A light field control device that realizes dual-frequency and different diffraction functions simultaneously

Abstract

The invention discloses a light field control device for realizing dual-frequency different diffraction functions at the same time, characterized in that the device combines a laser processing technology and a vacuum quenching technology to process a lithium niobate crystal; the laser processing technology erases the nonlinear coefficient of the lithium niobate crystal and changes the refractive index at the same time; the vacuum quenching technology generates a pyroelectric field to polarize the ferroelectric domain of the lithium niobate crystal, changes the sign of the nonlinear coefficient, and does not affect the refractive index; the grating arrays processed by these two processes are perpendicular to each other and nested together, and based on the changes in the refractive index and the nonlinear coefficient, one-dimensional linear diffraction and two-dimensional nonlinear diffraction are respectively performed on the fundamental frequency light field; because the structures formed by the changes in the refractive index and the nonlinear coefficient are different, the fundamental frequency light and the doubled frequency light can respectively realize light field control with different functions.

Description

Technical Field

[0001] The present invention relates to the field of light field control technology, in particular to a light field control technology that simultaneously realizes dual-frequency different diffraction functions, and specifically to a light field control device that simultaneously realizes dual-frequency different diffraction functions. Background Art

[0002] Spatially structured light fields refer to light fields whose degrees of freedom, such as polarization, phase, and amplitude, are spatially distributed. Actively controlling the degrees of freedom of light in the spatial domain not only creates various new types of light fields, but also discovers a series of new phenomena and new effects, thereby developing new technologies and giving birth to new applications, making light field control one of the international frontier hotspots. After years of vigorous development, spatially structured light fields have made significant progress in generation, control, and application, especially in generation. Existing experimental techniques can create a rich variety of spatially structured light fields. Breakthroughs have also been made in nonlinear light field control. Metasurfaces and nonlinear photonic crystals can achieve light field control while performing nonlinear conversions. The birth of three-dimensional nonlinear photonic crystals has further improved the efficiency of nonlinear light field control.

[0003] Nonlinear crystals commonly used in the optical field include LiNbO 3 、LiTaO 3 and KTP crystals. In these crystals, there is a phenomenon of spontaneous polarization. The regions with the same polarization direction are called ferroelectric domains. Ferroelectric domains have two opposite polarization directions. The change of polarization direction is accompanied by the second-order nonlinear coefficient χ (2) The change of sign, the pyroelectric field generated by the applied electric field or the quenching process can reverse the direction of the ferroelectric domain. Femtosecond laser processing technology provides a flexible way to prepare three-dimensional nonlinear photonic crystals. It can control the ferroelectric domain at any position and erase part of the second-order nonlinear coefficient of the nonlinear crystal. At the same time, it will inevitably cause the refractive index to change, which has the advantages of low thermal effect and high resolution. Summary of the invention

[0004] In view of this, the present invention proposes a light field control device that can simultaneously realize dual-frequency different diffraction functions, and combines laser processing technology and vacuum quenching technology to process lithium niobate crystal, so that the fundamental frequency light and the doubled frequency light can respectively realize light field control with different functions.

[0005] The present invention solves the above problems by the following technical means:

[0006] In a first aspect, the present invention provides a light field control device that simultaneously realizes dual-frequency different diffraction functions, wherein the device combines a laser processing process and a vacuum quenching process to process a lithium niobate crystal;

[0007] Laser processing technology erases the nonlinear coefficient of lithium niobate crystal and changes the refractive index at the same time;

[0008] The vacuum quenching process generates a pyroelectric field to polarize the ferroelectric domains of the lithium niobate crystal, changing the sign of the nonlinear coefficient without affecting the refractive index.

[0009] The grating arrays processed by these two processes are perpendicular to each other and nested together, and based on the changes in refractive index and nonlinear coefficient, the fundamental frequency light field is subjected to one-dimensional linear diffraction and two-dimensional nonlinear diffraction respectively;

[0010] Since the structures formed by the change of refractive index and the change of nonlinear coefficient are different, the fundamental frequency light and the doubled frequency light can respectively realize light field regulation with different functions.

[0011] Preferably, the lines of the ferroelectric domain erasing region of the device are along the y direction, forming a grating array structure expressed by the formula:

[0012] f(x,y,z)=T[cos(G x x)]×T[cos(G y y)] (1)

[0013] The spatial frequency G x =2π / Λ x , G y =2π / Λ y , Λ x ,Λ y are the grating periods in the x and y directions in the rectangular coordinate system respectively; T is the binary function, for any value Z, it is expressed as:

[0014]

[0015] The laser processing technology erases the ferroelectric domain of the crystal, causing the change of the second-order nonlinear coefficient of the crystal Δχ (2) and the refractive index change Δn, the laser processed linear and nonlinear grating arrays are expressed as:

[0016] n(x,y,z)=n 0 -Δnf(x,y,z) (3)

[0017]

[0018] Where n 0 and Represents the original refractive index and nonlinear coefficient of lithium niobate crystal;

[0019] The lines of the ferroelectric domain polarization region of the device are along the z direction, forming a grating array structure expressed by the formula:

[0020]

[0021] Among them, the spatial frequency G z =2π / Λ z , Λ z is the grating period in the z direction in the rectangular coordinate system. The vacuum quenching process produces a pyroelectric field polarizing the crystal ferroelectric domain in the opposite direction to the spontaneous polarization of the crystal, changing the sign of the nonlinear coefficient without affecting the refractive index. The nonlinear grating array is expressed as:

[0022]

[0023] Therefore, the linear grating of the device is expressed by formula (3), which can linearly diffract the fundamental wave so that the fundamental wave is distributed in one dimension along the z direction; the nonlinear grating of the device is processed by laser processing and vacuum quenching process, which is expressed as:

[0024]

[0025] The nonlinear grating performs two-dimensional nonlinear diffraction on the fundamental wave along the y direction and the z direction. It can be seen that the light field control achieved by linear diffraction and nonlinear diffraction is not the same, and different light field control functions of the fundamental wave and the doubled frequency can be achieved.

[0026] Preferably, the laser processing technology is a femtosecond laser processing technology.

[0027] In a second aspect, the present invention provides a system for preparing a light field control device that simultaneously realizes dual-frequency and different diffraction functions, which is used to prepare the light field control device that simultaneously realizes dual-frequency and different diffraction functions, and includes a laser processing process subsystem and a vacuum quenching process subsystem;

[0028] The laser processing subsystem includes a first laser, a gradient attenuation plate, a first half-wave plate, a first objective lens, a lithium niobate crystal, a three-dimensional nano-translation stage and a computer;

[0029] The first laser emits laser light along the z direction of the optical axis, and the energy of the laser light is controlled by a gradient attenuation plate to compensate the energy in depth of the laser processing. After passing through the first half-wave plate, the polarization changes to be along the x direction. After passing through the first objective lens, the laser light is focused onto a magnesium-doped lithium niobate crystal. The lithium niobate crystal is placed on a three-dimensional nano-translation stage. The stroke of the three-dimensional nano-translation stage is controlled by a computer to process the laser light into a grating array along the z direction, and then into a grating array along the y direction.

[0030] The vacuum quenching process subsystem includes a vacuum temperature control platform, an illumination light source, a first polarizer, a second polarizer, a second objective lens and a CCD;

[0031] The laser processed lithium niobate crystal is placed on a vacuum temperature control platform, and the lithium niobate crystal is slowly heated to 180-220°C, then evacuated, and then quickly cooled to room temperature. During the cooling process, a pyroelectric field opposite to the spontaneous polarization direction is generated, which will induce the ferroelectric domain to reverse along the z direction from the position of the z-direction line processed by the laser. The illumination light source illuminates the crystal, and the orthogonal first polarizer and second polarizer are placed above and below the lithium niobate crystal, respectively, to ensure that only the laser processing area and the domain reversal area are illuminated, and then magnified by the second objective lens, and finally collected by the CCD to achieve real-time observation of the domain structure of the lithium niobate crystal.

[0032] Preferably, the first laser emits laser light with a wavelength of 800 nm, a pulse width of 34 fs and a repetition frequency of 1 kHz along the optical axis z direction.

[0033] Preferably, the laser processing subsystem further comprises an optical shutter, which is arranged between the first laser and the gradient attenuation plate and is used to control the opening and closing of the laser.

[0034] In a third aspect, the present invention provides a light field control system for realizing dual-frequency different diffraction functions at the same time, comprising the light field control device for realizing dual-frequency different diffraction functions at the same time, and also comprising a second laser, a second half-wave plate, a polarization beam splitter, a third half-wave plate and a lens;

[0035] The second laser emits laser along the x direction, controls the energy of the laser through the second half-wave plate and the polarization beam splitter, and then makes the polarization direction of the laser along the z direction through the third half-wave plate. Finally, it is focused by the lens and hits the light field control device that realizes the dual-frequency different diffraction function at the same time. The emitted fundamental frequency light field realizes one-dimensional diffraction; the fundamental wave is filtered out to observe the doubled frequency light field to realize two-dimensional diffraction.

[0036] Preferably, the second laser emits laser light with a wavelength of 800 nm, a pulse width of 140 fs, a repetition frequency of 80 MHz and a power of 400 mW along the x direction.

[0037] Compared with the prior art, the beneficial effects of the present invention include at least:

[0038] The present invention combines the laser processing technology and the vacuum quenching technology to process the lithium niobate crystal. The femtosecond laser erases the nonlinear coefficient of the lithium niobate crystal and changes the refractive index at the same time. The vacuum quenching process generates a pyroelectric field to polarize the ferroelectric domain of the lithium niobate crystal, changing the sign of the nonlinear coefficient without affecting the refractive index. The grating arrays processed by these two processes are perpendicular to each other and nested together. Based on the changes in the refractive index and the nonlinear coefficient, the fundamental frequency light field can be subjected to one-dimensional linear diffraction and two-dimensional nonlinear diffraction, respectively. Since the structures formed by the change in the refractive index and the change in the nonlinear coefficient are different, the fundamental frequency light and the doubled frequency light can respectively realize light field regulation with different functions. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0040] Figure 1 The following is a schematic diagram of the design of the optical field control device for realizing dual-frequency and different diffraction functions of the present invention, wherein (a) is a device structure diagram; (b) is a schematic diagram of the linear diffraction of fundamental frequency light; (c) is a schematic diagram of the nonlinear diffraction of fundamental frequency light;

[0041] Figure 2 The structure diagram of the preparation system of the optical field control device that realizes dual-frequency and different diffraction functions at the same time of the present invention, wherein (a) the optical path of femtosecond laser processing; (b) the morphology of the structure processed by femtosecond laser on the yoz surface; (c) the morphology of the structure processed by femtosecond laser on the yoz surface; (d) the optical path diagram of vacuum quenching; (e) the morphology of the structure on the yoz surface after vacuum quenching;

[0042] Figure 3 It is a structural diagram of the light field control system of the present invention that realizes dual-frequency and different diffraction functions at the same time (device characterization optical path);

[0043] Figure 4 This is the light spot diagram of the present invention, wherein (a) the device output light field; and (b) the frequency-doubled light field. DETAILED DESCRIPTION

[0044] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be pointed out that the described embodiments are only part of the embodiments of the present invention, not all of them. 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.

[0045] It should be understood that the orientation or positional relationship indicated by the terms "top", "bottom", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0046] The terms "first", "second", and "third" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first", "second", and "third" may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "a group" means two or more.

[0047] Example 1

[0048] like Figure 1 As shown, the present invention provides a light field control device that can simultaneously realize dual-frequency different diffraction functions. The device combines femtosecond laser processing technology and vacuum quenching technology to process lithium niobate crystals.

[0049] Femtosecond laser processing erases the nonlinear coefficients of lithium niobate crystals and changes the refractive index at the same time.

[0050] The vacuum quenching process generates a pyroelectric field to polarize the ferroelectric domains of the lithium niobate crystal, changing the sign of the nonlinear coefficient without affecting the refractive index.

[0051] The grating arrays processed by these two processes are perpendicular to each other and nested together. Based on the changes in the refractive index and the nonlinear coefficient, the fundamental frequency light field can be subjected to one-dimensional linear diffraction and two-dimensional nonlinear diffraction respectively.

[0052] Since the structures formed by the change of refractive index and the change of nonlinear coefficient are different, the fundamental frequency light and the doubled frequency light can respectively realize light field regulation with different functions.

[0053] This embodiment provides a light field control device that can realize dual-frequency and different diffraction functions at the same time. The device processing structure is as follows: Figure 1 (a) is shown. The light color is the ferroelectric domain erased area, and the lines are along the y direction, forming a grating array structure that can be expressed by the formula:

[0054] f(x,y,z)=T[cos(G x x)]×T[cos(G y y)] (1)

[0055] The spatial frequency G x =2π / Λ x , G y =2π / Λy , Λ x ,Λ y are the grating periods in the x and y directions in the rectangular coordinate system respectively; T is a binary function, which can be expressed as follows for any value of Z:

[0056]

[0057] Laser processing technology erases the ferroelectric domain of the crystal, causing a change in the second-order nonlinear coefficient of the crystal Δχ (2) and the refractive index change Δn, the linear and nonlinear grating arrays processed by femtosecond laser are expressed as:

[0058] n(x,y,z)=n 0 -Δnf(x,y,z) (3)

[0059]

[0060] Where n 0 and It represents the original refractive index and nonlinear coefficient of lithium niobate crystal; the dark color is the ferroelectric domain polarization area, and the lines are along the z direction, forming a grating array structure that can be expressed by the formula:

[0061]

[0062] Among them, the spatial frequency G z =2π / Λ z , Λ z They are the grating period in the z direction in the rectangular coordinate system. The vacuum quenching process produces a pyroelectric field that is opposite to the spontaneous polarization direction of the crystal to polarize the ferroelectric domain of the crystal, changing the sign of the nonlinear coefficient without affecting the refractive index. The nonlinear grating array can be expressed as:

[0063]

[0064] Therefore, the linear grating of the device can be expressed by formula (3), as follows: Figure 1 As shown in (b), the fundamental wave can be linearly diffracted so that the fundamental wave is distributed in one dimension along the z direction. The nonlinear grating of the device is processed by femtosecond laser and vacuum quenching process, which can be expressed as:

[0065]

[0066] The nonlinear grating performs two-dimensional nonlinear diffraction on the fundamental wave along the y and z directions, such as Figure 1 As shown in (c), it can be seen that the light field control achieved by linear diffraction and nonlinear diffraction is different, and different light field control functions of fundamental wave and double frequency can be achieved.

[0067] Example 2

[0068] The present invention provides a system for preparing a light field control device that simultaneously realizes dual-frequency different diffraction functions, which is used to prepare the light field control device that simultaneously realizes dual-frequency different diffraction functions, and includes a laser processing process subsystem and a vacuum quenching process subsystem.

[0069] The laser processing subsystem comprises a first laser, an optical shutter, a gradient attenuation plate, a first half-wave plate, a first objective lens, a lithium niobate crystal, a three-dimensional nano translation stage and a computer.

[0070] Laser erasure Figure 2 As shown in (a), the first laser emits a laser with a wavelength of 800nm, a pulse width of 34fs, and a repetition frequency of 1kHz along the z direction (optical axis direction). The opening and closing of the laser is controlled by an optical shutter, and the energy of the laser is controlled by a gradient attenuation plate to compensate for the energy in the depth of the laser processing. After passing through the first half-wave plate, the polarization is changed to be along the x direction. After the laser passes through the first objective lens with a numerical aperture of 0.75, it is focused onto a 5% magnesium-doped lithium niobate crystal. The lithium niobate crystal is placed on a three-dimensional nano-translation stage, and the computer (Labview software) is used to control the travel of the three-dimensional nano-translation stage, so that the laser processing can produce the following Figure 2 (a) Gray line structure in lithium niobate crystal. The line length along the z direction is 50 microns, with a period of Λ x is 12 microns, Λ y The length of the line along the y direction is 100 microns, and the period is Λ x is 12 microns, Λ z The actual laser processing structure on the yoz plane is as follows Figure 2 As shown in the dashed area in (b), on the xoy plane Figure 2 (c) is shown in the dashed area.

[0071] The vacuum quenching process subsystem includes a vacuum temperature control platform, an illumination light source, a first polarizer, a second polarizer, a second objective lens and a CCD.

[0072] Figure 2 The device shown in (d) is used to quench the laser-processed lithium niobate crystal under vacuum and observe its ferroelectric domain in real time. The laser-processed lithium niobate crystal is placed on a vacuum temperature control platform, slowly heated to 180-220°C, then evacuated, 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 induce the ferroelectric domain to reverse along the z direction from the position of the z-direction line processed by the femtosecond laser. Figure 2(d) The dark lines in the lithium niobate crystal are the polarization lines of the ferroelectric domain. The illumination light source illuminates the crystal, and the orthogonal first and second polarizers are placed above and below the lithium niobate crystal, respectively, to ensure that only the laser processing area and the domain inversion area can be illuminated, and then magnified by the second 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. The ferroelectric domains after vacuum quenching are shown in Figure 2. Figure 2 (e) The dotted area is shown.

[0073] Example 3

[0074] The present invention provides a light field control system for realizing dual-frequency different diffraction functions simultaneously, comprising the light field control device for realizing dual-frequency different diffraction functions simultaneously, and also comprising a second laser, a second half-wave plate, a polarization beam splitter, a third half-wave plate and a lens.

[0075] use Figure 3 The device is characterized by the optical path shown in FIG. 1 . The second laser emits a laser with a wavelength of 800 nm, a pulse width of 140 fs, a repetition frequency of 80 MHz, and a power of 400 mW along the x direction. The energy of the laser is controlled by the second half-wave plate and the polarization beam splitter. The polarization direction of the laser is then made along the z direction by the third half-wave plate. Finally, the laser is focused by a lens with a focal length of 75 mm and hits the optical field control device (processing structure) that realizes the dual-frequency different diffraction functions at the same time. The emitted light field is shown in FIG. Figure 4 As shown in (a), the fundamental frequency spot and the double frequency spot are superimposed together, where the red one is the fundamental frequency spot, which is diffracted in one dimension along the z direction. The fundamental wave is filtered out to observe the double frequency light field, as shown in Figure 4 As shown in (b), it presents two-dimensional diffraction in the yoz plane, and the period of the double frequency spot distribution is twice the period of the fundamental frequency spot.

[0076] The present invention combines the laser processing technology and the vacuum quenching technology to process the lithium niobate crystal. The femtosecond laser erases the nonlinear coefficient of the lithium niobate crystal and changes the refractive index at the same time. The vacuum quenching process generates a pyroelectric field to polarize the ferroelectric domain of the lithium niobate crystal, changing the sign of the nonlinear coefficient without affecting the refractive index. The grating arrays processed by these two processes are perpendicular to each other and nested together. Based on the changes in the refractive index and the nonlinear coefficient, the fundamental frequency light field can be subjected to one-dimensional linear diffraction and two-dimensional nonlinear diffraction, respectively. Since the structures formed by the change in the refractive index and the change in the nonlinear coefficient are different, the fundamental frequency light and the doubled frequency light can respectively realize light field regulation with different functions.

[0077] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A light field control device that realizes dual-frequency and different diffraction functions at the same time, characterized in that: The device combines laser processing technology and vacuum quenching technology to process lithium niobate crystals; Laser processing technology erases the nonlinear coefficient of lithium niobate crystal and changes the refractive index at the same time; The vacuum quenching process generates a pyroelectric field to polarize the ferroelectric domains of the lithium niobate crystal, changing the sign of the nonlinear coefficient without affecting the refractive index. The grating arrays processed by these two processes are perpendicular to each other and nested together. Based on the changes in refractive index and nonlinear coefficient, the fundamental frequency light is subjected to one-dimensional linear diffraction and two-dimensional nonlinear diffraction respectively. The linear grating performs linear diffraction on the fundamental frequency light, making the fundamental frequency light one-dimensionally distributed along the z direction, and the nonlinear grating performs two-dimensional nonlinear diffraction on the fundamental frequency light along the y direction and the z direction. Since the structures formed by the change of refractive index and the change of nonlinear coefficient are different, the fundamental frequency light and the doubled frequency light can respectively realize light field regulation with different functions.

2. The light field control device for realizing dual-frequency and different diffraction functions at the same time according to claim 1, characterized in that: The lines of the ferroelectric domain erasing region of the device are along the y direction, forming a grating array structure expressed by the formula: f(x,y,z)=T[cos(G x x)]×T[cos(G y y)] (1) The spatial frequency G x =2π / Λ x , G y =2π / Λ y , Λ x ,Λ y are the grating periods in the x and y directions in the rectangular coordinate system respectively; T is the binary function, for any value Z, it is expressed as: The laser processing technology erases the ferroelectric domain of the crystal, causing the change of the second-order nonlinear coefficient of the crystal Δχ (2) and the refractive index change Δn, the laser processed linear and nonlinear grating arrays are expressed as: n(x,y,z)=n0-Δnf(x,y,z) (3) where n0 and Represents the original refractive index and nonlinear coefficient of lithium niobate crystal; The lines of the ferroelectric domain polarization region of the device are along the z direction, forming a grating array structure expressed by the formula: Among them, the spatial frequency G z =2π / Λ z , Λ z is the grating period in the z direction in the rectangular coordinate system. The vacuum quenching process produces a pyroelectric field polarizing the crystal ferroelectric domain in the opposite direction to the spontaneous polarization of the crystal, changing the sign of the nonlinear coefficient without affecting the refractive index. The nonlinear grating array is expressed as: Therefore, the linear grating of the device is expressed by formula (3), which can linearly diffract the fundamental frequency light so that the fundamental frequency light is distributed in one dimension along the z direction; the nonlinear grating of the device is processed by laser processing and vacuum quenching process, which is expressed as: The nonlinear grating performs two-dimensional nonlinear diffraction on the fundamental frequency light along the y direction and the z direction. It can be seen that the light field control achieved by linear diffraction and nonlinear diffraction is not the same, and different light field control functions can be achieved for fundamental frequency light and double frequency light.

3. The light field control device for realizing dual-frequency and different diffraction functions at the same time according to claim 1, characterized in that: The laser processing technology is a femtosecond laser processing technology.

4. A system for preparing a light field control device that realizes dual-frequency and different diffraction functions at the same time, used for preparing a light field control device that realizes dual-frequency and different diffraction functions at the same time as claimed in any one of claims 1 to 3, characterized in that: Including laser processing subsystem and vacuum quenching subsystem; The laser processing subsystem includes a first laser, a gradient attenuation plate, a first half-wave plate, a first objective lens, a lithium niobate crystal, a three-dimensional nano-translation stage and a computer; The first laser emits laser light along the z direction of the optical axis, and the energy of the laser light is controlled by a gradient attenuation plate to compensate the energy in depth of the laser processing. After passing through the first half-wave plate, the polarization changes to be along the x direction. After passing through the first objective lens, the laser light is focused onto a magnesium-doped lithium niobate crystal. The lithium niobate crystal is placed on a three-dimensional nano-translation stage. The stroke of the three-dimensional nano-translation stage is controlled by a computer to process the laser light into a grating array along the z direction, and then into a grating array along the y direction. The vacuum quenching process subsystem includes a vacuum temperature control platform, an illumination light source, a first polarizer, a second polarizer, a second objective lens and a CCD; The laser processed lithium niobate crystal is placed on a vacuum temperature control platform, and the lithium niobate crystal is slowly heated to 180-220°C, then evacuated, and then quickly cooled to room temperature. During the cooling process, a pyroelectric field opposite to the spontaneous polarization direction is generated, which will induce the ferroelectric domain to reverse along the z direction from the position of the z-direction line processed by the laser. The illumination light source illuminates the crystal, and the orthogonal first polarizer and second polarizer are placed above and below the lithium niobate crystal, respectively, to ensure that only the laser processing area and the domain reversal area are illuminated, and then magnified by the second objective lens, and finally collected by the CCD to achieve real-time observation of the domain structure of the lithium niobate crystal.

5. The system for preparing a light field control device that realizes dual-frequency and different diffraction functions at the same time according to claim 4, characterized in that: The first laser emits laser light with a wavelength of 800 nm, a pulse width of 34 fs and a repetition frequency of 1 kHz along the optical axis z direction.

6. The system for preparing a light field control device that realizes dual-frequency and different diffraction functions at the same time according to claim 4, characterized in that: The laser processing subsystem further includes an optical shutter, which is arranged between the first laser and the gradient attenuation plate and is used to control the opening and closing of the laser.

7. A light field control system for realizing dual-frequency and different diffraction functions simultaneously, comprising a light field control device for realizing dual-frequency and different diffraction functions simultaneously as claimed in any one of claims 1 to 3, characterized in that: Also includes a second laser, a second half-wave plate, a polarization beam splitter, a third half-wave plate and a lens; The second laser emits laser along the x direction, controls the energy of the laser through the second half-wave plate and the polarization beam splitter, and then makes the polarization direction of the laser along the z direction through the third half-wave plate. Finally, it is focused by the lens and hits the light field control device that realizes the dual-frequency different diffraction function at the same time. The emitted fundamental frequency light realizes one-dimensional diffraction; the fundamental frequency light is filtered out and the doubled frequency light is observed to realize two-dimensional diffraction.

8. The light field control system for realizing dual-frequency and different diffraction functions simultaneously according to claim 7, characterized in that: The second laser emits laser light with a wavelength of 800 nm, a pulse width of 140 fs, a repetition frequency of 80 MHz, and a power of 400 mW along the x direction.

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