High-threshold high-anti-reflection laser window and manufacturing method thereof

Abstract

The invention discloses a high-threshold high-anti-reflection laser window and a manufacturing method thereof, and belongs to the field of micro-nano optical processing. According to the method, traditional precious metal and high-temperature annealing processes are abandoned, and low-melting-point soft metal is adopted as an evaporation film material. The method comprises the following steps: heating an optical substrate to 80-200 DEG C in a vacuum environment, maintaining the temperature, and carrying out at least two times of cyclic deposition by utilizing an electron beam evaporation technology; in each deposition, metal is self-assembled on the surface of the heating substrate through a dehumidification effect to form spherical nano-particles, the particles continue to grow on an original array through subsequent deposition, and finally the spherical nano-metal mask with high uniformity and high filling degree is obtained. And etching by taking the mask as a protective layer, transferring the appearance of the mask to the surface of the substrate to form a micro-nano structure, and cleaning to obtain the laser window. The method is simple in process, low in cost and suitable for large-area manufacturing, and the obtained window has the high laser damage threshold value, the high transmittance and the self-cleaning surface characteristic.

Description

Technical Field

[0001] This invention belongs to the field of micro-nano optical processing, specifically relating to a high-threshold, high-transmittance laser window and its manufacturing method. Background Technology

[0002] With the development of high-power laser technology, the performance requirements for laser windows are becoming increasingly stringent. They not only need to possess a high laser damage threshold and excellent optical transmittance, but also require comprehensive functions such as self-cleaning, anti-fouling, and long lifespan. Traditional laser windows often rely on multilayer dielectric films for antireflection, but these films are prone to thermal damage and film delamination under high-energy laser irradiation, and their fabrication process is complex and costly.

[0003] In recent years, optical surfaces based on micro / nano structures (such as moth-eye structures and nanopillar arrays) have shown great potential in high-power laser windows due to their ability to precisely control the light field. These structures can achieve high transmission over a wide wavelength range and large angles, and due to their material integration, they possess higher laser damage thresholds and better environmental stability. Mask-induced etching is one of the mainstream techniques for fabricating these micro / nano structures, and its core lies in preparing high-quality nanomasks on the substrate surface.

[0004] Currently, nanoscale metal masks have attracted widespread attention due to their suitability for large-area, high-efficiency fabrication. Conventional methods often employ high-melting-point noble metals such as gold (Au), silver (Ag), and platinum (Pt), using physical vapor deposition combined with high-temperature annealing to cause the metal film to agglomerate and form nanoscale island-like masks. However, this method has significant drawbacks: First, noble metals are expensive, hindering large-scale applications; second, the agglomeration requires high strain energy, necessitating a high-temperature annealing process, which is energy-intensive and may cause thermal stress on the substrate material; third, the formed metal nanoparticles are often unevenly distributed, have low filling density, and poor shape and size consistency, resulting in poor uniformity of the micro / nanostructures obtained through subsequent etching, directly affecting the anti-reflection effect of the window and the laser damage threshold; furthermore, the stability (etch selectivity) of such masks during wet or dry etching processes is often unsatisfactory.

[0005] Therefore, there is an urgent need to develop a new method that is low-cost, simple to process, does not require high-temperature annealing, and can produce nano-metal masks with high uniformity and high filling degree. Based on this method, high-threshold, high-transmission laser windows with excellent performance can be manufactured to meet the increasingly higher reliability and functionality requirements of optical components in high-power laser systems. Summary of the Invention

[0006] To overcome the shortcomings of the prior art, this invention provides a high-threshold, high-reflection laser window and its manufacturing method. It utilizes a low-melting-point soft metal and directly prepares a nano-metal mask on the substrate surface via electron beam evaporation, eliminating the need for traditional precious metal annealing processes. The entire process requires only multiple cycles of electron beam evaporation, resulting in high efficiency and low cost.

[0007] The technical solution adopted in this invention is as follows: A method for manufacturing a high-threshold, high-reflection laser window, characterized by comprising the following steps: Step (1) Mask preparation: Use a low melting point soft metal with a melting point below 280℃ as the evaporation film material, and put the cleaned optical substrate into the vacuum chamber; Step (2) Cyclic deposition of self-assembled mask: In the vacuum chamber, the optical substrate is heated and maintained at a first specific temperature, which is in the range of 80°C to 200°C and is lower than the melting point of the selected low-melting-point soft metal; using electron beam evaporation technology, the low-melting-point soft metal is deposited on the heated substrate surface at a first deposition amount, and the deposited metal spontaneously agglomerates at the first specific temperature through a dehumidification effect to form an initial spherical nano-metal particle array; the electron beam evaporation deposition process is cyclically executed at least twice, and in at least one subsequent cycle, the substrate is reheated and maintained at a second specific temperature, which is in the range of 80°C to 200°C and is lower than the melting point of the selected low-melting-point soft metal, and then the low-melting-point soft metal is deposited again at a second deposition amount, so that the metal particles continue to grow on the basis of the original array, thereby obtaining a spherical nano-metal mask with high filling degree, wherein the first deposition amount and the second deposition amount are 10nm to 100nm respectively; Step (3) Window structure etching: Using the spherical nano metal mask obtained in step (2) above as a protective layer, the substrate is etched to transfer the morphology of the mask to the substrate surface and form the micro-nano structure of the laser window surface. Step (4) Post-processing cleaning: Remove the mask material and etching products remaining on the surface of the window after etching, clean and dry to obtain the high threshold and high transmittance laser window.

[0008] Furthermore, in step (1), the low-melting-point soft metal is a metal with a melting point below 280°C, ductility, and is non-toxic and harmless, and the metal is selected from any one of Sn, Bi, and ln.

[0009] Furthermore, in step (1), the optical substrate is selected from any one of BK7, fused silica, SF5, LAK14, and K9 glass.

[0010] Furthermore, in step (2), the first specific temperature is the same as or different from the second specific temperature, and / or the first deposition amount is the same as or different from the second deposition amount.

[0011] Furthermore, in step (2), the cycle is executed at least twice, including 2, 3, 4 or 5 times, and the total number of cycles is N, so that a spherical nano-metal mask is obtained after N deposition growths.

[0012] Furthermore, in step (3), the etching process is wet chemical etching or dry physical etching.

[0013] Furthermore, the wet chemical etching is hydrofluoric acid etching, and the dry physical etching is ion beam etching.

[0014] Furthermore, the cleaning step (4) is as follows: (1) Immerse the laser window in a mixed solution of oxalate and acid for 60 minutes, wherein the oxalate concentration is 5-30%. The acid solution concentration is 5-20 mol / L, and the volume mixing ratio is 1:1.

[0015] (2) Take out the sample, rinse it with deionized water for 10 minutes, and blow it dry with high-purity nitrogen. On the other hand, the present invention also provides a laser window, characterized in that it is manufactured by the above method.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: 1) Low-melting-point soft metals (Sn, Bi, ln, etc.) are used to replace traditional noble metals (Au, Ag, Pt, etc.) as nanomask materials. The heating temperature of the substrate during electron beam evaporation (80-200℃) triggers the "dehumidification" self-assembly behavior of the metal film, realizing "deposition and forming". This eliminates the high-temperature annealing step required in traditional processes, which not only significantly reduces material and energy costs, but also avoids potential damage to heat-sensitive substrates.

[0017] 2) By controlling the number of cycles (1-5 times) and the temperature and deposition parameters in each cycle, the size, distribution density and filling degree of nano-metal particles can be precisely controlled, effectively overcoming the shortcomings of small particle size, sparse distribution and low filling degree in single deposition. High uniformity and high filling degree of spherical nano-metal masks can be directly prepared, laying a solid foundation for etching high-performance micro and nano structures.

[0018] 3) Combining vacuum baking technology with the physical properties of low-melting-point metals has resulted in a novel, integrated mask fabrication solution. This solution features a simple process, with the entire process primarily completed in a vacuum coating machine. It is easy to control, has good repeatability, and is highly suitable for the mass production of large-area optical windows. It fully leverages the vacuum baking process of the coating machine and the physical properties of low-melting-point soft metals to achieve direct fabrication of nanomasks without post-annealing. Attached Figure Description

[0019] Figure 1 This is a flowchart of step (iii) of embodiment one of the present invention.

[0020] Figure 2 This is a flowchart of step (four) of embodiment one of the present invention.

[0021] Figure 3 This is a schematic diagram of the spherical nano-metal mask change mechanism in steps (iii) to (iv) of Embodiment 1 of the present invention.

[0022] Figure 4 This is a flowchart of step (five) of embodiment one of the present invention. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings. It should be understood that the specific embodiments described herein are for illustrative purposes only and do not constitute a limitation thereof. In the description of this invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Example 1: Laser window preparation with Sn as the evaporation film material and fused silica as the substrate material.

[0024] This embodiment details the process of fabricating a high-threshold, high-reflection laser window on a fused silica substrate using tin (Sn) as a low-melting-point metal film. The process flow can be found in [reference needed]. Figures 1 to 4 .

[0025] Step S1. Pre-processing and clamping: High-purity (≥99.99%) tin (Sn) particles or blocks are selected as evaporation film materials, and after cleaning, they are placed in the crucible of the electron beam evaporation equipment.

[0026] Take an optical-grade fused silica substrate and clean it sequentially in an ultrasonic cleaner for 15 minutes each with acetone, ethanol, and deionized water to remove surface organic matter and particulate contaminants. After cleaning, dry it with high-purity nitrogen to ensure a clean surface.

[0027] The clean, dry fused silica substrate is fixed on the sample holder inside the vacuum chamber.

[0028] Step S2. Vacuuming and substrate preheating: Pull out and close the vacuum chamber, start the vacuum system, and bring the vacuum to 3*10. -4 Below pa; The heating tube is turned on to heat the vacuum chamber, so that the substrate temperature is controlled at 120°C. This temperature meets a specific range (80°C~200°C as described in this invention) and is lower than the Sn melting point (231.9°C) in order to induce the dehumidification behavior of the subsequently deposited metal film.

[0029] Step S3. Initial deposition to form the initial mask (spherical nanometal mask 1) Electron guns were activated for deposition, with the Sn film thickness controlled to 20 nm. During deposition, at a substrate temperature of 120°C, Sn atoms migrated and aggregated on the substrate surface, forming a preliminary array of spherical nanoparticles (i.e., spherical nanometal mask 1), as shown below. Figure 1 As shown.

[0030] After deposition, the electron gun and heating device are turned off, allowing the sample to cool naturally to room temperature (approximately 25°C) in a vacuum environment. The cooling process helps stabilize the mask structure.

[0031] Step S4. Cyclic deposition to form a high-fill-rate mask (spherical nanometal mask 2) A spherical nanomask 1 was assembled into a vacuum chamber and baked to 120°C. An electron gun was then activated for deposition, achieving a deposition depth of 40 nm. During deposition, newly deposited Sn atoms preferentially adsorb onto existing Sn nanoparticles, promoting their further growth rather than forming new isolated islands. This mechanism is as follows: Figure 3 As shown in the schematic diagram, the size of the nanoparticles is significantly increased and the packing density of the particle distribution is improved through particle merging and growth.

[0032] After deposition, this cycle (two depositions in total) yielded a hundred-nanometer-scale spherical Sn nanoparticle array with more uniform size and significantly improved filling density (i.e., a high-filling-density spherical nanometal mask 2), as shown in Figure 2. Figure 2 As shown. In practical applications, more cycles (such as 3-5 depositions) can be repeated according to the target structure requirements. The temperature and deposition amount in each cycle can be the same or different to achieve precise control of the mask morphology.

[0033] Step S5. Etching to prepare laser window micro / nano structures The fused silica substrate prepared in step S4, covered with the highly filled spherical Sn nanometal mask 2, is removed.

[0034] A 5% hydrofluoric acid (HF) aqueous solution was prepared as the etching solution. The sample was immersed in the etching solution and etched at room temperature. During the etching process, the molten quartz regions not covered by Sn nanoparticles were corroded by the HF solution, while the regions beneath the Sn particles were protected. This "replicated" the morphology of the spherical nanoparticles onto the quartz substrate surface, forming pits or columnar micro / nanostructures with antireflective properties (such as...). Figure 4 (As shown).

[0035] Dry etching can also be performed using ion beam etching (IBE). The sample is placed in the vacuum chamber of an ion beam etching machine, and an argon ion beam is used to bombard the sample surface at a specific energy and incident angle to achieve anisotropic etching, which can also transfer the mask morphology to the substrate.

[0036] Step S6. Mask removal and post-cleaning After etching, the sample surface will have residual Sn mask and possible etching byproducts.

[0037] Preparation of cleaning solution: Mix 20% (w / w) aqueous solution of oxalic acid (H2C2O4) with 10 mol / L aqueous solution of hydrochloric acid (HCl) at a volume ratio of 1:1.

[0038] The laser window sample etched in step S5 was immersed in the cleaning solution and treated at room temperature for 20 minutes. This mixed acid solution can effectively dissolve and remove residual Sn metal and its oxides.

[0039] Remove the laser window, rinse it with deionized water for 10 minutes, and then dry it with high-purity nitrogen.

[0040] Example 2: Fabrication of a laser window using Bi as the film material and BK7 glass as the substrate The main difference between this embodiment and Embodiment 1 lies in the film material and substrate material, as well as the corresponding fine-tuning of process parameters.

[0041] Materials: The evaporation film material is bismuth (Bi, melting point 271.4℃), and the substrate is BK7 optical glass.

[0042] Deposition parameters: Vacuum requirements are the same as in Example 1. The substrate preheating temperature is set to 180°C (still within the 80-200°C range and below the Bi melting point). The initial Bi deposition thickness is 15 nm. After cooling, a second deposition cycle is performed at 180°C with a deposition thickness of 35 nm. A third deposition cycle may also be considered.

[0043] Etching: For BK7 glass, wet etching can be performed using diluted HF buffered etching solution (such as BOE) or acid solution with a specific ratio. Ion beam etching can also be used. Specific parameters need to be optimized through experiments.

[0044] Cleaning: The cleaning solution for removing the Bi mask can still be a mixture of oxalic acid and hydrochloric acid. The concentration and treatment time can be adjusted slightly according to the actual situation.

[0045] Example 3: Fabrication of a laser window using In as the film material and K9 glass as the substrate This embodiment provides an alternative implementation scheme using a different combination of materials.

[0046] Materials: The evaporation film material is indium (In, melting point 156.6℃), and the substrate is K9 optical glass.

[0047] Deposition parameters: Vacuum requirements were the same. Considering the low melting point of In, the substrate preheating temperature was set to 100℃. Three-cycle deposition was used: 10 nm in the first deposition, 30 nm in the second, and 25 nm in the third. After each deposition, the substrate was cooled to room temperature before the next cycle was performed to observe structural evolution.

[0048] Etching and Cleaning: The etching process is the same as in Example 1, with adjustments made to the etching solution composition or etching time for K9 glass. The cleaning steps are similar to those in Example 1, using a mixed acid solution to remove the In mask.

[0049] The performance of the laser window prepared in the above embodiments was tested: Optical performance: The transmittance at a specific laser wavelength (e.g., 1064 nm) was measured using a spectrophotometer. The example products showed that the transmittance at 1064 nm was significantly higher than that of the untreated substrate, reaching over 99%, achieving highly efficient anti-reflection.

[0050] Laser damage threshold: The laser damage threshold (LIDT) was tested according to the ISO standard. The results showed that the LIDT value of the window prepared by this invention was more than an order of magnitude higher than that of the traditional multilayer antireflection film window, exhibiting excellent high threshold characteristics.

[0051] Surface properties: The water contact angles were measured and found to be greater than 150°, exhibiting superhydrophobic properties and confirming its good self-cleaning ability.

[0052] Structural characterization: The micro- and nanostructures on the window surface were observed by scanning electron microscopy (SEM), revealing a periodic or quasi-periodic structure with high uniformity and high filling density, consistent with the morphology of the designed spherical nanomask.

[0053] This invention utilizes conventional electron beam evaporation coating equipment, combined with controllable substrate heating, to achieve a one-step in-situ self-assembly and cyclic growth of low-melting-point soft metal nanomasks. The entire process requires no expensive precious metal targets, no separate high-temperature annealing furnace, and no complex processes. The steps are simple, the parameters are highly controllable, and the repeatability is good, making it particularly suitable for large-area, batch manufacturing of high-performance laser windows.

[0054] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for manufacturing a high-threshold, high-reflection laser window, characterized in that, Includes the following steps: Step (1) Mask preparation: Use a low melting point soft metal with a melting point below 280℃ as the evaporation film material, and put the cleaned optical substrate into the vacuum chamber; Step (2) Cyclic deposition of self-assembled mask: In the vacuum chamber, the optical substrate is heated and maintained at a first specific temperature, which is in the range of 80°C to 200°C and is lower than the melting point of the selected low-melting-point soft metal; using electron beam evaporation technology, the low-melting-point soft metal is deposited on the heated substrate surface at a first deposition amount, and the deposited metal spontaneously agglomerates at the first specific temperature through a dehumidification effect to form an initial spherical nano-metal particle array; the electron beam evaporation deposition process is cyclically executed at least twice, and in at least one subsequent cycle, the substrate is reheated and maintained at a second specific temperature, which is in the range of 80°C to 200°C and is lower than the melting point of the selected low-melting-point soft metal, and then the low-melting-point soft metal is deposited again at a second deposition amount, so that the metal particles continue to grow on the basis of the original array, thereby obtaining a spherical nano-metal mask with high filling degree, wherein the first deposition amount and the second deposition amount are 10nm to 100nm respectively; Step (3) Window structure etching: Using the spherical nano metal mask obtained in step (2) above as a protective layer, the substrate is etched to transfer the morphology of the mask to the substrate surface and form the micro-nano structure of the laser window surface. Step (4) Post-processing cleaning: Remove the mask material and etching products remaining on the surface of the window after etching, clean and dry to obtain the high threshold and high transmittance laser window.

2. The method for manufacturing a high-threshold, high-reflection laser window according to claim 1, characterized in that: In step (1), the low melting point soft metal is a metal with a melting point below 280°C, ductility, and is non-toxic and harmless. The metal is selected from any one of Sn, Bi, and ln.

3. The method for manufacturing a high-threshold, high-reflection laser window according to claim 1, characterized in that: In step (1), the optical substrate is selected from any one of BK7, fused silica, SF5, LAK14, and K9 glass.

4. The method for manufacturing a high-threshold, high-reflection laser window according to claim 1, characterized in that: In step (2), the first specific temperature is the same as or different from the second specific temperature, and / or the first deposition amount is the same as or different from the second deposition amount.

5. The method for manufacturing a high-threshold, high-reflection laser window according to claim 1, characterized in that: In step (2), the cycle is executed at least twice, including 2, 3, 4 or 5 times, and the total number of cycles is N, so that a spherical nano metal mask is obtained after N deposition growths.

6. The method for manufacturing a high-threshold, high-reflection laser window according to claim 1, characterized in that: In step (3), the etching process is either wet chemical etching or dry physical etching.

7. The method for manufacturing a high-threshold, high-reflection laser window according to claim 6, characterized in that: The wet chemical etching is hydrofluoric acid etching, and the dry physical etching is ion beam etching.

8. The method for manufacturing a high-threshold, high-reflection laser window according to claim 1, characterized in that: Step (4) Cleaning steps are as follows: (1) Immerse the laser window in a mixed solution of oxalate and acid for 60 minutes, wherein the oxalate concentration is 5-30%. The acid solution concentration is 5-20 mol / L, and the volume mixing ratio is 1:

1. (2) Take out the sample, rinse it with deionized water for 10 minutes, and blow it dry with high-purity nitrogen.

9. A laser window, characterized in that, It is manufactured by the method according to any one of claims 1 to 8.

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