonlinear crystal;

[0043] A heat treatment module is used to heat the nonlinear crystal to 180-240°C, then evacuate the environment where the nonlinear crystal is located, and cool it to room temperature, so that a pyroelectric field opposite to the spontaneous polarization direction is generated during the cooling process, thereby reversing the ferroelectric domains between the two groups of grating structures of the nonlinear crystal along the crystal axis direction to form a nonlinear polarization grating;

[0044] The optical characterization module is used to collect the fundamental wave and second harmonic signals in the laser processing area where the grating structure of the nonlinear crystal is located and the domain growth area where the nonlinear polarization grating is located to verify the formation of the nonlinear grating structure.

[0045] Wherein, the laser processing module specifically includes:

[0046] Laser 1, used for emitting laser light along the crystal axis (z axis); specifically, a laser with a wavelength of 800 nm, a pulse width of 34 fs, and a repetition frequency of 1 kHz can be used;

[0047] The optical shutter 1 is placed behind the emission port of the laser 1 and is used to control the time when the laser passes through;

[0048] The gradient attenuation sheet 1 is placed behind the optical shutter 1 and is used to attenuate the laser energy passing through;

[0049] The half-wave plate 1 is placed behind the gradient attenuation plate 1 and is used to change the polarization direction of the laser so that the polarization direction is along the x-axis direction;

[0050] The objective lens 1 is placed behind the half-wave plate 1 and is used to tightly focus the light beam emitted by the laser 1 so that the focus is located in the nonlinear crystal and the beam waist radius is 1 micron; specifically, an objective lens with a numerical aperture of 0.75 can be selected;

[0051] A three-dimensional nano-translation stage is placed on which a nonlinear crystal is placed to move the position of the nonlinear crystal so that the laser emitted by the laser 1 is engraved from deep to shallow along the crystal axis direction of the nonlinear crystal, forming two groups of grating structures aligned along the y-axis direction.

[0052] Wherein, the heat treatment module specifically includes:

[0053] A vacuum temperature control platform, in which a nonlinear crystal with a grating structure is placed, is used to heat the nonlinear crystal to 180-240° C. at a first preset speed, then evacuate the vacuum temperature control platform to reach a preset vacuum degree, and then cool it to room temperature at a second preset speed, thereby forming a nonlinear polarization grating between two groups of grating structures of the nonlinear crystal;

[0054] Polarized light microscopy system is used to perform real-time imaging of the ferroelectric domain change process between two sets of grating structures in nonlinear crystals.

[0055] Wherein, the polarizing microscope system specifically comprises:

[0056] An illumination light source, used for emitting white light toward the grating structure surface of the nonlinear crystal;

[0057] Polarizer 1, placed below the nonlinear crystal and above the illumination light source, used to convert the white light emitted by the illumination light source into linearly polarized light;

[0058] Objective lens 2, located above the nonlinear crystal, is used to diffuse the light passing through the processing area of ​​the nonlinear crystal. Specifically, an objective lens with a numerical aperture of 0.25 can be used;

[0059] Polarizer 2, whose polarization direction is orthogonal to that of polarizer 1, is used to change the polarization direction of light;

[0060] CCD for real-time imaging of the nonlinear crystal laser processing area.

[0061] Wherein, the optical characterization module specifically includes:

[0062] Laser 2, used for emitting laser light along the x-axis direction; specifically, a laser with a wavelength of 800 nm, a pulse width of 140 fs, a repetition frequency of 800 MHz, and a power of 600-800 mW can be selected;

[0063] Half-wave plate 2, with a focal length of micrometers, is placed behind the emission port of laser 2 and is used to change the polarization direction of the laser emitted by laser 2 so that the polarization direction of the laser is along the z-axis direction, and the beam waist radius is 80 micrometers;

[0064] A lens, placed behind the half-wave plate 2, is used to focus the laser emitted by the laser 2 so that the focus is located in the nonlinear crystal laser processing area;

[0065] The receiving screen is used to receive the diffraction spots passing through the laser processing area where the nonlinear crystal grating structure is located and the domain growth area where the nonlinear polarization grating is located, obtain the fundamental wave and the second harmonic signal, and verify the formation of the nonlinear grating structure.

[0066] The embodiment of the present invention further provides a nonlinear grating processing method based on pyroelectric field induced polarization, comprising the following steps:

[0067] S1. Lines are engraved in the nonlinear crystal along the crystal axis direction, thereby forming two groups of aligned grating structures in the nonlinear crystal, wherein the periods of the two groups of grating structures are in the micrometer order and the intervals are in the micrometer order.

[0068] S2. The nonlinear crystal is heated to 180-240°C, and then the environment of the nonlinear crystal is evacuated and cooled to room temperature, so that a pyroelectric field opposite to the spontaneous polarization direction is generated during the cooling process, thereby reversing the ferroelectric domains between the two groups of grating structures of the nonlinear crystal along the crystal axis direction to form a nonlinear polarization grating.

[0069] In specific implementation, the nonlinear crystal with a grating structure can be heated to 180-240°C, preferably 200-220°C, at a first preset speed, and then evacuated to make the inside of the vacuum temperature control platform reach a preset vacuum degree, and then cooled to room temperature at a second preset speed. The first preset speed is a slow speed, lower than 30°C / min, the second preset speed is about 30°C / min, the preset vacuum degree is about 76torr, and the room temperature is about 20°C. The temperature at which the nonlinear crystal is heated is

[0070] S3. Collect fundamental and second harmonic signals from the laser processing area where the grating structure of the nonlinear crystal is located and the domain growth area where the nonlinear polarization grating is located to verify the formation of the nonlinear grating structure.

[0071] The following experiment is conducted on a 5% magnesium-doped lithium niobate crystal. Laser 1 emits a laser with a wavelength of 800nm, a pulse width of 34fs, and a repetition frequency of 1kHz along the z direction. After passing through half-wave plate 1, the polarization changes to the z direction. After the laser passes through objective lens 1 with a numerical aperture of 0.75, it is focused onto the 5% magnesium-doped lithium niobate crystal. Labview software is used to control the travel of the three-dimensional nano-translation stage, so that the laser is engraved along the z direction to form a line. Figure 2 The grating structure is shown. The grating structure consists of two groups of gratings aligned along the y direction, with a line length of 50 microns along the z direction, a period of micron order, and a spacing of 100 microns between the two groups of gratings. During the entire processing process, the laser focus moves from deep (210 microns) to shallow (10 microns). In this process, the energy of the laser is gradually changed from 600nJ to 300nJ using a gradient attenuation plate 1.

[0072] Next, the laser-processed lithium niobate crystal is placed on a vacuum temperature control platform, slowly heated to 180-240°C, then evacuated to a vacuum degree of 76torr, and then cooled to room temperature at a rate of 30°C / min. During the cooling process, a pyroelectric field opposite to the spontaneous polarization direction is generated, which will cause the ferroelectric domain to reverse along the z direction from the laser processing area to form a nonlinear polarization grating. The lithium niobate crystal is illuminated by an illumination light source, and orthogonal polarizers 1 and 2 are placed above and below the lithium niobate crystal, respectively, to ensure that only the laser processing area and the domain reversal area can be illuminated, and then magnified by an objective lens with an NA of 0.25, and finally collected by the CCD to achieve real-time observation of the domain structure of the lithium niobate crystal.

[0073] Finally, laser 2 emits a laser with a wavelength of 800nm, a pulse width of 140fs, a repetition frequency of 800MHz, and a power of 800mW along the x direction. The polarization direction of the laser changes to the z direction through half-wave plate 2, and then is focused by a lens with a focal length of 100mm onto the lithium niobate crystal, and the fundamental wave and second harmonic signals are observed on the receiving screen.

[0074] Figure 2 The dynamic evolution of ferroelectric domains in lithium niobate crystals with a period of 8 microns in the y direction is shown. From left to right, the domain structures of lithium niobate crystals during annealing cooling from 120°C to 20°C, recorded every 30 seconds, show that under the action of the pyroelectric field, the inversion domains preferentially grow from the grating deeper from the surface along the z direction toward the surface, gradually covering the entire structure.

[0075] Table 1 is a table of ferroelectric domain polarization effects of gratings with different periods in the y direction in 5% magnesium-doped lithium niobate crystals corresponding to different quenching temperatures. The temperature range is cooled from 180, 200, 220 and 240°C to 20°C, and the corresponding ferroelectric domain polarization probabilities when the periods are 4, 6, 8 and 10 microns respectively. It can be seen from the table that the smaller the period, the higher the control requirements for the temperature range. Taking a 4-micron period as an example, when the temperature is cooled from below 180°C to 20°C, it is difficult for the ferroelectric domain to be polarized; when the temperature is above 220°C and cooled to 20°C, some adjacent polarized ferroelectric domains will merge together and be difficult to distinguish. Different cycles have different ranges of heat treatment. The heating temperature is preferably 200-220°C.

[0076] Table 1 Ferroelectric domain polarization effect of different period gratings corresponding to different quenching temperatures

[0077] 4 microns 6 microns 8 microns 10 microns 180℃-20℃ 20％ 29％ 40％ 69％ 200℃-20℃ 80％ 62％ 75％ 100％ 220℃-20℃ Partial adhesion 74％ 90％ 100％ 240℃-20℃ Partial adhesion 92％ 95％ 100％

[0078] Figure 3 Diffraction pattern of a grating with a period of 16 microns. Figure 3 (a) shows the diffraction spot pattern of the light beam passing through the femtosecond laser processing area. Except for the spot in the middle where no diffraction occurs, the red and purple spots appear alternately on both sides periodically, and the purple period is half of the red period. This shows that femtosecond laser processing will change the refractive index while changing the nonlinear coefficient of the lithium niobate crystal. The fundamental wave and second harmonic diffraction exist simultaneously in this area. When the light beam passes through the domain growth area, the diffraction phenomenon is as follows Figure 3 As shown in (b), the red light does not diffract, while the purple light diffraction phenomenon is significantly enhanced. This shows that the annealing process will only change the nonlinear coefficient of the crystal, but will not change the linear coefficients such as the refractive index, which is consistent with the expected effect.

[0079] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish different objects rather than to describe a specific order. The reference to "embodiment" in this article means that the specific features, structures or characteristics described in conjunction with the embodiment may be included in at least one embodiment of the present invention. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

Claims

1. A nonlinear grating processing system based on pyroelectric field induced polarization, characterized in that: include: A laser processing module is used to scribe lines in the nonlinear crystal along the crystal axis direction, thereby forming two sets of aligned grating structures in the nonlinear crystal; A heat treatment module is used to heat the nonlinear crystal to 180-240°C, then evacuate the environment where the nonlinear crystal is located, and cool it to room temperature, so that a pyroelectric field opposite to the spontaneous polarization direction is generated during the cooling process, thereby reversing the ferroelectric domains between the two groups of grating structures of the nonlinear crystal along the crystal axis direction to form a nonlinear polarization grating; Optical characterization module, used to collect fundamental and second harmonic signals in the laser processing area where the grating structure of the nonlinear crystal is located and the domain growth area where the nonlinear polarization grating is located, to verify the formation of the nonlinear grating structure; Wherein, the laser processing module specifically includes: A first laser, used for emitting laser light along the crystal axis direction; An optical shutter, placed behind the first laser emission port, is used to control the time when the laser passes through; The gradient attenuation sheet is placed behind the optical shutter to attenuate the passing laser energy; The first half-wave plate is placed behind the gradient attenuation plate and is used to change the polarization direction of the laser so that the polarization direction is along the x-axis direction; A first objective lens is disposed behind the first half-wave plate and is used to tightly focus the light beam emitted by the first laser so that the focus is located within the nonlinear crystal; A three-dimensional nano-translation stage, on which a nonlinear crystal is placed, is used to move the position of the nonlinear crystal so that the laser emitted by the first laser scribes from deep to shallow along the crystal axis direction of the nonlinear crystal, forming two groups of grating structures aligned along the y-axis direction; Wherein, the optical characterization module specifically includes: A second laser is used to emit laser light along the x-axis direction; A second half-wave plate is disposed behind the emission port of the second laser and is used to change the polarization direction of the laser light emitted by the second laser so that the polarization direction of the laser light is along the z-axis direction; A lens, disposed behind the second half-wave plate, for focusing the laser light emitted by the second laser so that the focal point is located in the nonlinear crystal laser processing area; The receiving screen is used to receive the diffraction spots passing through the laser processing area where the nonlinear crystal grating structure is located and the domain growth area where the nonlinear polarization grating is located, obtain the fundamental wave and the second harmonic signal, and verify the formation of the nonlinear grating structure.

2. The nonlinear grating processing system based on pyroelectric field induced polarization according to claim 1, characterized in that: The heat treatment module specifically includes: A vacuum temperature control platform, in which a nonlinear crystal with a grating structure is placed, is used to heat the nonlinear crystal to 180-240° C. at a first preset speed, then evacuate the vacuum temperature control platform to reach a preset vacuum degree, and then cool it to room temperature at a second preset speed, thereby forming a nonlinear polarization grating between two groups of grating structures of the nonlinear crystal; Polarized light microscopy system is used to perform real-time imaging of the ferroelectric domain change process between two sets of grating structures in nonlinear crystals.

3. The nonlinear grating processing system based on pyroelectric field induced polarization according to claim 2, characterized in that: The polarizing microscope system specifically comprises: An illumination light source, used for emitting white light toward the grating structure surface of the nonlinear crystal; A first polarizer is placed below the nonlinear crystal and above the illumination light source, and is used to convert the white light emitted by the illumination light source into linearly polarized light; A second objective lens is located above the nonlinear crystal and is used to diffuse the light passing through the processing area of ​​the nonlinear crystal; A second polarizer, the polarization direction of which is orthogonal to that of the first polarizer, is used to change the polarization direction of light; CCD for real-time imaging of the nonlinear crystal laser processing area.

4. A nonlinear grating processing method based on pyroelectric field induced polarization, characterized in that: The method is based on the nonlinear grating processing system according to claim 1, and the method comprises: Marking lines in a nonlinear crystal along a crystal axis direction, thereby forming two groups of aligned grating structures in the nonlinear crystal; specifically comprising: using a first laser to emit laser light along the crystal axis direction, and moving the position of the nonlinear crystal on a three-dimensional nano-translation stage, so that the laser light emitted by the first laser marks lines from deep to shallow along the crystal axis direction of the nonlinear crystal, thereby forming two groups of grating structures aligned along the y-axis direction; The nonlinear crystal is heated to 180-240°C, and then the environment where the nonlinear crystal is located is evacuated and cooled to room temperature, so that a pyroelectric field opposite to the spontaneous polarization direction is generated during the cooling process, thereby reversing the ferroelectric domains between the two groups of grating structures of the nonlinear crystal along the crystal axis direction to form a nonlinear polarization grating; The fundamental wave and second harmonic signals of the laser processing area where the grating structure of the nonlinear crystal is located and the domain growth area where the nonlinear polarization grating is located are collected to verify the formation of the nonlinear grating structure; specifically, the method comprises: using a second laser to emit laser along the x-axis direction, using a receiving screen to receive the diffraction spot passing through the laser processing area where the nonlinear crystal grating structure is located and the domain growth area where the nonlinear polarization grating is located, and obtaining the fundamental wave and second harmonic signals.

5. The nonlinear grating processing method based on pyroelectric field induced polarization according to claim 4, characterized in that: The nonlinear crystal is heated to 180-240° C., and then the environment where the nonlinear crystal is located is evacuated and cooled to room temperature, specifically comprising: The nonlinear crystal with a grating structure is heated to 180-240° C. at a first preset speed, and then evacuated to make the inside of the vacuum temperature control platform reach a preset vacuum degree, and then cooled to room temperature at a second preset speed.

6. The nonlinear grating processing method based on pyroelectric field induced polarization according to claim 5, characterized in that: The preset vacuum degree is 76 torr.

7. The nonlinear grating processing method based on pyroelectric field induced polarization according to claim 4, characterized in that: Heat the nonlinear crystal to 200-220°C.

8. The nonlinear grating processing method based on pyroelectric field induced polarization according to claim 4, characterized in that: The two groups of grating structures have a period of micrometer order and a spacing of micrometer order.

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