Ferroelectric crystal with uniform domain structure, periodic polarization method and application

Abstract

The invention discloses a ferroelectric crystal with a uniform domain structure, a periodic polarization method and application, and relates to the technical field of nonlinear optical crystal materials and laser. The method comprises the following steps of: evaporating a layer of uniform metal electrode on the front surface of a ferroelectric crystal material, and evaporating a layer of uniform transparent electrode on the negative surface of the ferroelectric crystal material; spin-coating photoresist on the surface of the ferroelectric crystal material on which the electrode is evaporated, and sequentially photoetching, developing, baking, corroding and removing the photoresist to obtain a ferroelectric crystal material carrying a metal electrode pattern; exciting the polarization reverse direction of the ferroelectric crystal material carrying the metal electrode pattern through a reverse voltage or electron beam focusing method, and constructing domain nucleus sites; and performing periodic polarization on the obtained ferroelectric crystal material through an external electric field. According to the method, the high-quality large-light-passing-size periodically-poled ferroelectric crystal material can be rapidly prepared, and the application scene and field of the periodically-poled ferroelectric crystal material can be widened by increasing the aperture of the periodically-poled ferroelectric crystal.

Description

Technical Field

[0001] The invention relates to the fields of nonlinear optical crystal material technology and laser technology, and in particular to a ferroelectric crystal with a uniform domain structure, a periodic poling method and applications. Background Art

[0002] Quasi-phase matching (QPM) technology compensates for the phase mismatch of light waves caused by refractive index dispersion by periodically regulating the nonlinear polarizability of the crystal, thereby improving the efficiency of nonlinear optical frequency conversion. Periodic inversion ferroelectric crystals are important materials for nonlinear frequency doubling, sum frequency, difference frequency, and optical parametric oscillation applications, and are widely used in laser, aerospace, quantum communication, military and other technical fields.

[0003] At present, the existing technology for preparing periodically polarized ferroelectric materials is mainly to use the external electric field method to anneal and polarize the original ferroelectric crystal, cut and polish it into a wafer, and then plate a conductive electrode on the wafer using micro-nano processing lithography technology, and finally apply a voltage of a special waveform to achieve periodic reversal of the ferroelectric domain of the wafer. So far, the polarization method of thin-film (less than 1mm) ferroelectric crystals has become mature, but due to the limitation of the crystal's ability to resist light damage, in order to obtain higher-power mid-infrared lasers, nonlinear crystals with large apertures are required to meet the needs of scientific research, industry and national defense. However, due to the high coercive field of the crystal and the lateral expansion of the inversion domain caused by long-term pressure, it is difficult to achieve electric field periodic polarization of thick-sized ferroelectric crystal materials. Simply increasing the polarization voltage will cause significant lateral expansion of the domain structure, making it difficult to obtain a uniform domain structure. Summary of the invention

[0004] One of the purposes of the present invention is to provide a method for periodic poling of ferroelectric crystals with uniform domain structure, which breaks through the limitation of using external electric field polarization method to prepare thick-sized (1 to 10 mm) ferroelectric crystal materials by optimizing the process, realizes the rapid polarization of periodically polarized reversal domains of periodically reversed ferroelectric crystal materials, improves the quality of reversal domains, and expands the application scenarios and fields of periodically poled ferroelectric crystal materials.

[0005] In order to achieve the above-mentioned purpose, the present invention adopts the following technical scheme: a periodic poling method for a ferroelectric crystal with a uniform domain structure, which comprises the following steps in sequence: S1, selecting a ferroelectric crystal material with a thickness of 0.1μm to 10mm, vapor-depositing a uniform metal electrode on the front side of the ferroelectric crystal material, and vapor-depositing a uniform transparent electrode on the negative side of the ferroelectric crystal material.

[0006] S2, spin-coating photoresist on the surface of the ferroelectric crystal material with the evaporated electrode; sequentially performing photolithography, development, baking, etching and removing the photoresist on the surface of the ferroelectric crystal material with the spin-coated photoresist to obtain a ferroelectric crystal material carrying a metal electrode pattern.

[0007] S3. The polarization of the ferroelectric crystal material carrying the metal electrode pattern is stimulated in the opposite direction by reverse voltage or electron beam focusing to construct domain nucleus sites for polarization activation process.

[0008] S4, periodically polarizing the ferroelectric crystal material obtained in step S3 by applying an external electric field, and removing electrodes on both sides of the obtained ferroelectric crystal material, thereby obtaining a ferroelectric crystal with a uniform domain structure.

[0009] In the above-mentioned periodic poling method for a ferroelectric crystal with a uniform domain structure, in step S1, the ferroelectric crystal material is lithium niobate, lithium tantalate, potassium titanyl phosphate, rubidium titanyl phosphate or potassium titanyl arsenate, or a thin film of lithium niobate, lithium tantalate, potassium titanyl phosphate, rubidium titanyl phosphate or potassium titanyl arsenate.

[0010] In the above-mentioned periodic poling method for a ferroelectric crystal with a uniform domain structure, the ferroelectric crystal material is lithium niobate.

[0011] In the above-mentioned periodic poling method for a ferroelectric crystal with a uniform domain structure, in step S1, the metal electrode is an aluminum electrode, and the transparent electrode is an indium tin oxide electrode.

[0012] The above-mentioned periodic poling method of a ferroelectric crystal with a uniform domain structure, in step S2, baking at a temperature of 50-70°C for 10-30 minutes during photolithography, and baking at a temperature of 50-70°C for 20-40 minutes during development; phosphoric acid is used in the etching process, and the metal electrode not covered by the photoresist is removed by phosphoric acid etching, and the photoresist is removed by acetone.

[0013] The above-mentioned periodic poling method for a ferroelectric crystal with a uniform domain structure, wherein the periodic poling is specifically 28 μm.

[0014] Another object of the present invention is to provide the above-mentioned ferroelectric crystal with uniform domain structure, which is prepared by the periodic poling method of the ferroelectric crystal with uniform domain structure.

[0015] In the above-mentioned ferroelectric crystal with uniform domain structure, the ferroelectric domains are arranged and distributed in a regular strip or pattern shape.

[0016] Another object of the present invention is to provide an application of the above-mentioned ferroelectric crystal with uniform domain structure in a nonlinear frequency conversion crystal device.

[0017] Compared with the prior art, the present invention brings the following beneficial technical effects: (1) The present invention proposes a method for periodic poling of a ferroelectric crystal with a uniform domain structure, which excites the polarization direction of a ferroelectric crystal material carrying a metal electrode pattern by reverse voltage or electron beam focusing to construct domain nucleus sites for polarization activation, and then controls the domain structure of the ferroelectric crystal material in the target polarization direction by applying an external electric field, thereby achieving rapid polarization and obtaining a periodically poled ferroelectric crystal with a uniform domain structure.

[0018] (2) The present invention can rapidly prepare high-quality, large-transmittance periodically poled ferroelectric crystal materials. The increase in the aperture of the periodically poled ferroelectric crystal can broaden the application scenarios and fields of the periodically poled ferroelectric crystal materials.

[0019] (3) The method of the present invention is particularly suitable for thick-sized (0.1 μm to 10 mm) ferroelectric crystal materials, overcoming the technical defect in the prior art that thick-sized ferroelectric crystal materials are difficult to achieve electric field periodic polarization. The present invention can adjust the direction and polarization period of the domain structure according to actual needs, has the ability to stably control the domain structure in non-target directions and obtain periodically polarized ferroelectric crystals, and can achieve a high-efficiency nonlinear frequency conversion process. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic diagram of reverse domain core excitation of a ferroelectric crystal material according to Example 1 of the present invention.

[0021] Figure 2 It is a domain core structure generated by activation through reverse voltage or electron beam focusing method.

[0022] Figure 3 Schematic diagram of the normal polarization process.

[0023] Figure 4 Schematic diagram of the polarization process after activation of the reverse domain core. DETAILED DESCRIPTION

[0024] The present invention proposes a ferroelectric crystal with a uniform domain structure, a periodic poling method and an application thereof. In order to make the advantages and technical solutions of the present invention clearer and more specific, the present invention is further described below in conjunction with specific embodiments.

[0025] The main technical concept of the present invention is: on the basis of the original polarization electric field, auxiliary external field polarization is used to prepare periodically polarized ferroelectric crystals, wherein the external field acts to construct ferroelectric domain cores that can play an activating role. The ferroelectric crystal is cut along a certain axial direction, a periodic electrode is plated on the front side of the ferroelectric crystal in a certain axial direction, a conductive layer is plated on the negative side in the axial direction, and a voltage is applied to the front side in the axial direction to form the original polarization electric field, and the negative side in the axial direction is grounded, so that the ferroelectric domain under the periodic electrode is reversed, and an external field is applied in other axial directions of the ferroelectric crystal to generate activated polarized ferroelectric domain cores. In this article, the external field preferably adopts reverse voltage or electron beam focusing method.

[0026] The domains in this article can be arranged and distributed in a regular strip or patterned shape, depending on the shape of the designed polarization electrode. The ferroelectric crystal material in this article is lithium niobate, lithium tantalate, potassium titanyl phosphate, rubidium titanyl phosphate or potassium titanyl arsenate, or a thin film thereof.

[0027] Attached Figure 1 The +z plane is the positive side of the ferroelectric crystal material, and the -z plane is the negative side of the ferroelectric crystal material.

[0028] The present invention will be further described below in conjunction with specific embodiments.

[0029] Embodiment 1: The ferroelectric crystal material in this embodiment is lithium niobate.

[0030] A periodic poling method for a lithium niobate crystal with a uniform domain structure comprises the following steps in sequence: S1, selecting a lithium niobate crystal material with a thickness of 100 μm, the light transmission direction of the lithium niobate crystal is the x direction, the polarization period is 28 μm, and designing a 28 μm period electrode mask.

[0031] A uniform aluminum electrode is evaporated on the front side of the lithium niobate crystal material, and a uniform indium tin oxide electrode is evaporated on the negative side of the lithium niobate crystal material.

[0032] S2. Spin-coat photoresist on the surface of the lithium niobate crystal material of the vapor-deposited electrode. The surface of the lithium niobate crystal material with the spin-coated photoresist is sequentially subjected to photolithography, development, baking, etching and removal of the photoresist to obtain a lithium niobate crystal material carrying a metal electrode pattern; during photolithography, the material is baked at a temperature of 60°C for 20 minutes, and during development, the material is baked at a temperature of 60°C for 30 minutes; phosphoric acid is used in the etching process to remove the metal electrode not covered by the photoresist by phosphoric acid etching, and the photoresist is removed by acetone.

[0033] S3, the reverse polarization direction of the lithium niobate crystal material carrying the metal electrode pattern is stimulated by reverse voltage to construct domain nucleus sites, which are used for polarization activation process. Figure 1As shown in the figure, under the real-time monitoring device, domain core structures are seen on the surface of lithium niobate crystals and are stably controlled. Figure 2 shown.

[0034] S4, periodically polarizing the lithium niobate crystal material obtained in step S3 by applying an external electric field, and removing the electrodes on both sides of the obtained lithium niobate crystal material, so as to obtain a lithium niobate crystal with a uniform domain structure, such as Figure 4 shown.

[0035] Embodiment 2: The ferroelectric crystal material in this embodiment is lithium tantalate.

[0036] A periodic poling method for a lithium tantalate crystal with a uniform domain structure comprises the following steps in sequence: S1, selecting a lithium tantalate crystal material with a thickness of 10 mm, the light transmission direction of the lithium tantalate crystal is the x direction, the polarization period is 28 μm, and designing a 28 μm period electrode mask.

[0037] A uniform aluminum electrode is evaporated on the front side of the lithium tantalate crystal material, and a uniform indium tin oxide electrode is evaporated on the negative side of the lithium tantalate crystal material.

[0038] S2. Spin-coat photoresist on the surface of lithium tantalate crystal material of the evaporated electrode. The surface of lithium tantalate crystal material with spin-coated photoresist is sequentially subjected to photolithography, development, baking, etching and removal of photoresist to obtain lithium tantalate crystal material carrying metal electrode pattern; during photolithography, the temperature is 50°C for 10 minutes, and during development, the temperature is 50°C for 20 minutes; phosphoric acid is used in the etching process to remove the metal electrode not covered by the photoresist by phosphoric acid etching, and the photoresist is removed by acetone.

[0039] S3. The reverse polarization direction of the lithium tantalate crystal material carrying the metal electrode pattern is stimulated by reverse voltage to construct domain nucleation sites for polarization activation process.

[0040] S4, periodically polarizing the lithium tantalate crystal material obtained in step S3 by applying an external electric field, and removing the electrodes on both sides of the obtained lithium tantalate crystal material, so as to obtain a lithium tantalate crystal with a uniform domain structure.

[0041] Embodiment 3: The ferroelectric crystal material in this embodiment is potassium titanyl phosphate.

[0042] A periodic poling method for potassium titanyl phosphate crystals with uniform domain structure comprises the following steps in sequence: S1, selecting a potassium titanyl phosphate crystal material with a thickness of 5 mm, the light transmission direction of the potassium titanyl phosphate crystal is the x direction, the polarization period is 28 μm, and designing a 28 μm period electrode mask.

[0043] A uniform aluminum electrode is evaporated on the front side of the potassium titanyl phosphate crystal material, and a uniform indium tin oxide electrode is evaporated on the negative side of the potassium titanyl phosphate crystal material.

[0044] S2. Spin-coat photoresist on the surface of potassium titanyl phosphate crystal material of the vapor-deposited electrode. The surface of the potassium titanyl phosphate crystal material on which the photoresist is spun is sequentially subjected to photolithography, development, baking, etching and removal of the photoresist to obtain a potassium titanyl phosphate crystal material carrying a metal electrode pattern; during photolithography, the material is baked at 70°C for 30 minutes, and during development, the material is baked at 70°C for 40 minutes; phosphoric acid is used in the etching process to remove the metal electrode not covered by the photoresist by phosphoric acid etching, and the photoresist is removed by acetone.

[0045] S3. The polarization of the potassium titanium phosphate oxide crystal material carrying the metal electrode pattern is excited in the opposite direction by electron beam focusing to construct domain nucleus sites for polarization activation process.

[0046] S4, periodically polarizing the potassium titanyl phosphate crystal material obtained in step S3 by applying an external electric field, and removing the electrodes on both sides of the obtained potassium titanyl phosphate crystal material, so as to obtain potassium titanyl phosphate crystals with a uniform domain structure.

[0047] The ferroelectric crystals prepared in the above-mentioned embodiments 1 to 3 can be used as a one-dimensional quasi-phase-matched optical parametric crystal device for light sources with wavelengths ranging from 1.064 μm to 5 μm.

[0048] Comparative Example 1: The ferroelectric crystal material in this comparative example is lithium niobate.

[0049] A polarization method for lithium niobate crystals comprises the following steps in sequence: S1, selecting a lithium niobate crystal material with a thickness of 100 μm, the light transmission direction of the lithium niobate crystal is the x direction, the polarization period is 28 μm, and designing a 28 μm period electrode mask.

[0050] A uniform aluminum electrode is evaporated on the front side of the lithium niobate crystal material, and a uniform indium tin oxide electrode is evaporated on the negative side of the lithium niobate crystal material.

[0051] S2. Spin-coat photoresist on the surface of the lithium niobate crystal material of the vapor-deposited electrode. The surface of the lithium niobate crystal material with the spin-coated photoresist is sequentially subjected to photolithography, development, baking, etching and removal of the photoresist to obtain a lithium niobate crystal material carrying a metal electrode pattern; during photolithography, the material is baked at a temperature of 60°C for 20 minutes, and during development, the material is baked at a temperature of 60°C for 30 minutes; phosphoric acid is used in the etching process to remove the metal electrode not covered by the photoresist by phosphoric acid etching, and the photoresist is removed by acetone.

[0052] S3, polarizing the lithium niobate crystal material obtained in step S2 by applying an external electric field, and removing the electrodes on both sides of the obtained lithium niobate crystal material, so as to obtain a lithium niobate crystal, such as Figure 3 shown.

[0053] Parts not described in the present invention can be implemented by referring to the existing technology.

[0054] Those skilled in the art should recognize that the above embodiments are only used to illustrate the present application and are not intended to be limiting of the present application. As long as they are within the spirit and scope of the present application, appropriate changes and modifications to the above embodiments are within the scope of protection of the claims of the present application.

Claims

1. A method for periodic poling of a ferroelectric crystal with a uniform domain structure, characterized in that: The following steps are included in sequence: S1. Select a ferroelectric crystal material with a thickness of 0.1 μm to 10 mm, evaporate a uniform metal electrode on the front side of the ferroelectric crystal material, and evaporate a uniform transparent electrode on the negative side of the ferroelectric crystal material; S2, spin coating photoresist on the surface of the ferroelectric crystal material of the evaporated electrode; The surface of the ferroelectric crystal material on which the photoresist is spin-coated is subjected to photolithography, development, baking, etching and removal of the photoresist in sequence to obtain a ferroelectric crystal material carrying a metal electrode pattern; S3, exciting the polarization reverse direction of the ferroelectric crystal material carrying the metal electrode pattern by reverse voltage or electron beam focusing method, constructing domain nucleus sites, and using them for polarization activation process; S4, periodically polarizing the ferroelectric crystal material obtained in step S3 by applying an external electric field, and removing electrodes on both sides of the obtained ferroelectric crystal material, thereby obtaining a ferroelectric crystal with a uniform domain structure.

2. The method for periodic poling of a ferroelectric crystal with a uniform domain structure according to claim 1, characterized in that: In step S1, the ferroelectric crystal material is lithium niobate, lithium tantalate, potassium titanyl phosphate, rubidium titanyl phosphate or potassium titanyl arsenate, or a thin film of lithium niobate, lithium tantalate, potassium titanyl phosphate, rubidium titanyl phosphate or potassium titanyl arsenate.

3. The method for periodic poling of a ferroelectric crystal with a uniform domain structure according to claim 2, characterized in that: The ferroelectric crystal material is lithium niobate.

4. The method for periodic poling of a ferroelectric crystal with a uniform domain structure according to claim 1, characterized in that: In step S1, the metal electrode is an aluminum electrode, and the transparent electrode is an indium tin oxide electrode.

5. The method for periodic poling of a ferroelectric crystal with a uniform domain structure according to claim 1, characterized in that: In step S2, during photolithography, the photoresist is baked at a temperature of 50-70° C. for 10-30 minutes, and during development, the photoresist is baked at a temperature of 50-70° C. for 20-40 minutes. Phosphoric acid is used in the etching process to remove the metal electrode not covered by the photoresist by phosphoric acid etching, and the photoresist is removed by acetone.

6. The method for periodic poling of a ferroelectric crystal with a uniform domain structure according to claim 1, characterized in that: The periodic poling is specifically 28 μm.

7. A ferroelectric crystal with a uniform domain structure, characterized in that: The crystal is prepared by the periodic poling method of a ferroelectric crystal with a uniform domain structure according to any one of claims 1 to 6.

8. The ferroelectric crystal with uniform domain structure according to claim 7, characterized in that: The arrangement and distribution of the ferroelectric domains in the ferroelectric crystal is in the shape of regular strips or patterns.

9. Application of a ferroelectric crystal with a uniform domain structure according to claim 7 in a nonlinear frequency conversion crystal device.

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