Nanopolarization system and polarization and depolarization methods in ferroelectric materials

Abstract

The application discloses a ferroelectric material internal nano polarization system and polarization and depolarization methods. The polarization system comprises a femtosecond laser, a half-wave plate, a polarization beam splitter, a 4f optical system, a light shutter, a dichroic mirror, a microscopic objective lens driven by a one-dimensional nano displacement stage, a sample stage driven by a three-dimensional nano displacement stage, an illumination module and an imaging module. The polarization and depolarization methods are realized based on the polarization system. The application has higher precision and can realize three-dimensional reconstruction.

Description

TECHNICAL FIELD

[0001] The present application relates to the polarization technology, and particularly to a nanometer polarization system inside ferroelectric material and polarization method and depolarization method. BACKGROUND

[0002] Nonlinear optics is an important branch of modern optics, and has a wide range of applications in the fields of information communication, information storage, imaging, sensing, etc. In nonlinear processes, such as frequency conversion processes, nonlinear optical materials are widely used. However, the inherent dispersion characteristics of the material greatly limit the conversion efficiency. Nonlinear photonic crystals with periodic second-order nonlinear coefficients can provide inverse reciprocal vectors to compensate for the wave vector mismatch in frequency conversion, and this matching method is also called quasi-phase matching. Nonlinear photonic crystals need to artificially regulate the ferroelectric domain orientation of the nonlinear crystal, so that the second-order nonlinear coefficient presents a periodic distribution.

[0003] The most commonly used method for preparing nonlinear photonic crystals is electrode polarization, which has good stability, high precision, and is almost suitable for all ferroelectric materials, so it has been widely used. Microscale domain structure can be obtained by ultraviolet exposure, and sub-micron scale domain structure can be obtained by electron beam exposure. Due to the limitation of the diffraction limit, theoretically, it is impossible to realize infinite small domain inversion. In addition, ultraviolet polarization, chemical diffusion, scanning probe polarization, electron beam polarization, crystal growth and other technologies have also been applied, but these methods can only prepare one-dimensional or two-dimensional nonlinear photonic crystals. The preparation of three-dimensional nanometer nonlinear photonic crystals still faces great challenges.

[0004] Femtosecond laser direct writing technology has become the best choice to overcome this difficulty because of its characteristics of point-by-point processing in transparent materials. Femtosecond laser direct writing technology refers to focusing laser pulses inside the material using a microscope objective to interact with the material, and then controlling the processing position and speed through a nanometer displacement stage to realize point-by-point processing of the material. Femtosecond laser direct writing technology can be divided into cold processing and hot processing according to its mechanism of interaction with matter. Generally speaking, low-repetition-rate femtosecond lasers have almost no heat accumulation during processing due to their long pulse interval, and are called cold processing. High-repetition-rate femtosecond lasers have a small pulse interval, and heat accumulation dominates, which is called hot processing. In recent years, femtosecond processing technology has been widely used in the field of optics, such as processing waveguides inside materials, processing phase plates on the surface of materials, and other micro-nano photonic devices with three-dimensional spatial structure. However, the existing femtosecond nanometer direct writing technology cannot be reconfigured and cannot break the diffraction limit, and the direct writing precision needs to be further improved. SUMMARY

[0005] The present application aims to solve the problems existing in the prior art, and provides a ferroelectric material internal nanometer polarization system and polarization method and depolarization method with higher precision and reconfigurability.

[0006] The ferroelectric material internal nanometer polarization system comprises a femtosecond laser, a half-wave plate, a polarization beam splitter, a 4f optical system, a light shutter, a dichroic mirror, a microscopic objective lens driven by a one-dimensional nanometer displacement table, a sample table driven by a three-dimensional nanometer displacement table, an illumination module and an imaging module, wherein the femtosecond laser, the half-wave plate, the polarization beam splitter, the 4f optical system, the light shutter and the dichroic mirror are sequentially arranged from front to back along the light path, the microscopic objective lens is located behind the reflection surface of the dichroic mirror, the sample table is located below the microscopic objective lens, the illumination module is located below the sample table, and the imaging module is located behind the transmission surface of the dichroic mirror.

[0007] The ferroelectric material internal nanometer polarization method is based on the above system, and the method specifically comprises the following steps.

[0008] The ferroelectric axis of the ferroelectric material is placed parallel to the surface of the sample table;

[0009] The incident light power of the femtosecond laser is adjusted to induce the formation of a micro-interface in the ferroelectric material;

[0010] The one-dimensional nanometer displacement table is adjusted so that the microscopic objective lens driven thereby focuses a light spot in the ferroelectric material and locks the position;

[0011] The single maximum polarization width w max obtained when the moving direction of the focused light spot of the microscopic objective lens is the +z surface pointing to the -z surface is obtained;

[0012] The single minimum polarization width w min obtained when the moving direction of the focused light spot of the microscopic objective lens is perpendicular to the ferroelectric axis of the ferroelectric material is obtained;

[0013] If the polarization width w of the required ferroelectric domain is: w min< w < w max , the following steps are performed: the incident light power of the femtosecond laser is adjusted so that the energy density of the focused light spot of the microscopic objective lens is lower than the damage threshold of the ferroelectric material, and the generated thermal electric field intensity is higher than the coercive field intensity, and the sample table is moved by the three-dimensional nanometer displacement table, so that the focused light spot of the microscopic objective lens moves L length along a specific direction starting from the micro-interface, to realize the nanometer polarization of the ferroelectric material, and obtain the ferroelectric domain with the polarization width w; wherein L is the target polarization length, and the specific direction is specifically an angle θ with the opposite direction of the spontaneous polarization direction of the ferroelectric body, and the relationship between θ and the target length L can be approximately described by the following formula:

[0014] Furthermore, the method also includes:

[0015] If the required polarization width of the ferroelectric domains is w < w min Then perform the following steps:

[0016] A. Adjust the incident light power of the femtosecond laser so that the energy density of the focused spot of the microscope objective is lower than the damage threshold of the ferroelectric material, and the generated thermoelectric field intensity is higher than the coercive field intensity. Move the sample stage using a three-dimensional nano-displacement stage, so that the focused spot of the microscope objective moves a length L from the micro-interface along the +z plane to the -z plane, thereby obtaining a polarization width of w within the ferroelectric material. max Ferroelectric domains;

[0017] B. Adjust the incident light power of the femtosecond laser so that the power density of the focused spot of the microscope objective is higher than the coercive field of the inverted domains but lower than the damage threshold of the ferroelectric material. Move the sample stage using a three-dimensional nano-displacement stage, causing the ferroelectric domains to move in a direction parallel to the sample stage plane and perpendicular to the ferroelectric axis. max -w, and then move the sample stage through a three-dimensional nano-displacement stage to make the focused spot move relative to the ferroelectric material along the -z plane to the +z plane for direct writing, thereby realizing partial depolarization of the ferroelectric domains and obtaining ferroelectric domains with polarization width w.

[0018] Furthermore, the method also includes:

[0019] If the required polarization width of the ferroelectric domains is w > w max Then perform the following steps:

[0020] A. Calculate the number of repetitions Indicates rounding up;

[0021] B. Adjust the incident light power of the femtosecond laser so that the energy density of the focused spot of the microscope objective is lower than the damage threshold of the ferroelectric material and the generated thermoelectric field strength is higher than the coercive field strength. Move the sample stage by a one-dimensional nano-displacement stage so that the focused spot of the microscope objective moves L length from the micro-interface to the -z plane for direct writing.

[0022] C. The sample stage is moved using a three-dimensional nano-displacement stage, causing the ferroelectric material to move in a direction parallel to the sample stage plane and perpendicular to the ferroelectric axis. max Then return to step B and repeat until the number of iterations reaches n-1, resulting in a polarization width of (n-1)w. max ferroelectric domains, proceed to step D;

[0023] D. moving the sample stage by the three-dimensional nano displacement stage, so that the ferroelectric material moves in the direction parallel to the sample stage plane and perpendicular to the ferroelectric axis direction w m = w-(n-1)w max And return to step B to obtain the ferroelectric domain with polarization width w.

[0024] Further, the method for obtaining the incident light power of the femtosecond laser for inducing the micro-interface in the ferroelectric material body is:

[0025] Focusing the focused spot of the microscope objective to the inside of the ferroelectric material, then gradually increasing the power until a black spot, which is the micro-interface formed by the micro-explosion, can be observed in the imaging module, at this time the energy density of the focused spot reaches the damage threshold of the ferroelectric body, and the incident light power of the femtosecond laser at this time is recorded.

[0026] Further, the method for obtaining the incident light power of the focused spot of the microscope objective, which is lower than the damage threshold of the ferroelectric material and generates a thermal electric field intensity higher than the coercive field intensity, is:

[0027] Focusing the focused spot of the microscope objective to the inside of the ferroelectric material, then gradually increasing the power until a black spot, which is the micro-interface formed by the micro-explosion, can be observed in the imaging module, and the incident light power of the femtosecond laser at this time is recorded as the incident light power of the focused spot of the microscope objective, which is lower than the damage threshold of the ferroelectric material;

[0028] Gradually reducing the power, using the focused spot generated by different incident light powers for direct writing, then observing the area directly written, if it is polarized, continue to reduce until it cannot be polarized, and the lowest incident light power for polarization is the incident light power generating a thermal electric field intensity higher than the coercive field intensity.

[0029] Further, the method for obtaining the incident light power of the focused spot of the microscope objective, which is higher than the coercive field of the reversed domain, is:

[0030] Gradually reducing the power with the incident light power of the micro-interface induction as the upper limit, using the focused spot generated by different incident light powers for depolarization direct writing of the ferroelectric domain, then observing the area directly written, if it is depolarized, continue to reduce until it cannot be depolarized, and the lowest incident light power for depolarization is the incident light power of the focused spot of the microscope objective, which is higher than the coercive field of the reversed domain.

[0031] The nano depolarization method in the ferroelectric material body of the application is based on the above-mentioned system, and the method specifically comprises:

[0032] Placing the already polarized ferroelectric domain on the sample stage;

[0033] The incident light power of the femtosecond laser is adjusted, so that the power density of the focusing spot of the microscope objective is higher than the coercive field of the reversed domain and lower than the damage threshold of the ferroelectric material, the sample stage is moved by the three-dimensional nanometer displacement stage, so that the focusing spot is located on the polarized ferroelectric domain, and then the sample stage is moved by the three-dimensional nanometer displacement stage, so that the focusing spot moves along the -z plane to the +z plane on the polarized ferroelectric domain, and the de-polarization of the ferroelectric domain is realized.

[0034] Beneficial effects: the present application can realize three-dimensional reconfigurable nanopoling in ferroelectric materials, regulate the second-order nonlinear coefficient of ferroelectric materials in three dimensions, and obtain nanodomain breaking through the diffraction limit, with higher precision. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 is a structural diagram of the ferroelectric material internal nanopoling system provided by the present application;

[0036] Figure 2 is a schematic diagram of the direct writing direction: a. the direct writing direction is along +z to -z, realizing polarization with a width of w max ; b. the direct writing direction is along -z to +z, realizing de-polarization; c. the direct writing direction is at a certain angle with the ferroelectric axis, and the projection on the ferroelectric axis is anti-parallel to the spontaneous polarization direction of the ferroelectric body, realizing polarization with a width of w min< w < w max ; d. continuously controlling the polarization width, realizing polarization with a width of w < w min . DETAILED DESCRIPTION

[0037] The present embodiment provides a ferroelectric material internal nanopoling system, as Figure 1As shown, it comprises a femtosecond laser 1, a half-wave plate 2, a polarization beam splitter 3, a 4f optical system (two coaxial convex lenses 4, 5), a light shutter 6, a dichroic mirror 7, a microscope objective 8 driven by a one-dimensional nanometer displacement stage 15, a sample stage 9 driven by a three-dimensional nanometer displacement stage 16, an illumination module (including a wide-spectrum white light source 10 and a collimator 11 located between the wide-spectrum white light source 10 and the sample stage 9), and an imaging module (including a mirror 12, a convex lens 13 and a camera 14 arranged in the light path from front to back). The femtosecond laser 1, the half-wave plate 2, the polarization beam splitter 3, the 4f optical system, the light shutter 6, the dichroic mirror 7 are arranged in the light path direction in turn from front to back, the microscope objective 8 is located behind the reflecting surface of the dichroic mirror 7, the sample stage 9 is located below the microscope objective 8, the illumination module is located below the sample stage 9, and the imaging module is located behind the transmission surface of the dichroic mirror 7. Among them, the femtosecond laser is a titanium sapphire MHz femtosecond laser, the selection of laser wavelength is affected by the absorption band of the ferroelectric material, it is difficult for the laser with wavelength in the absorption band to penetrate the material surface and enter the interior, therefore, a wavelength far from the absorption band is selected, and the absorption mode is changed from traditional single-photon absorption to multi-photon absorption; the beam expanding system is optimized to expand the light beam to the entrance aperture of the microscope objective; the mirror is selected to be a model with metal film coating and matched with the working wavelength, so as to minimize the pulse broadening caused by interface reflection.

[0038] The embodiment also provides a method for nanometer polarization inside a ferroelectric material, which is based on the nanometer polarization system and specifically includes the following steps:

[0039] S1, placing the ferroelectric axis of the ferroelectric material parallel to the surface of the sample stage.

[0040] S2, adjusting the incident light power of the femtosecond laser to induce the formation of micro interfaces in the ferroelectric material.

[0041] The method for obtaining the incident light power of the femtosecond laser for inducing the formation of micro interfaces in the ferroelectric material is as follows: focusing the focused spot of the microscope objective inside the ferroelectric material, then gradually increasing the power until a black spot can be observed in the imaging module, the black spot is a micro interface formed by micro explosion, at this time the energy density of the focused spot reaches the damage threshold of the ferroelectric body, and the incident light power of the femtosecond laser at this time is recorded. The micro interface is the starting point of direct writing, or it can also take the micro explosion point as the starting point and directly write in any direction, and the track of direct writing can also be used as a kind of micro interface.

[0042] S3, adjusting the one-dimensional nanometer displacement stage so that the microscope objective driven thereby focuses the light spot inside the ferroelectric material and locks the position.

[0043] S4, obtaining the single maximum polarization width w that can be obtained when the moving direction of the focused spot of the microscope objective is the +z direction pointing to the -z direction max .

[0044] S5, the minimum polarization width w of a single time can be obtained when the moving direction of the focused spot of the microscope objective is perpendicular to the ferroelectric axis of the ferroelectric material min .

[0045] S6, if the polarization width w of the required ferroelectric domain is: w min< w < w max , the following steps are performed: adjusting the incident light power of the femtosecond laser, so that the energy density of the focused spot of the microscope objective is lower than the damage threshold of the ferroelectric material, and the generated thermal electric field intensity is higher than the coercive field intensity, and moving the sample table through the three-dimensional nanometer displacement table, so that the focused spot of the microscope objective starts from the micro-interface and moves L length along a certain direction to perform direct writing, thereby realizing nanometer polarization of the ferroelectric material, and obtaining a ferroelectric domain with a polarization width of w; wherein L is the target polarization length, and the certain direction is specifically: the direction opposite to the spontaneous polarization direction of the ferroelectric body at an angle θ, and the relationship between θ and the target length L can be approximately described by the following formula: In the embodiment, the microscope objective is not moved during movement, and the displacement table is moved, so that the focused spot moves relative to the ferroelectric material.

[0046] The polarization principle is: because the processing wavelength is far away from the absorption band edge of the ferroelectric body, the interaction between light and matter is mainly nonlinear absorption of the material. Nonlinear absorption causes the local energy of the region inside the ferroelectric body affected by the focused light to rise, and a temperature field and a steep temperature gradient are formed near the focused spot. The polarization effect is caused by the joint action of the temperature field and the temperature gradient. First, the coercive field of the ferroelectric body above the critical temperature decreases with the increase of temperature, and the existence of the temperature field reduces the coercive field in the region where the ferroelectric body interacts with light, thereby reducing the polarization voltage required, and it is easier to be polarized than at room temperature. Second, the interaction between the focused spot and the ferroelectric body causes the center temperature to rise, and a temperature difference is formed between the center and the surrounding non-affected region. Due to the pyroelectricity of the ferroelectric material, a local electric field is generated, and the electric field is distributed in a sphere with the center of the light spot as the sphere center, and the electric field direction points to the sphere center along the radial direction. When the local electric field strength opposite to the spontaneous polarization direction of the ferroelectric body is greater than the coercive field strength, the ferroelectric body can be effectively polarized. As shown in Figure 2 , when the moving direction of the focused spot relative to the ferroelectric body is along the -z direction of the ferroelectric body, the effective action electric field coverage is the largest, and the polarization width obtained after direct writing is also the largest; when the moving direction of the focused spot relative to the ferroelectric body is perpendicular to the ferroelectric axis, the effective action electric field coverage is the smallest, and the polarization width obtained after direct writing is also the smallest. Therefore, when the moving direction of the focused spot relative to the ferroelectric body is between the two, the polarization width is also between the two. By changing the direct writing direction, the polarization width can be controlled in a single direct writing process. The required polarization width w is: w min< w < w maxAt this time, the moving direction needs to be at an angle θ with the direction of the spontaneous polarization of the ferroelectric, and the relationship between θ and the target length L can be approximately described by the following formula:

[0047] S7, if the polarization width w of the required ferroelectric domain is < w min , then the following steps are performed:

[0048] A, adjust the incident light power of the femtosecond laser so that the energy density of the focused spot of the microscope objective is lower than the damage threshold of the ferroelectric material, and the generated thermal electric field strength is higher than the coercive field strength, move the sample stage by the three-dimensional nanometer displacement stage, so that the focused spot of the microscope objective moves L length from the micro-interface as the starting point and points to the -z plane along the +z plane, and then directly writes, so that a ferroelectric domain with a polarization width of w max is obtained in the ferroelectric material;

[0049] B, adjust the incident light power of the femtosecond laser so that the power density of the focused spot of the microscope objective is higher than the coercive field of the reversed domain and lower than the damage threshold of the ferroelectric material, move the sample stage by the three-dimensional nanometer displacement stage, so that the ferroelectric domain moves w max -w in the direction parallel to the sample stage plane and perpendicular to the ferroelectric axis, and then move the sample stage by the three-dimensional nanometer displacement stage, so that the focused spot moves along the -z plane to the +z plane relative to the ferroelectric material, and then directly writes, so as to realize the partial depolarization of the ferroelectric domain, and obtain a ferroelectric domain with a polarization width of w.

[0050] Wherein, the method for obtaining the incident light power of the focused spot of the microscope objective, which has an energy density lower than the damage threshold of the ferroelectric material and a generated thermal electric field strength higher than the coercive field strength, is as follows: focus the focused spot of the microscope objective inside the ferroelectric material, then gradually increase the power until a black spot can be observed in the imaging module, the black spot is a micro-interface formed by micro-explosion, record the incident light power of the femtosecond laser at this time as the incident light power of the focused spot of the microscope objective which has an energy density lower than the damage threshold of the ferroelectric material; gradually reduce the power, use the focused spot generated by different incident light powers to directly write, then observe the area directly written, if it is polarized, continue to reduce until it cannot be polarized, and the lowest incident light power at the time of polarization is the incident light power of the generated thermal electric field strength higher than the coercive field strength.

[0051] S8, if the polarization width w of the required ferroelectric domain is > w max , then the following steps are performed:

[0052] A, calculate the number of repetitions , which means rounding up;

[0053] B. Adjusting the incident light power of the femtosecond laser, so that the energy density of the focused light spot of the microscope objective is lower than the damage threshold of the ferroelectric material, and the generated thermal electric field intensity is higher than the coercive field intensity, moving the sample table by the one-dimensional nanometer displacement table, so that the focused light spot of the microscope objective moves L length along the +z direction as the starting point of the micro-interface and points to the -z direction;

[0054] C. Moving the sample table by the three-dimensional nanometer displacement table, so that the ferroelectric material moves w max in the direction parallel to the sample table plane and perpendicular to the ferroelectric axis, and returning to perform step B until the number of times reaches n-1, obtaining a ferroelectric domain with a polarization width of (n-1)w max , and performing step D;

[0055] D. Moving the sample table by the three-dimensional nanometer displacement table, so that the ferroelectric material moves w m = w-(n-1)w max in the direction parallel to the sample table plane and perpendicular to the ferroelectric axis, and returning to perform step B to obtain a ferroelectric domain with a polarization width of w.

[0056] Wherein, the method for obtaining the incident light power of the focused light spot of the microscope objective which is higher than the coercive field of the reversed domain is: gradually reducing the power with the micro-interface induced incident light power as the upper limit, using the focused light spot generated by different incident light powers to depolarize and directly write the ferroelectric domain, and then observing the area directly written, if it is depolarized, continue to reduce, until it cannot be depolarized, the lowest incident light power when the depolarization is realized is the incident light power of the focused light spot of the microscope objective which is higher than the coercive field of the reversed domain.

[0057] The embodiment also provides a method for nanometer depolarization inside a ferroelectric material, which is based on the polarization system, and specifically includes the following steps:

[0058] Placing the already polarized ferroelectric domain on the sample table;

[0059] Adjusting the incident light power of the femtosecond laser, so that the power density of the focused light spot of the microscope objective is higher than the coercive field of the reversed domain and lower than the damage threshold of the ferroelectric material, moving the sample table by the three-dimensional nanometer displacement table, so that the focused light spot is located on the already polarized ferroelectric domain, and then moving the sample table by the three-dimensional nanometer displacement table, so that the focused light spot moves along the -z direction to the +z direction on the already polarized ferroelectric domain to directly write, thereby realizing the depolarization of the ferroelectric domain.

Claims

1. A method for nano-polarization within ferroelectric materials, characterized in that: This method is based on the internal nano-polarization system of ferroelectric materials. The internal nano-polarization system includes a femtosecond laser, a half-wave plate, a polarizing beam splitter, a 4f optical system, an optical shutter, a dichroic mirror, a microscope objective driven by a one-dimensional nano-displacement stage, a sample stage driven by a three-dimensional nano-displacement stage, an illumination module, and an imaging module. The femtosecond laser, half-wave plate, polarizing beam splitter, 4f optical system, optical shutter, and dichroic mirror are arranged sequentially from front to back along the optical path. The microscope objective is located behind the reflecting surface of the dichroic mirror, the sample stage is located below the microscope objective, the illumination module is located below the sample stage, and the imaging module is located behind the transmitting surface of the dichroic mirror. Specifically, the method includes: The ferroelectric axis of the ferroelectric material is placed parallel to the surface of the sample stage; Adjusting the incident light power of a femtosecond laser induces the formation of micro-interfaces within the ferroelectric material; Adjust the one-dimensional nanostage so that the microscope objective it drives can focus the light spot inside the ferroelectric material and lock its position. The maximum single polarization width w can be obtained when the focused spot of a microscope objective moves from the +z plane to the -z plane. max ; The minimum single polarization width w that can be obtained when the focusing spot of the microscope objective moves in a direction perpendicular to the ferroelectric axis of the ferroelectric material. min ; If the required polarization width w of the ferroelectric domains is: w min< w < w max Then, the following steps are performed: Adjust the incident light power of the femtosecond laser so that the energy density of the focused spot of the microscope objective is lower than the damage threshold of the ferroelectric material, and the generated thermoelectric field intensity is higher than the coercive field intensity. Move the sample stage using a three-dimensional nano-displacement stage, so that the focused spot of the microscope objective moves along a specific direction by a length L from the micro-interface to achieve nano-polarization of the ferroelectric material, obtaining ferroelectric domains with a polarization width of w; where L is the target polarization length, and the specific direction is specifically: at an angle θ opposite to the spontaneous polarization direction of the ferroelectric material. The relationship between θ and the target length L can be approximately described by the following formula:

2. The method for nano-polarization of ferroelectric materials according to claim 1, characterized in that: The method also includes: If the required polarization width of the ferroelectric domains is w < w min Then perform the following steps: A. Adjust the incident light power of the femtosecond laser so that the energy density of the focused spot of the microscope objective is lower than the damage threshold of the ferroelectric material, and the generated thermoelectric field intensity is higher than the coercive field intensity. Move the sample stage using a three-dimensional nano-displacement stage, so that the focused spot of the microscope objective moves a length L from the micro-interface along the +z plane to the -z plane, thereby obtaining a polarization width of w within the ferroelectric material. max Ferroelectric domains; B. Adjust the incident light power of the femtosecond laser so that the power density of the focused spot of the microscope objective is higher than the coercive field of the inverted domains but lower than the damage threshold of the ferroelectric material. Move the sample stage using a three-dimensional nano-displacement stage, causing the ferroelectric domains to move in a direction parallel to the sample stage plane and perpendicular to the ferroelectric axis. max -w, and then move the sample stage through a three-dimensional nano-displacement stage to make the focused spot move relative to the ferroelectric material along the -z plane to the +z plane for direct writing, thereby realizing partial depolarization of the ferroelectric domains and obtaining ferroelectric domains with polarization width w.

3. The method for nano-polarization of ferroelectric materials according to claim 1, characterized in that: The method also includes: If the required polarization width of the ferroelectric domains is w > w max Then perform the following steps: A. Calculate the number of repetitions Indicates rounding up; B. Adjust the incident light power of the femtosecond laser so that the energy density of the focused spot of the microscope objective is lower than the damage threshold of the ferroelectric material and the generated thermoelectric field strength is higher than the coercive field strength. Move the sample stage by a one-dimensional nano-displacement stage so that the focused spot of the microscope objective moves L length from the micro-interface to the -z plane for direct writing. C. The sample stage is moved using a three-dimensional nano-displacement stage, causing the ferroelectric material to move in a direction parallel to the sample stage plane and perpendicular to the ferroelectric axis. max Then return to step B and repeat until the number of iterations reaches n-1, resulting in a polarization width of (n-1)w. max ferroelectric domains, proceed to step D; D. The sample stage is moved using a three-dimensional nano-displacement stage, causing the ferroelectric material to move in a direction parallel to the sample stage plane and perpendicular to the ferroelectric axis. m =w-(n-1)w max Then return to step B to obtain ferroelectric domains with a polarization width of w.

4. The method for nano-polarization of ferroelectric materials according to claim 1, characterized in that: The method for obtaining the incident light power of a femtosecond laser that induces the formation of micro-interfaces within ferroelectric materials is as follows: The focusing spot of the microscope objective is focused onto the interior of the ferroelectric material, and then the power is gradually increased until a black spot can be observed in the imaging module. This black spot is the micro-interface formed by the micro-explosion. At this time, the energy density of the focusing spot reaches the damage threshold of the ferroelectric material, and the incident light power of the femtosecond laser is recorded.

5. The method for internal nano-polarization of ferroelectric materials according to claim 1, characterized in that: The method for obtaining incident light power where the energy density of the focused spot of the microscope objective is lower than the damage threshold of the ferroelectric material and the generated thermoelectric field strength is higher than the coercive field strength is as follows: The focusing spot of the microscope objective is focused on the interior of the ferroelectric material, and then the power is gradually increased until a black spot can be observed in the imaging module. This black spot is the micro-interface formed by the micro-explosion. The incident light power of the femtosecond laser at this time is recorded as the incident light power that makes the energy density of the focusing spot of the microscope objective lower than the damage threshold of the ferroelectric material. The power is gradually reduced, and the focused light spots generated by different incident light powers are directly written. Then the area that has been directly written is observed. If it is polarized, the power is reduced again until it can no longer be polarized. The minimum incident light power that achieves polarization is the incident light power at which the generated thermoelectric field intensity is higher than the coercive field intensity.

6. The method for nano-polarization of ferroelectric materials according to claim 2, characterized in that: The method for obtaining the incident light power that makes the power density of the focused spot of a microscope objective higher than that of the coercive field of the inverted domain is as follows: The power is gradually reduced from the upper limit of the incident light power induced by the micro-interface. The ferroelectric domains are depolarized and directly written using the focused light spots generated by different incident light powers. Then, the written area is observed. If it is depolarized, the power is reduced again until it cannot be depolarized. The minimum incident light power to achieve depolarization is when the power density of the focused light spot of the microscope objective is higher than the incident light power of the coercive field of the inverted domain.

7. A method for nano-depolarization inside ferroelectric materials, characterized in that: This method is based on the internal nano-polarization system of ferroelectric materials. The internal nano-polarization system includes a femtosecond laser, a half-wave plate, a polarizing beam splitter, a 4f optical system, an optical shutter, a dichroic mirror, a microscope objective driven by a one-dimensional nano-displacement stage, a sample stage driven by a three-dimensional nano-displacement stage, an illumination module, and an imaging module. The femtosecond laser, half-wave plate, polarizing beam splitter, 4f optical system, optical shutter, and dichroic mirror are arranged sequentially from front to back along the optical path. The microscope objective is located behind the reflecting surface of the dichroic mirror, the sample stage is located below the microscope objective, the illumination module is located below the sample stage, and the imaging module is located behind the transmitting surface of the dichroic mirror. Specifically, the method includes: The polarized ferroelectric domains are placed on the sample stage; The incident light power of the femtosecond laser is adjusted so that the power density of the focused spot of the microscope objective is higher than the coercive field of the inverted domain and lower than the damage threshold of the ferroelectric material. The sample stage is moved by a three-dimensional nano-displacement stage so that the focused spot is located on the polarized ferroelectric domain. The sample stage is then moved again by a three-dimensional nano-displacement stage so that the focused spot moves directly from the -z plane to the +z plane on the polarized ferroelectric domain, thereby achieving depolarization of the ferroelectric domain.

Images