A preparation method of a liquid-free zoom terahertz lens based on a superoleophobic and oleophilic surface

Abstract

A preparation method of a liquid-free zoom terahertz lens based on a superoleophobic-lipophilic surface, comprising the following steps: First step, select a solid substrate with a high terahertz transmittance, and etch induced microstructures on the substrate surface; Second step, after the etched substrate is cleaned with alcohol, it is immersed in a fluorosilane solution and then taken out and dried to carry out chemical modification to reduce the surface free energy of the solid substrate and construct the chemical components required for a superoleophobic surface; Third step, set a region where the liquid lens is to be formed, and perform a laser scan again on this set region with low power parameters to form a "lipophilic-superoleophobic" patterned hybrid surface; Fourth step, inject oil droplets into the lipophilic region of the "lipophilic-superoleophobic" surface, and under the action of surface tension, form a liquid terahertz lens with a uniform surface curvature. In the present invention, by slowly increasing or decreasing the liquid, the spherical curvature of the lens can be continuously changed, and stepless adjustment of the focal length can be achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of terahertz lenses, and particularly relates to a preparation method of a continuous zoom terahertz liquid lens based on a superoleophobic-lipophilic surface. Background Art

[0002] Terahertz (THz) waves occupy a very special position in the electromagnetic spectrum. It refers to electromagnetic waves with a frequency range of 0.1 - 10 THz (1 THz = 10 12 Hz). Its long wavelength band is adjacent to microwaves, and its short wavelength band is adjacent to infrared rays. Due to its special position in the electromagnetic spectrum, terahertz waves have some unique properties that infrared and microwaves do not have simultaneously. Such as low energy: referring to low single photon energy and no light damage to biological tissues; transient nature: the typical pulse width is in the picosecond range, with high time resolution and signal-to-noise ratio; broadband nature: most terahertz sources can emit wide-spectrum signals ranging from GHz to dozens of THz, which can be used for spectral detection. High penetrability: terahertz waves have strong penetration ability for organic substances and non-polar substances. Due to the above characteristics, terahertz waves have broad application prospects in the fields of imaging, medical diagnosis, communication, biochemistry, security detection, etc. In practical applications, it is first necessary to manipulate terahertz waves such as focusing, diverging, reflecting, and refracting. Lenses are essential basic devices for manipulating terahertz waves.

[0003] Common terahertz lenses are mostly prepared from solid materials, such as crystal materials like high-resistance silicon, quartz, sapphire, and polymer materials like PE, PP, PTEF, and TPX. However, compared with liquid lenses, once a solid lens is formed, optical parameters such as focal length cannot be changed, and changing the focal length can only be achieved by replacing the lens. In addition, the production cycle and cost of solid lenses are relatively high. Oil-based materials such as white oil and insulating oil have high transmittance in the terahertz band, are not easily volatile, have a certain surface tension, and are in a stable state when static, making them suitable terahertz lens materials. However, since it is not easy to manipulate liquids to form lenses, there is still little research on the development of liquid terahertz lenses. There is only one example of a liquid terahertz lens that can be found, and its manufacturing method refers to the manufacturing method of liquid lenses in the visible light band, with a similar basic idea, but it is not very suitable in the terahertz band. This method requires a container to hold the liquid and inject ions into the liquid, and relies on an external electric field to control the surface curvature of the liquid, which has many drawbacks.

[0004] As described above, first, compared with liquid lenses, solid lenses are costly to fabricate and cannot be focused during use, making them less flexible than liquid lenses. Second, existing liquid lenses are costly to fabricate and not very convenient to use, as they require a lens body combined with an external electric field for operation. Additionally, existing lenses are fabricated by injecting ions into an oily liquid. However, terahertz waves are strongly absorbed by polar substances, and injecting ions will significantly reduce the transmittance of terahertz waves. Without injecting ions, the lens cannot achieve focusing. Therefore, the practical application effect of this method is poor, and this fabrication method directly referencing the visible light band is not very suitable for the terahertz band. Moreover, the focusing ability of this method is limited. This method relies on an external electric field to change the curvature of the lens surface. After applying the electric field, the ions injected into the liquid lens move directionally under the action of the electric field force, driving the liquid surface to stretch from a plane to a curved surface. However, the stretching ability is limited and cannot form a curved surface with a small curvature. Summary of the Invention

[0005] To overcome the problems existing in the above prior art, the object of the present invention is to provide a method for preparing a terahertz liquid lens with infinite zoom based on a superoleophobic-lipophilic surface. This method first selects a non-polar liquid with a very high terahertz transmittance and not easily volatile at room temperature, such as white oil, as the lens material. Then, a superoleophobic-lipophilic patterned hybrid surface is prepared on a solid substrate such as silicon using a superoleophobic surface preparation method such as laser micro-nano processing. Finally, the liquid is injected into the lipophilic region, and under the action of gravity and surface tension, the oil droplet naturally forms a plano-convex liquid lens with a flat bottom surface and a spherical top surface. By slowly increasing or decreasing the liquid, the spherical curvature of the lens can be continuously changed to achieve infinite adjustment of the focal length.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] A method for preparing a terahertz liquid lens with infinite zoom based on a superoleophobic-lipophilic surface, comprising the following steps;

[0008] In the first step, a solid substrate with high terahertz transmittance is selected, and induced microstructures are etched on the substrate surface to construct the surface micro-nano morphology required for a superoleophobic surface;

[0009] In the second step, the etched substrate is cleaned with alcohol and then immersed in a fluorosilane solution and taken out to dry, so as to carry out chemical modification to reduce the surface free energy of the solid substrate and construct the chemical composition required for a superoleophobic surface; after these two steps, this surface becomes a superoleophobic surface;

[0010] In the third step, set a region where the liquid lens is formed. On this set region, perform a laser scan again with low-power parameters to remove the chemical modification layer in this region, thereby turning this region into an oleophilic region, while the region outside remains a superoleophobic region. The region where the chemical modification layer is removed by this scan shows an oleophilic region because the surface energy becomes the intrinsic surface free energy of silicon. Thus, a "oleophilic-superoleophobic" patterned hybrid surface is formed, with the second scan region as the oleophilic region and all regions outside the oleophilic region as the superoleophobic region.

[0011] In the fourth step, inject oil droplets into the oleophilic region of the "oleophilic-superoleophobic" patterned hybrid surface. The injected oil droplets are automatically adhered under the oleophilic action and spread and halo in this region. After the boundary of the oil droplet expands to the junction of the oleophilic and superoleophobic regions, the expansion stops due to the oleophobic action of the superoleophobic surface, and the oil droplet boundary stops at the "oleophilic-superoleophobic" junction. After continuously injecting oil droplets, the upper surface of the oil droplet bulges naturally, and under the action of surface tension, a liquid terahertz lens with a uniform surface curvature is formed.

[0012] The specific content of the first step is as follows: The solid substrate material with high transmittance is silicon; induce microstructures on the substrate surface by laser etching.

[0013] The specific method and conditions of the laser etching are as follows: Use a scanning galvanometer to control the laser focused spot to etch along a cross pattern with a spacing of 20 - 60 μm as the scanning path. The average power of the laser is generally 5 - 30 W, the pulse repetition frequency is 10 - 30 KHz, and the diameter of the focused spot is 10 - 50 μm.

[0014] The structural characteristics of the microstructures are as follows: After laser etching, the area scanned by the spot is ablated and removed, forming a micron-scale cross-groove structure; at the same time, a rich layer of nanoparticles is deposited on the surface by the "melting - ejection - deposition" action during the laser ablation process, thus constituting a micro-nano composite structure in the shape of cross grooves.

[0015] The parameter limiting conditions of the laser scan are as follows: The scanning spacing of the cross grooves should generally be between 40 μm and 100 μm, and the groove depth is between 10 μm and 50 μm; the average power of the laser is generally 5 - 30 W, the pulse repetition frequency is not greater than 30 KHz, the pulse width is not greater than 20 ns, and the diameter of the focused spot is not greater than 50 μm.

[0016] In the second step, soak in the fluorosilane solution for generally about 30 - 60 min;

[0017] The solution concentration of the fluorosilane solution is a 2% - 8% mass concentration of fluorosilane isopropanol solution. After the soaking ends, stand it up to dry and heat it on a heating platform at 100 - 120 °C for 30 - 60 min.

[0018] In the third step: The set area is selected according to the aperture of the liquid lens to be formed, generally a circular area with a diameter of 2 - 10 mm.

[0019] The limiting conditions for the low-power parameter laser scanning are: Scanning is performed along the cross-groove path, the scanning pitch should be between 3 μm and 10 μm, and the average laser power should not be greater than 3 W; other laser parameters remain unchanged, that is, the pulse repetition frequency is not greater than 30 KHz, the pulse width is not greater than 20 ns, and the focused spot diameter is not greater than 50 μm. The purpose of this step is to just remove the modification layer in the way of low-power dense light scanning, and should not significantly change the micron-scale morphology.

[0020] In the fourth step, since the oil-wetting area and the super-oil-repellent area have completely different wetting properties for oil, when white oil is injected into the oil-wetting area, the white oil will immediately wet the entire oil-wetting area and will not wet beyond the boundary of the oil-wetting - super-oil-repellent area and enter the super-oil-repellent area; therefore, when increasing or decreasing the liquid, the contact area between the white oil and the solid substrate is always only in the oil-wetting area of the substrate; furthermore, since the area size of the bottom surface no longer changes, the upper surface of the liquid will bulge naturally when increasing the liquid, the curvature becomes smaller, and will fall flat naturally when decreasing the liquid, the curvature increases. Thus, the curvature of the lens is adjusted by increasing and decreasing the liquid.

[0021] The oil droplet is white oil.

[0022] The liquid terahertz lens is composed of a high-resistance silicon solid substrate with a thickness of about 0.5 mm and about 0.1 - 2 mL of white oil; among them, the solid substrate serves as the carrier of the lens, and the white oil serves as the lens body;

[0023] During operation, white oil is injected onto the oil-wetting area of the solid substrate. Due to the special wettability, the white oil will only wet the oil-wetting area, and then the edge where the white oil contacts the substrate can remain fixed; when adding a little more white oil, its upper surface will bulge slightly, forming a convex surface, forming a spherical-crowned plano-convex shape, and thus can be used as a lens.

[0024] When adjusting the focal length, only by increasing or decreasing the white oil in the oil-wetting area can the shape curvature of the upper surface of the liquid be changed, and thus the focal length be changed;

[0025] Its characteristic is that the lens body is liquid, and the lens shape can be freely changed, and the focusing is flexible.

[0026] In the liquid terahertz lens, when the diameter D of the circular oil-wetting region is set to D = 2 mm, a zoom range from approximately zero to infinity can be achieved; when less than 0.5 μL of liquid is added, the surface is approximately flat and the focal length is approximately infinity; when the liquid increases to 10 μL, the liquid terahertz lens body is an approximately spherical shape with a diameter of 3 mm. At this time, the focus is very close to the lower surface of the lens, approximately f≈0;

[0027] When the diameter of the circular oil-wetting region is set in the range of 4 mm < D < 10 mm, the maximum value of the zoom range is f≈infinity, and the minimum value is determined by D, approximately f≈D / 2;

[0028] When the diameter of the circular oil-wetting region is set in the range of 2 mm < D < 4 mm, the maximum value of the zoom range is f = infinity, and the minimum value is between 0 and 2 mm; when D = 2 mm, f≈0, and when D = 4 mm, f≈2 mm; among them, when D = 2 mm, the liquid lens volume can form an approximately spherical shape at its maximum, and at this time f≈0; when D = 4 mm, the liquid lens volume can only form a hemisphere at its maximum, and at this time f≈D / 2.

[0029] Advantages of the present invention:

[0030] 1. First, this liquid lens is different from solid lenses. It has an unfixed shape at room temperature, so the lens curvature can be flexibly adjusted to change the focal length.

[0031] 2. Second, the manufacturing principle of this lens is different from the previously proposed method of applying an electric field to form a convex surface. Its basic principle is based on the different interfacial behaviors of oil-wetting surfaces and super-oleophobic surfaces towards oil-based liquids. This method is simple to manufacture and easy to control the quality.

[0032] 3. In addition, due to its different manufacturing principle, this lens does not need to be doped with cations and anions. The lens material composition is a single pure oil-based liquid white oil, so it has a stable refractive index and high transmittance.

[0033] 4. Moreover, the method of adjusting the focal length of this lens is to increase or decrease the liquid. Continuous and slow adjustment can achieve stepless zooming. The operation is simple and flexible, and the practicability is relatively strong. There is no need to use an external electric field to control the focusing.

[0034] 5. Finally, this lens has a very large zoom range. When the diameter D of the circular oil-wetting region is set to D = 2 mm, a zoom range from approximately zero to infinity can be achieved. When very little liquid is added (less than 0.5 μL), the surface is approximately flat and the focal length is approximately infinity; when the liquid increases to the maximum (about 10 μL), the lens body is an approximately spherical shape with a diameter of about 3 mm. At this time, the focus is very close to the lower surface of the lens, approximately f≈0.

[0035] When the diameter of the circular oil-wetting area is set in the range of 4 mm < D < 10 mm, the maximum value of the zoom range is f ≈ infinity, and the minimum value is determined by D, approximately f ≈ D / 2. This is because when D is in this size range, the upper surface of the liquid lens bulges to a semi-circle at most, corresponding to a minimum curvature of D / 2, and at this time the focal length is approximately f ≈ D / 2.

[0036] When the diameter of the circular oil-wetting area is set in the range of 2 mm < D < 4 mm, the maximum value of the zoom range is f = infinity, and the minimum value is between 0 and 2 mm. When D = 2 mm, f ≈ 0; when D = 4 mm, f ≈ 2 mm. This is because when D is in this size range, the liquid lens is in a state between a sphere and a hemisphere. Among them, when D = 2 mm, the liquid lens can form an approximate sphere with the largest volume, and at this time f ≈ 0; when D = 4 mm, the liquid lens can only form a hemisphere with the largest volume, and at this time f ≈ D / 2. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a schematic diagram of the process of the present invention.

[0038] Figure 2 It is a schematic diagram of the continuous focusing process of the terahertz liquid lens based on the superoleophobic-oleophilic surface of the present invention.

[0039] Reference numerals:

[0040] In the figure: 1 - Laser microfabrication system; 2 - Solid substrate; 3 - Solid substrate with surface microstructure; 4 - Fluorosilane solution; 5 - Solid substrate with superoleophobic surface; 6 - Superoleophobic region; 7 - Oleophilic region; 8 - Solid substrate with "oleophilic-superoleophobic" patterned hybrid surface; 9 - Liquid material; 10 - Liquid terahertz lens. DETAILED DESCRIPTION OF THE INVENTION

[0041] The present invention will be further described in detail below with reference to the accompanying drawings.

[0042] Example 1:

[0043] As Figure 1 shown: A preparation method of an infinitely variable zoom terahertz liquid lens based on a superoleophobic-oleophilic surface, comprising the following steps;

[0044] First step, select a solid substrate with high terahertz transmittance, induce microstructures on the substrate surface, and construct the surface micro-nano morphology required for the superoleophobic surface;

[0045] Second step, after etching the substrate, clean it with alcohol, soak it in the fluorosilane solution and then take it out to dry, so as to carry out chemical modification to reduce the surface free energy of the solid substrate and construct the chemical components required for the superoleophobic surface; after these two steps, this surface becomes a superoleophobic surface;

[0046] In the third step, set a region where the liquid lens is to be formed. On this set region, perform a laser scan again with low-power parameters to remove the chemical modification layer in this region, thereby turning this region into an oil-wetting region, while the region outside remains a super-oil-repellent region, thus forming an "oil-wetting - super-oil-repellent" patterned hybrid surface;

[0047] In the fourth step, inject oil droplets into the oil-wetting region of this "oil-wetting - super-oil-repellent" surface. The injected oil droplets are automatically adhered under the action of oil-wetting and spread and halo in this region. After the boundary of the oil droplet expands to the junction of the oil-wetting and super-oil-repellent regions, the expansion stops due to the oil-repellent action of the super-oil-repellent surface, and the oil droplet boundary stops at the "oil-wetting - super-oil-repellent" junction. After continuously injecting oil droplets, the upper surface of the oil droplet bulges naturally, and under the action of surface tension, a liquid terahertz lens with a uniform surface curvature is formed.

[0048] The specific content of the first step is as follows: The solid substrate with high transmittance is made of silicon; induce microstructures on the substrate surface by laser etching.

[0049] The specific method and conditions of the laser etching are: Use a scanning galvanometer to control the laser focused spot to etch along a cross pattern with a 50-μm pitch as the scanning path. The average power of the laser is 20 W, the pulse repetition frequency is 20 KHz, and the diameter of the focused spot is 25 μm.

[0050] The structural characteristics of the microstructures are: After laser etching, the area scanned by the light spot is ablated and removed, forming a micron-scale cross-groove structure; at the same time, a layer of rich nanoparticles is deposited on the surface by the "melting - ejection - deposition" action during the laser ablation process, thus constituting a micro-nano composite structure in the shape of a cross groove.

[0051] The parameter limiting conditions of the laser scan are: The scanning pitch of the cross groove is 50 μm, and the groove depth is 20 μm; the average power of the laser is 20 W, the pulse repetition frequency is 20 KHz, the pulse width is 15 ns, and the diameter of the focused spot is 30 μm.

[0052] In the second step, soak in the fluorosilane solution for about 40 min;

[0053] The solution concentration of the fluorosilane solution is a 3% mass concentration of fluorosilane isopropanol solution. After soaking, dry it by heating on a heating platform at 120° for 30 min.

[0054] In the third step: The set region is a circular region with a diameter of 5 mm according to the aperture of the liquid lens to be formed.

[0055] The defined conditions for the low-power parameter laser scanning are as follows: the scanning pitch of the cross grooves is 5 μm, and the average laser power is 2 W; other laser parameters remain unchanged, namely the pulse repetition frequency is 20 KHz, the pulse width is 15 ns, and the focused spot diameter is 30 μm.

[0056] The oil droplet is white oil.

[0057] The liquid terahertz lens is composed of a high-resistance silicon solid substrate with a thickness of about 0.5 mm and about 1 mL of white oil; among them, the solid substrate serves as the carrier of the lens, and the white oil serves as the lens body;

[0058] 1. As a further improvement of the technical solution of the present invention, the liquid material can also be other non-polar liquids other than white oil, including: vegetable oil, mineral oil, lubricating oil, electrical insulating oil, etc.

[0059] 2. As a further improvement of the technical solution of the present invention, for the preparation technology of the oil-loving and super-oil-repellent patterned hybrid surface, the preparation of the super-oil-repellent surface by laser micro-nano processing is the preferred solution, and it can also be: the preparation of super-oil-repellent by chemical vapor deposition, the preparation of super-oil-repellent by spin coating, the preparation of super-oil-repellent by magnetron sputtering and other methods.

[0060] 3. As a further improvement of the technical solution of the present invention, for the solid substrate for preparing the super-oil-repellent surface, silicon is only a preferred solution, including but not limited to other solid substrates that can transmit terahertz waves, such as PE, PP, PTFE, TPX, etc.

[0061] As Figure 2 shown: In the fourth step, due to the completely different wetting characteristics of the oil-loving area and the super-oil-repellent area for oil, when white oil is injected into the oil-loving area, the white oil will immediately wet the entire oil-loving area without wetting beyond the boundary of the oil-loving and super-oil-repellent areas and entering the super-oil-repellent area; therefore, when increasing or decreasing the liquid, the contact area between the white oil and the solid substrate is always only in the oil-loving area of the substrate; furthermore, since the area of the bottom surface no longer changes, the upper surface of the liquid will bulge naturally when increasing the liquid, with a smaller curvature, and will fall flat naturally when decreasing the liquid, with an increased curvature. Thus, the curvature of the lens is adjusted by increasing and decreasing the liquid.

[0062] The liquid terahertz lens is composed of a high-resistance silicon solid substrate with a thickness of about 0.5 mm and about 0.1 - 2 mL of white oil; among them, the solid substrate serves as the carrier of the lens, and the white oil serves as the lens body;

[0063] During operation, white oil is injected onto the oil-loving area of the solid substrate. Due to the special wettability, the white oil will only wet the oil-loving area, and then the edge where the white oil contacts the substrate can remain fixed; when adding a slightly larger amount of white oil, its upper surface will bulge slightly to form a convex surface, forming a spherical crown-shaped plano-convex shape, and thus can be used as a lens;

[0064] When adjusting the focal length, it is only necessary to increase or decrease the white oil in the lipophilic region, which can change the shape curvature of the upper surface of the liquid, and then change the focal length.

[0065] Its characteristic is that the lens body is a liquid, which can freely change the lens shape and has flexible focusing.

[0066] In the present invention, the basic principle realized by the liquid lens is based on the preparation of a patterned hybrid "lipophilic - super - oleophobic" surface substrate. In the lipophilic region of the silicon substrate, the solid surface free energy is higher than the surface energy of the oil, and this region shows lipophilicity, and the oil droplet completely wets the lipophilic region; in the super - oleophobic region, the solid surface free energy is lower than the surface energy of the oil, and the oil droplet is completely repelled by the super - oleophobic surface and cannot be wetted. Therefore, on both sides of the boundary between the lipophilic region and the super - oleophobic region, the oil droplet shows completely different wetting characteristics. The oil dropped into the lipophilic region will no longer spread when it reaches the super - oleophobic boundary, and the boundary of the oil droplet will be fixed at the junction of the lipophilic and super - oleophobic regions without spreading into the super - oleophobic region at all. An oil - based liquid lens with only the lipophilic region as the aperture is formed. As Figure 2 shown, when a small amount of liquid is injected into the lipophilic region, the liquid quickly wets the lipophilic region and forms a thin oil film layer with a circular aperture. When the liquid is continuously increased, the contact surface between the liquid and the solid will not continue to expand. Therefore, the upper surface of the oil film slowly bulges due to the increase in the liquid. Under the action of gravity and surface tension, the upper surface of the oil droplet naturally forms a spherical surface, and the bottom surface fits the substrate as a plane, and the whole lens is a plano - convex lens. When more liquid is added continuously, the "solid - liquid - gas" three - phase line composed of the oil droplet, the substrate and the air will not move, and the boundary of the oil droplet remains pinned at the lipophilic - super - oleophobic junction, forming an aperture with a fixed size. Thus, the upper surface of the oil film can be "more convex", so that the curvature of the lens is smaller and the focal length is smaller; on the contrary, when the liquid is slowly reduced, the boundary of the oil droplet still remains pinned at the lipophilic - super - oleophobic junction, and the aperture size remains fixed. Thus, the upper surface of the oil film becomes "flatter", so that the curvature of the lens is larger and the focal length is larger; therefore, the focal length of the liquid lens can be flexibly adjusted by simply adding or reducing the liquid.

[0067] Since the addition and reduction of the liquid can change continuously, the focal length of the lens can be adjusted steplessly and the adjustment range is very large.

[0068] The focusing process of the liquid lens is as shown in the appendix Figure 2As shown, when there is very little liquid, its upper surface is almost flat, and at this time it has the maximum focal length, approximately at infinity; when the liquid is gradually increased, the position of the liquid edge will not expand, maintaining a constant aperture, and its upper surface gradually bulges, the curvature gradually becomes smaller, and the focal length decreases; when the liquid volume increases to the maximum, the shape of the liquid lens is spherical (when D = 2 mm), at this time the focus is near the lower surface of the substrate, and the focal length is approximately f≈0; or a small part of the sphere is cut off (when 2 mm < D < 4 mm), the focus is near the lower surface of the substrate, and the minimum focal length is between f≈0 and f≈2 mm; or hemispherical (when 4 mm < D < 10 mm), at this time, the minimum focal length is related to D and is f≈D / 2.

[0069] The above content is only to illustrate the technical idea of the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution according to the technical idea proposed by the present invention fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing a stepless zoom terahertz liquid lens based on a super oleophobic-oleophilic surface, characterized in that: It includes the following steps; In the first step, select a solid substrate with high terahertz transmittance, etch induced microstructures on the substrate surface, and construct the surface micro-nano topography required for a superoleophobic surface; In the second step, chemically modify the etched substrate to reduce the surface free energy of the solid substrate and construct the chemical composition required for a superoleophobic surface; after these two steps, the surface becomes a superoleophobic surface; In the third step, set a region where the liquid lens is to be formed. On this set region, perform a laser scan again to remove the chemical modification layer in this region. The region where the chemical modification layer is removed by this scan shows an oleophilic region because the surface energy becomes the intrinsic surface free energy of silicon, thus forming an "oleophilic-superoleophobic" patterned hybrid surface with the second scan region as the oleophilic region and all regions outside the oleophilic region as the superoleophobic region; In the fourth step, inject an oil droplet into the oleophilic region of the "oleophilic-superoleophobic" patterned hybrid surface. The upper surface of the oil droplet bulges naturally, and under the action of surface tension, a liquid terahertz lens with a uniform surface curvature is formed; The specific content of the first step is as follows: the solid substrate with high transmittance is made of silicon; laser etching is used to induce microstructures on the substrate surface; The specific method and conditions of the laser etching are: the scanning pattern of the laser etching is a cross groove or a parallel line groove; The scanning pitch of the cross or parallel line grooves should be between 40μm and 100μm, and the depth of the etched grooves is between 10μm and 50μm; The structural characteristics of the microstructures are as follows: after laser etching, the area scanned by the light spot is ablated and removed, forming a micron-scale cross groove structure; at the same time, a rich layer of nanoparticles is deposited on the surface by the "melting-injection-deposition" during the laser ablation process, constituting a micro-nano composite structure in the shape of a cross groove.

2. A method for preparing a stepless zoom terahertz liquid lens based on a super oleophobic-oleophilic surface according to claim 1, characterized in that, The parameter limiting conditions of the laser scan are: the average laser power is 5 - 30W, the pulse repetition frequency is not greater than 30KHz, the pulse width is not greater than 20ns, and the focused light spot diameter is not greater than 50um; 3. The method for preparing a stepless zoom terahertz liquid lens based on a super oleophobic-oleophilic surface according to claim 1, wherein In the second step, after washing the etched substrate with alcohol, immerse it in a fluorosilane solution, take it out and dry it. The immersion in the fluorosilane solution is for 20 - 60min; The solution concentration of the fluorosilane solution is a 3% mass concentration of fluorosilane isopropanol solution. After the immersion, stand it up to dry and heat it on a heating platform at 100 - 120°C for 30 - 60min.

4. The preparation method of an achromatic zoom terahertz liquid lens based on a superoleophobic-lipophilic surface according to claim 1, characterized in that, In the third step: the set region is selected according to the aperture of the liquid lens to be formed, a circular region with a diameter of 2 - 10mm.

5. The preparation method of an achromatic zoom terahertz liquid lens based on a superoleophobic-lipophilic surface according to claim 1, wherein Perform a laser scan again with low power parameters. The limiting conditions of the laser scan with low power parameters are: the scanning pitch of the cross grooves should be between 3μm and 5μm, and the average laser power is not greater than 3W; other laser parameters remain unchanged, that is, the pulse repetition frequency is not greater than 30KHz, the pulse width is not greater than 20ns, and the focused light spot diameter is not greater than 50um; The oil droplet is white oil.

6. The liquid terahertz lens obtained by the method according to any one of claims 1 to 5, characterized in that: The liquid terahertz lens is composed of a high-resistance silicon solid substrate with a thickness of about 0.5mm and about 0.1 - 2mL of white oil; among them, the solid substrate serves as the carrier of the lens, and the white oil serves as the lens body; During operation, white oil is injected onto the lipophilic region of the solid substrate. Due to the special wettability, the white oil will only wet the lipophilic region, and thus the edge where the white oil contacts the substrate can remain fixed. When a slightly larger amount of white oil is added, its upper surface will bulge slightly, forming a convex surface and a spherical crown-shaped plano-convex shape, serving as a lens. When adjusting the focal length, it is only necessary to increase or decrease the white oil in the lipophilic region to change the shape curvature of the upper surface of the liquid, and thus change the focal length. Its characteristic is that the lens body is a liquid, and the lens shape can be freely changed, enabling flexible focusing.

7. The liquid terahertz lens according to claim 6, characterized in that ； In the described liquid terahertz lens, when the diameter D of the circular lipophilic region is set to D = 2 mm, a zoom range from approximately zero to infinity can be achieved; when less than 0.5 μL of liquid is added, the surface is approximately planar and the focal length is approximately infinity; when the liquid is increased to 10 μL, the liquid terahertz lens body is an approximately spherical shape with a diameter of 3 mm, and at this time the focus is very close to the lower surface of the lens, approximately f ≈ 0. When the diameter of the circular lipophilic region is set in the range of 4 mm < D < 10 mm, the maximum value of the zoom range is f ≈ infinity, and the minimum value is determined by D, approximately f ≈ D / 2. When the diameter of the circular lipophilic region is set in the range of 2 mm < D < 4 mm, the maximum value of the zoom range is f = infinity, and the minimum value is between 0 and 2 mm; when D = 2 mm, f ≈ 0, and when D = 4 mm, f ≈ 2 mm; among them, when D = 2 mm, the liquid lens can form an approximately spherical shape with the largest volume, and at this time f ≈ 0; when D = 4 mm, the liquid lens can only form a hemisphere with the largest volume, and at this time f ≈ D / 2.

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