Wet-assisted femtosecond laser processing of optically anisotropic nanopores in crystals

Abstract

The present invention discloses a wet-assisted femtosecond laser processing method for nanopores in optically anisotropic crystals. A thicker optically isotropic crystal is placed on the optically anisotropic crystal of the target workpiece through optical contact as a spherical aberration enhancement auxiliary. The femtosecond laser is transmitted through the spherical aberration enhancement auxiliary and then incident and focused into the target workpiece to produce a self-focusing wiredrawing effect, and the induced material is locally modified into a nanowiredrawing induction area; then, wet etching is performed with a specific acidic solution, and the nanowiredrawing induction area is etched to form a nanopore with controllable pore size and a high aspect ratio. The present invention can induce processing of the three-dimensional space inside any optically anisotropic crystal, and can also adjust and prepare nanopore structures with a high aspect ratio, overcoming the disadvantage that traditional methods can only process nanopore structures with a low aspect ratio on the surface of the material, and preparing smaller, uniform, and controllable nanopore structures, with the characteristics of efficient, stable, and low-cost three-dimensional space controllable nanoprocessing.

Description

Technical Field

[0001] The present invention relates to a femtosecond laser processing method in the field of laser processing, and in particular to a method for processing "nanopores with controllable aperture and high aspect ratio" in optically anisotropic crystals using a wet-assisted femtosecond laser. Background Art

[0002] As we all know, the development of silicon-based microelectronic chips is gradually approaching the limits predicted by Moore's Law—that is, around the 2020s, the size of a single transistor should be comparable to the diameter of an atom. To usher in the post-Moore era, photonic chips offer unique advantages: high integration, low optical signal crosstalk, low energy consumption, and radiation resistance. The successful research of nanophotonic devices (including nanolasers, photon sensors, optical amplifiers, optical modulators, optical switches, etc.) is the cornerstone of the ultimate realization of all-optical photonic integrated chips. As we all know, nanophotonic devices are primarily based on the controllable processing of fine nanostructures. Traditionally, fine nanostructures have relied on methods such as UV lithography, EBL, FIB, and RIE to fabricate them. There are many problems: 1) Only two-dimensional nanostructures can be processed on the surface of the material, and the required nanostructures cannot be processed in the three-dimensional space inside the material; 2) Only nanostructures with a relatively low aspect ratio can be processed, which limits the development of nanophotonic devices. For example, nanostructures with a high aspect ratio have always been pursued in the preparation of large-area, achromatic superlenses; 3) The processing technology is complex, expensive, time-consuming, and the processing stability deteriorates over time; 4) It is difficult to process nanostructures approaching 10nm.

[0003] The existing femtosecond laser direct writing technology has achieved the processing of different nanophotonic structures in many hard and transparent materials, including self-assembled nanogratings, distributed Bragg gratings, nanostructures prepared by beam shaping, nanoholes, etc.

[0004] However, there are still many fundamental problems with femtosecond laser direct writing:

[0005] 1) It is difficult to directly write arbitrary 3D shape-controllable, sub-wavelength-resolved (λ / 10), low-loss nanophotonic structures;

[0006] 2) It is difficult to induce a large refractive index difference (Δn>0.5), which hinders its development in nanophotonic devices;

[0007] 3) Femtosecond laser direct writing easily causes longitudinal depth elongation, which is not conducive to the processing of nanostructures with uniform and controllable dimensions in any direction;

[0008] 4) Femtosecond laser uses beam shaping to process nanostructures, which can easily lead to serious sidelobe effects, resulting in unevenness around the nanostructure and even serious defects such as microcracks.

[0009] Therefore, among the many hard and transparent materials, transparent crystals are the most representative, with broad application prospects in high-power lasers and extreme working environments. Crystals can be divided into optically isotropic crystals and optically anisotropic crystals, and the difference is essentially based on the presence or absence of birefringence.

[0010] Unlike optically isotropic crystals, when a femtosecond laser beam propagates in an optically anisotropic crystal, due to the asymmetry of the crystal's optical axis, the femtosecond laser beam is easily deflected and bifurcated after passing through the optically anisotropic crystal, which in turn deteriorates the uniformity of the femtosecond laser light field. Ultimately, the interaction between the femtosecond laser and the optically anisotropic crystal is complex and changeable, making it difficult to process uniform and controllable nanophotonic structures in the optically anisotropic crystal.

[0011] Therefore, the existing technology lacks a femtosecond laser processing method for achieving uniform and controllable nanophotonic structure processing and preparation in optically anisotropic crystals. Summary of the Invention

[0012] In response to the problems in the above-mentioned background technology, the present invention utilizes femtosecond laser direct writing technology combined with the high efficiency, high precision and strong flexibility of femtosecond laser processing, and proposes a wet-assisted femtosecond laser nano-processing method for preparing "nanopores with controllable aperture and high aspect ratio" in optically anisotropic crystals. It is an efficient, stable and low-cost three-dimensional space controllable processing method.

[0013] The method of the present invention utilizes a femtosecond laser to generate a self-focusing nanowire drawing effect through spherical aberration enhancement in a thicker optically isotropic crystal. The generated femtosecond laser nanowires propagate and focus into a thinner optically anisotropic crystal. The femtosecond laser parameters are regulated to locally induce, draw, and modify the optically anisotropic crystal material. Finally, with the aid of an acidic solution, the modified area of ​​the optically anisotropic crystal material induced by the femtosecond laser can be selectively wet-etched to prepare a "nanopore with controllable aperture and high aspect ratio" structure.

[0014] The technical solution adopted in the present invention is:

[0015] The method of the present invention is directed to a piece of optically anisotropic crystal to be processed as a target object, and specifically includes the following steps:

[0016] First, another optically isotropic crystal that is thicker than the target workpiece and has an adjustable thickness is placed in optical contact on one side of the target workpiece as a spherical aberration enhancement auxiliary to form an optical contact stack. A femtosecond laser is applied from the spherical aberration enhancement auxiliary to the target workpiece, passes through the spherical aberration enhancement auxiliary, and then is incident and focused into the interior of the target workpiece. Based on the spherical aberration enhancement effect of the femtosecond laser, the self-focusing wiredrawing effect of the femtosecond laser is enhanced, and the self-focusing wiredrawing inducing material is locally modified inside the optically anisotropic crystal of the target workpiece to form a nanowiredrawing inducing region; the diameter of the nanowiredrawing inducing region is on the nanometer scale, and the direction of the filaments is consistent with the direction of the femtosecond laser incident on the anisotropic crystal, and is perpendicular to the surface of the optically anisotropic crystal / optically isotropic crystal.

[0017] The target object is then wet-etched with a specific acidic solution, so that the nanowire drawing induction area is etched to form nanopores with controllable pore size and high aspect ratio.

[0018] The high aspect ratio mentioned in the present invention refers to a aspect ratio greater than 4000:1 or even higher, which can be achieved by properly adjusting parameters such as the thickness of the spherical aberration enhancement auxiliary, the working distance of the focusing objective lens, and the power of the femtosecond laser.

[0019] Specifically, a thin optically anisotropic crystal is used as the target workpiece, while a relatively thicker optically isotropic crystal is stacked in optical contact on the upper surface of the target workpiece as an auxiliary material for spherical aberration enhancement. The two crystals maintain optical contact, and when the femtosecond laser beam passes through the thicker optically isotropic crystal, it produces significant spherical aberration enhancement, prompting the femtosecond laser to form a uniform localized nanofilament region as an induction region during the self-focusing process. The crystal material in the localized nanofilament region is modified to form a nanowire induction region.

[0020] The optically anisotropic crystal of the target object is made of sapphire, lithium niobate crystal, etc., and is characterized by being relatively thin and having a relatively thick optically isotropic crystal stacked in optical contact on its upper surface for enhancing spherical aberration; the type of the optically anisotropic crystal, the sample thickness, and the method of optically contacting and stacking with the optically anisotropic crystal are arbitrarily adjustable;

[0021] The optically isotropic crystal material of the spherical aberration enhancement auxiliary is YAG, LuAG, diamond crystal, etc. Its crystal axis is optically isotropic and has no birefringence effect. The laser propagation in this type of crystal will not be affected by the crystal axis, and the light beam always maintains uniform and directional propagation.

[0022] The relative thickness of the spherical aberration enhancement auxiliary compared to the target workpiece is greater than the range of 1-10 mm.

[0023] In specific implementation, femtosecond lasers use different output wavelengths such as 355, 532, 800, and 1030 nm, different pulse widths (50 fs–10 ps), different repetition frequencies (1 Hz–100 kHz), and pulse train output modes with high repetition rates, different powers, different polarizations (including linear polarization and circular polarization), and different numbers of exposure pulses.

[0024] Focusing is achieved through aspherical focusing objectives with different magnifications and numerical apertures NA.

[0025] The femtosecond laser is focused on any relative position inside the optically anisotropic crystal as the target processing object through the focusing objective of the aspheric mirror for exposure, so that the microscopic atomic arrangement and looseness of the local space material of the crystal after exposure are changed, thereby forming a slender nano-wire drawing induction area.

[0026] The aperture of the nanopore is controlled by parameters such as the output wavelength, pulse width, repetition rate, power, and exposure pulse number of the femtosecond laser, and the aperture range is 30-300nm.

[0027] The depth-to-diameter ratio of the nanopore is controlled by parameters such as the refractive index of the optically anisotropic crystal as the target processing object, the thickness of the optically isotropic crystal as the auxiliary object, the working distance of the focusing objective lens, and the power of the femtosecond laser. The depth-to-diameter ratio is as high as 4000:1.

[0028] The "nanopore with controllable aperture and high aspect ratio" can achieve adjustable aperture of the nanopore in the range of 30-300nm by regulating parameters such as the output wavelength, pulse width, repetition rate, power, and number of exposure pulses of the femtosecond laser. In addition, by selecting target processing materials of optically anisotropic crystals with different refractive indices and regulating parameters such as the thickness of the optically contact stacked optically isotropic crystal material used as a spherical aberration enhancement auxiliary, the working distance of the focusing mirror, and the power of the femtosecond laser, nanopore processing with different aspect ratios can be achieved, for example: nanopore processing with a aspect ratio of up to 4000:1 can be achieved.

[0029] The wet etching using an acidic solution is specifically as follows:

[0030] First, before the target object is placed in a container of an acidic aqueous solution, one surface of the target object is polished until a nanowire drawing induction region is exposed on the surface;

[0031] Secondly, the target workpiece was ultrasonically cleaned in deionized water, acetone, and alcohol for 5 min respectively;

[0032] Then, the target object is placed in a container of acidic solution, and the container is etched under ultrasonic oscillation disturbance; after the etching is completed, the target object is taken out and ultrasonically cleaned with deionized water, acetone, and alcohol for 5 minutes respectively to obtain a nanopore structure.

[0033] In wet etching with an acidic solution, the choice and concentration of the acidic solution, the presence or absence of heating, the presence and selection of oscillation conditions (magnetic stirring, ultrasound), and the etching time are all crucial factors in the successful formation of uniform, diameter-controlled nanopores with a high aspect ratio. By adjusting the optically isotropic crystal, such as the acidic solution concentration, heating temperature, the magnetic speed that accelerates the solution perturbation, and etching time, the femtosecond laser-induced nanofilamentous regions can be selectively controlled to form "nanopores with controllable pore size and a high aspect ratio."

[0034] The principle of this invention is that the crystal axes of an optically isotropic crystal are optically isotropic. When a femtosecond laser beam propagates through an optically isotropic crystal, it does not deflect or bifurcate. In contrast, the crystal axes of an optically anisotropic crystal are optically anisotropic. When a laser beam propagates through an optically anisotropic crystal, it is very likely to deflect and bifurcate, resulting in an uneven light field distribution.

[0035] In the present invention, an optically isotropic crystal is used to propagate a nanofilament-like localized uniform light field with enhanced spherical aberration into the interior of an optically anisotropic crystal, thereby inducing a uniform nanofilament modified region in the optically anisotropic crystal, which facilitates wet etching of a uniform nanopore structure by an acidic solution. Specifically, when a femtosecond laser passes through a thick optically isotropic crystal as an auxiliary material, the spherical aberration is significantly enhanced, thereby generating a plasma self-focusing effect to form a wiredrawing effect. The formed femtosecond laser nanofilaments are then focused into the interior of the optically anisotropic crystal of the target workpiece to form a localized nanofilament region, i.e., an induced region. By adjusting the focus depth of the femtosecond laser, the nanofilaments brought by the heat effect of the localized nanofilament region are ensured to act within the optically anisotropic crystal of the target workpiece. The femtosecond laser parameters are further adjusted to induce localized wiredrawing of the optically anisotropic crystal of the target workpiece. After the femtosecond laser induced wiredrawing, the atomic arrangement, chemical bond structure, and atomic looseness of the localized spatial material have changed, making the crystal material of the induced region completely different from that of the non-induced region.

[0036] The method further requires the use of acidic solution wet etching to quickly and selectively etch the femtosecond laser-induced nanofilamentous modified area without etching the crystalline material in the non-induced area, thereby forming a uniform nanopore structure with controllable pore size (30-300nm) and high aspect ratio (>4000:1) in the optically anisotropic crystal.

[0037] After the nanopores with controllable aperture and high aspect ratio are prepared by the present invention, they can be further used in various new nanophotonic devices, including: photonic crystal microcavity lasers, topological nanophotonic devices, continuous bound state nanophotonic devices, supersurface nanophotonic devices, etc. The present invention not only has high processing efficiency, good stability, relatively low cost, and can easily achieve the preparation of uniform 30nm deep holes, but also overcomes the shortcomings of traditional technology that can only process nanostructures on the surface of the material and the depth-to-diameter ratio of the processed nanostructures is very low. In addition, the nanopores with controllable aperture and high aspect ratio prepared by the present invention play a more unique and superior function in some new nanophotonic devices. For example: in the field of supersurface nanophotonic devices, traditional methods can only process low-depth-to-diameter-ratio convex supersurface nanophotonic structures, which hinders the development of large-scale, achromatic superlenses, broadband adjustable, and high laser damage threshold supersurface nanophotonic devices. However, the nanopores with controllable aperture and high aspect ratio prepared by the present invention not only provide a new solution for the design and preparation of hole-based metasurface nanophotonic devices, but also solve many problems faced by traditional methods in processing metasurface nanophotonic devices.

[0038] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0039] (1) Compared with traditional processing methods such as UV lithography, EBL, FIB, and RIE, the present invention is based on wet-assisted femtosecond laser processing of nanopore structures. The processing technology is simple, efficient, and low-cost. It can also induce processing of the three-dimensional space inside any optically anisotropic crystal and can adjust the preparation of nanopore structures with high aspect ratio.

[0040] (2) Compared with the general femtosecond laser direct writing technology, the present invention can process a "nanopore structure with controllable aperture and high aspect ratio" inside an optically anisotropic crystal, overcoming the disadvantage that the traditional technology can only process nanopore structures with low aspect ratio on the surface of the material. In addition, the mild method of wet etching can be fully utilized to not only prepare a smaller size (~λ / 35), uniform, and controllable nanopore structure, but also effectively avoid the longitudinal elongation effect brought about by the traditional femtosecond laser direct writing technology. In addition, there is a very large refractive index contrast (>0.7) between the formed nanopore and the non-induced crystal, which facilitates the design and preparation of high-performance nanophotonic devices.

[0041] (3) Compared with the femtosecond laser direct writing technology after beam shaping (such as Bessel beam), the shaped femtosecond laser beam is usually accompanied by severe sidelobe effects, resulting in uneven edges around the nanopore structure and even serious defects such as microcracks, which is not conducive to the design, preparation and performance improvement of nanophotonic devices. The present invention is simple to operate and can effectively overcome this shortcoming.

[0042] (4) The present invention overcomes the difficulty of directly processing uniform nanostructures in optically anisotropic crystals by femtosecond lasers. It cleverly uses optically isotropic crystals to enhance spherical aberration, forming a uniform nanofilament light field, and then propagating into the interior of the optically anisotropic crystal, prompting the femtosecond laser to form uniform localized nanofilaments in the self-focusing process inside the optically anisotropic crystal. The nanofilaments are confined to the nano-local space and can always remain uniform over a longer propagation path. They are also less likely to deflect or bifurcate, thereby inducing the microscopic atomic arrangement, chemical bond structure, and porosity of the modified material in the optically anisotropic crystal, making it easier to wet-etch "nanopores with controllable aperture and high aspect ratio" with an acidic solution. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 Schematic diagram of the wet-assisted femtosecond laser nano-machining method of the "nanopores with controllable aperture and high aspect ratio" in the optically anisotropic crystal of the present invention.

[0044] Figure 2 This is a scanning electron microscope (SEM) photo of the approximately 30 nm nanopores manipulated in optically anisotropic sapphire crystals using wet-assisted femtosecond laser nanomachining.

[0045] Figure 3 This is a scanning electron microscope (SEM) image of the approximately 300 nm nanopores manipulated in optically anisotropic sapphire crystals using wet-assisted femtosecond laser nanomachining.

[0046] Figure 4 Optical microscope photos of cross-sections at different stages of processing nanoholes in optically anisotropic sapphire crystals using wet-assisted femtosecond laser nanomachining method. DETAILED DESCRIPTION

[0047] The present invention will be further described in detail below with reference to the examples, but the embodiments of the present invention are not limited thereto.

[0048] The embodiments of the present invention are as follows:

[0049] Example 1

[0050] like Figure 1 Figure 2 shows a schematic diagram of wet-assisted femtosecond laser processing of a "nanopore with controllable aperture and high aspect ratio" in an optically anisotropic crystal. In this embodiment, a relatively thick, optically isotropic YAG crystal is used for spherical aberration enhancement, and a c-cut, optically anisotropic sapphire crystal is selected as the target material for wet-assisted femtosecond laser processing of the "nanopore with controllable aperture and high aspect ratio."

[0051] The method of wet-assisted femtosecond laser processing of a "nanopore with controllable aperture and high aspect ratio" in an optically anisotropic sapphire crystal in this embodiment mainly includes the following two steps:

[0052] 1) Based on the principle that thicker optically isotropic YAG crystals can effectively enhance the spherical aberration effect and significantly enhance the self-focusing effect of femtosecond lasers, wire drawing is performed inside an optically anisotropic sapphire crystal to induce nano-local spatial modification of the material;

[0053] Step 1) The parameters of the femtosecond laser used are: output laser wavelength 1030nm, pulse width 226fs, repetition rate 10kHz, laser power 60mW, linear polarization, and laser exposure pulse number 3pulse. The focusing objective parameters are: magnification 50x, numerical aperture NA=0.55, working distance WD=8.9mm. The thickness of the optically isotropic YAG crystal used for spherical aberration enhancement is about 3mm, and the thickness of the optically anisotropic sapphire Sapphire crystal of the target processing object is about 200μm. The two are optically contacted and stacked in sequence from top to bottom. The femtosecond laser is focused on a distance of about 60μm from the bottom surface of the optically anisotropic sapphire Sapphire crystal through the focusing objective lens, and local exposure drawing is performed to obtain a nanowire induction area with a length of about 120μm, such as Figure 4 As shown in a.

[0054] 2) Wet etching the wire drawing induction area using a hydrofluoric acid solution to form a nanopore structure.

[0055] First, the single side of the optically anisotropic sapphire crystal is polished until the end face of the material modification area induced by femtosecond laser self-focusing drawing is exposed ( Figure 4 b).

[0056] Secondly, the samples were ultrasonically cleaned with deionized water, acetone, and alcohol for 5 min each.

[0057] Then, a 30% hydrofluoric acid aqueous solution was used, the solution temperature was controlled at 37°C, the ultrasonic oscillation frequency was adjusted to the normal working frequency, and the etching time was 4 hours. After the etching was completed, the nanopore structure with a pore size of about 30nm was obtained by ultrasonic cleaning with deionized water, acetone, and alcohol for 5 minutes respectively. Figure 2 As shown in the SEM photos.

[0058] In this embodiment, a nanopore structure with a depth-to-diameter ratio of up to 4000:1 is obtained by simply extending the wet etching time to ensure that the 120 μm optically anisotropic sapphire crystal material modified area induced by femtosecond laser drawing is completely etched through. Figure 4 As shown in c.

[0059] Example 2

[0060] like Figure 1 Figure 2 shows a schematic diagram of wet-assisted femtosecond laser processing of a "nanopore with controllable aperture and high aspect ratio" in an optically anisotropic crystal. In this embodiment, a relatively thick, optically isotropic YAG crystal is used for spherical aberration enhancement, and a c-cut, optically anisotropic sapphire crystal is selected as the target material for wet-assisted femtosecond laser processing of the "nanopore with controllable aperture and high aspect ratio."

[0061] The method of wet-assisted femtosecond laser processing of a "nanopore with controllable aperture and high aspect ratio" in an optically anisotropic sapphire crystal in this embodiment mainly includes the following two steps:

[0062] 1) Based on the principle that thicker optically isotropic YAG crystals can effectively enhance the spherical aberration effect and significantly enhance the self-focusing effect of femtosecond lasers, wire drawing is performed inside an optically anisotropic sapphire crystal to induce nano-local spatial modification of the material;

[0063] Step 1) The parameters of the femtosecond laser used are: output laser wavelength 1030nm, pulse width 226fs, repetition rate 10kHz, laser power 220mW, linear polarization, and laser exposure pulse number 1pulse. The focusing objective parameters are: magnification 50x, numerical aperture NA=0.55, working distance WD=8.9mm. The thickness of the optically isotropic YAG crystal used for spherical aberration enhancement is about 3mm, and the thickness of the optically anisotropic sapphire Sapphire crystal of the target processing object is about 200μm. The two are optically contacted and stacked in sequence from top to bottom. The femtosecond laser is focused on a distance of about 60μm from the bottom surface of the optically anisotropic sapphire Sapphire crystal through the focusing objective lens, and local exposure drawing is performed to obtain a nanowire induction area with a length of about 120μm, such as Figure 4 As shown in a.

[0064] 2) Wet etching the wire drawing induction area using a hydrofluoric acid solution to form a nanopore structure.

[0065] First, the single side of the optically anisotropic sapphire crystal is polished until the end face of the material modification area induced by femtosecond laser self-focusing drawing is exposed ( Figure 4 b).

[0066] Secondly, the samples were ultrasonically cleaned with deionized water, acetone, and alcohol for 5 min each.

[0067] Then, a 30% hydrofluoric acid aqueous solution was used, the solution temperature was controlled at 37°C, the ultrasonic oscillation frequency was adjusted to the normal working frequency, and the etching time was 4 hours. After the etching was completed, the nanoporous structure with a pore size of about 300nm was obtained by ultrasonic cleaning with deionized water, acetone, and alcohol for 5 minutes respectively. Figure 2 As shown in the SEM photos.

[0068] In this embodiment, a nanopore structure with a depth-to-diameter ratio of up to 4000:1 is obtained by simply extending the wet etching time to ensure that the 120 μm optically anisotropic sapphire crystal material modified area induced by femtosecond laser drawing is completely etched through. Figure 4 As shown in c.

[0069] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A wet-assisted femtosecond laser processing method for optically anisotropic crystal nanopores, characterized in that: The method takes an optically anisotropic crystal to be processed as the target object, and specifically The following processes are included: First, another optically isotropic crystal thicker than the target workpiece is placed in optical contact on one side of the target workpiece as a spherical aberration enhancement auxiliary. A femtosecond laser is applied from the spherical aberration enhancement auxiliary to the target workpiece, transmitted through the spherical aberration enhancement auxiliary, and then incident and focused into the target workpiece. Then, the self-focusing wire-drawing inducing material inside the optically anisotropic crystal of the target workpiece is locally modified to form a nanowire-drawing inducing region. Different numbers of exposure pulses of the femtosecond laser are used. The target object is then wet-etched with an acidic solution, so that the nanowire drawing induction area is etched to form nanopores with controllable pore size and high aspect ratio.

2. The wet-assisted femtosecond laser processing method for optically anisotropic crystal nanopores according to claim 1, characterized in that: The material of the optically anisotropic crystal of the target workpiece is sapphire or lithium niobate crystal.

3. The wet-assisted femtosecond laser processing method for optically anisotropic crystal nanopores according to claim 1, characterized in that: The optically isotropic crystal material of the spherical aberration enhancement auxiliary is YAG, LuAG or diamond crystal.

4. The wet-assisted femtosecond laser processing method for optically anisotropic crystal nanopores according to claim 1, characterized in that: The femtosecond laser is focused on any relative position inside the optically anisotropic crystal as the target object through the focusing objective of the aspheric mirror for exposure, so that the microscopic atomic arrangement and looseness of the local space material of the crystal after exposure are changed, thereby forming a nano-wire drawing induction area.

5. The wet-assisted femtosecond laser processing method for optically anisotropic crystal nanopores according to claim 1, characterized in that: The aperture of the nanopore is regulated by the output wavelength, pulse width, repetition rate, power and number of exposure pulses of the femtosecond laser.

6. The wet-assisted femtosecond laser processing method for optically anisotropic crystal nanopores according to claim 4, characterized in that: The depth-to-diameter ratio of the nanopore is regulated by the refractive index of the optically anisotropic crystal as the target object, the thickness of the optically isotropic crystal as the auxiliary object, the working distance of the focusing objective lens, and the power of the femtosecond laser.

7. The wet-assisted femtosecond laser processing method for optically anisotropic crystal nanopores according to claim 1, characterized in that: The wet etching using an acidic solution is specifically as follows: First, before the target object is placed in a container of an acidic aqueous solution, one surface of the target object is polished until a nanowire drawing induction region is exposed on the surface; Secondly, the target workpiece was ultrasonically cleaned in deionized water, acetone, and alcohol respectively; Then, the target object is placed in a container of acidic solution, and the container is etched under ultrasonic oscillation disturbance; after the etching is completed, the target object is taken out and ultrasonically cleaned with deionized water, acetone, and alcohol respectively to obtain a nanopore structure.

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