Preparation method of porous full SiO2 laser reflection film

Abstract

The invention relates to a preparation method of a porous full SiO2 laser reflection film, which comprises the following steps: firstly, alternately depositing SiO2 film layers and SiO2-Al2O3 mixture film layers on a substrate to form a mixture multilayer film; then, etching the prepared mixture multilayer film by using an acid solution to form a porous full SiO2 laser reflection film; and finally, cleaning the porous full SiO2 laser reflection film and naturally airing the porous full SiO2 laser reflection film. The high-refractive-index material layer in the porous full SiO2 laser reflection film prepared by the method is the SiO2 film layer, and the low-refractive-index material layer is the porous SiO2 film layer formed by etching the SiO2-Al2O3 mixture film layer by the acid solution, so that the problem of film layer cracking of the porous full SiO2 laser reflection film can be avoided, the absorption of the film can be greatly reduced, the laser damage threshold of the film can be improved, and the service life of the film can be prolonged. The method has the characteristics of simplicity in operation, low cost and wide application range, and can be used for preparing different types and different sizes of laser films such as light splitting films and antireflection films.

Description

Technical Field

[0001] The present invention relates to the field of optical films, in particular to a method for preparing a porous all-SiO2 laser reflective film. Background Art

[0002] Thin-film components play a crucial role in laser systems. Optical thin-film components in laser systems not only need to meet specific spectral performance requirements but also exhibit a high laser damage threshold (LDT). Traditional laser reflective films are fabricated by alternating deposition of high- and low-refractive-index coating materials. The optical band gap of the high-refractive-index material is smaller than that of the low-refractive-index material, and therefore often exhibits a lower intrinsic laser damage threshold (LDT). This LDT is limited by the limited number of coating materials available in nature. Ultra-low-loss SiO2 is an indispensable coating material for the fabrication of laser thin films from the ultraviolet to near-infrared wavelengths. Its refractive index in the visible wavelength range is approximately 1.44, depending on the coating process parameters used, but the tunable range of the deposition process is limited. If SiO2 materials with varying refractive indices can be prepared using appropriate processes and used in the fabrication of laser reflective films, the LDT of these films could be improved. Currently, the main approaches for increasing the refractive index control range of SiO2 films include tilted deposition, sol-gel, and etching. The oblique deposition method can produce SiO2 films with varying refractive indices by varying the deposition angle. However, this method inherently suffers from poor film uniformity due to varying geometric conditions at different locations on the substrate. Currently, relatively good uniformity can only be achieved within a diameter of a few centimeters, making it unsuitable for the preparation of larger optical thin-film components. The sol-gel method is a common method for producing anti-reflection films, but interpenetration of the sol between layers and cracking are unavoidable when producing films with a large number of layers, making it unsuitable for the preparation of laser-reflective films. Etching methods primarily include those based on nanolaminates and those based on mixtures. The nanolaminate-based etching method removes a sublayer of a component within the nanolaminate by acid etching, resulting in porous SiO2 films with lower refractive indices. However, this method suffers from significant thickness variation before and after etching and low structural strength after etching. The mixture-based etching method can address this significant thickness variation and produce porous SiO2 films with lower refractive indices. However, this method is only suitable for producing single- or double-layer anti-reflection films with relatively small thicknesses. Currently, the thickness of porous SiO2 films prepared by etching methods has been reported to be less than 200nm (DE102016100914B4; ACS Appl. NanoMater. 2023, 6, 15437-15444; Nano Lett. 2022, 22, 7358-7362). Further increases in the thickness of porous SiO2 films can lead to cracking. Laser reflective films can be several microns thick, making them difficult to prepare using etching methods, and no relevant reports have been published. Summary of the Invention

[0003] The present invention aims to overcome the shortcomings of the prior art by providing a method for preparing a porous all-SiO2 laser reflective film. First, a multilayered SiO2 film and a SiO2-Al2O3 mixture film are alternately deposited to form the mixture. The prepared multilayered film is then etched with an acid solution to form a porous all-SiO2 laser reflective film. Finally, the film is cleaned and dried, resulting in a porous all-SiO2 laser reflective film with an intact surface and a high damage threshold.

[0004] The technical solutions of the present invention are as follows:

[0005] A method for preparing a porous all-SiO2 laser reflective film is characterized in that it includes: first, alternately depositing SiO2 film layers and SiO2-Al2O3 mixture film layers on a substrate to form a mixture multilayer film; then, etching the mixture multilayer film with an acid solution to form a porous all-SiO2 laser reflective film consisting of alternating SiO2 film layers and porous SiO2 film layers; and finally, cleaning and drying.

[0006] According to the preparation method of the above-mentioned porous all-SiO2 laser reflective film, its characteristics are that the SiO2 film layer and the SiO2-Al2O3 mixture film layer can be deposited by electron beam co-evaporation, ion beam assisted electron beam co-evaporation and other technologies; the deposition rates of SiO2 and Al2O3 are controlled by the quartz crystal oscillation method, thereby controlling the proportion of Al2O3 in the SiO2-Al2O3 mixture film layer; the thickness of the SiO2-Al2O3 mixture film layer is controlled by optical monitoring method or quartz crystal oscillation method.

[0007] According to the preparation method of the above-mentioned porous all-SiO2 laser reflective film, its characteristic is that the high refractive index material layer in the porous all-SiO2 laser reflective film is a SiO2 film layer, and the low refractive index material layer is a porous SiO2 film layer formed by etching a SiO2-Al2O3 mixture film layer with an acid solution.

[0008] According to the method for preparing the porous all-SiO2 laser reflective film, the feature is that the acid solution is a H2SO4, HCl or HNO3 solution or a mixed solution thereof with a mass fraction of not less than 5%.

[0009] According to the above-mentioned method for preparing the porous all-SiO2 laser reflective film, its characteristic is that the time for etching the mixture multilayer film with the acid solution is not less than 12 hours.

[0010] According to the preparation method of the above-mentioned porous all-SiO2 laser reflective film, its characteristic is that the cleaning and drying are specifically to rinse the porous all-SiO2 laser reflective film with deionized water for not less than 1 minute and soak it in anhydrous ethanol for not less than 5 minutes and then dry it naturally.

[0011] According to the method for preparing the porous all-SiO2 laser reflective film, its characteristic is that the substrate is K9 glass or fused quartz.

[0012] Technical effects of the present invention:

[0013] 1. The method of the present invention utilizes the SiO2 film layer as the high refractive index layer and the porous SiO2 film layer formed by etching the SiO2-Al2O3 mixture film layer with an acid solution as the low refractive index layer, which can avoid the film cracking problem of the porous all-SiO2 laser reflective film.

[0014] 2. The present invention prepares a porous all-SiO2 laser reflective film by acid etching a mixture multilayer film composed of a conventional SiO2 film layer and a SiO2-Al2O3 mixture film layer, which can greatly reduce the absorption of thin film components.

[0015] 3. The method of the present invention prepares a porous all-SiO2 laser reflective film, which can meet the spectral performance requirements of the laser reflective film while realizing the high damage threshold requirements of the thin film element.

[0016] 4. The present invention is simple to operate, low in cost, and suitable for large-sized components. Through appropriate film structure design, it is also suitable for the preparation of laser films such as beam splitting films and anti-reflection films. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a flow chart for preparing the porous all-SiO2 laser reflective film of the present invention, wherein (a) is a mixture multilayer film and (b) is a porous all-SiO2 laser reflective film.

[0018] Figure 2 This is a reflection spectrum diagram of the porous all-SiO2 laser reflective film prepared in Example 1 of the present invention.

[0019] Figure 3 The absorption of the non-acid-etched mixture multilayer film prepared in Example 1 of the present invention, the porous all-SiO2 laser reflective film obtained by acid etching, and the fused silica substrate changes with time under 355nm laser irradiation.

[0020] Figure 4 This is a probability distribution diagram of 355nm single-pulse laser-induced damage of the porous all-SiO2 laser reflective film prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0021] The present invention will be further described below with reference to the embodiments and drawings, but the scope of protection of the present invention should not be limited thereto.

[0022] Example 1:

[0023] The method for preparing a porous all-SiO2 laser reflective film is as follows:

[0024] ① Substrate cleaning: Use deionized water to ultrasonically clean the fused quartz substrate to remove contaminants on the substrate surface;

[0025] ②Multilayer film deposition: Ion beam assisted electron beam co-evaporation deposition is used to alternately deposit conventional SiO2 film layers and SiO2-Al2O3 mixture film layers on the substrate surface to form a mixture multilayer film. The film system structure is designed as follows: Substrate / 2L1 (L2M) 25 L2 / Air, where Substrate represents a fused silica substrate and Air represents an incident medium of air. L1 represents a SiO2 layer with a physical thickness of 69.0 nm deposited by electron beam evaporation (deposition rate of 0.2 nm / s), L2 represents a conventional SiO2 layer with a physical thickness of 69.0 nm deposited by plasma-assisted electron beam evaporation (deposition rate of 0.4 nm / s, plasma source bias of 90 V), and M represents an Al2O3-SiO2 mixture layer with a physical thickness of 85.2 nm deposited by plasma-assisted electron beam evaporation (the deposition rates of Al2O3 and SiO2 in M are 0.14 nm / s and 0.10 nm / s, respectively, and the plasma source bias is 100 V). The schematic diagram of the structure of the mixture multilayer film is shown in FIG. Figure 1 (a).

[0026] ③ Acid etching: At room temperature, the prepared mixture multilayer film sample was etched with 36% H2SO4 by mass for 36 hours to obtain a porous all-SiO2 laser reflective film. The structural diagram is shown in the figure. Figure 1 (b).

[0027] ④ Cleaning: Rinse the sample with deionized water for 1 minute, soak the sample in anhydrous ethanol for 5 minutes, take it out, and dry it naturally.

[0028] The prepared porous all-SiO2 laser reflective film has a good surface structure and no cracks.

[0029] Spectral performance measurements:

[0030] Spectral measurements of the porous all-SiO2 laser reflective film prepared by the present invention were performed using a Lambda 1050 spectrophotometer. The incident angle was 38°, the s-polarization component was used, and the measurement wavelength range was 300 nm to 450 nm. The measured quantity was transmittance. The reflectance value was calculated by subtracting the transmittance value from 100%. Figure 2This is a reflection spectrum diagram of the porous all-SiO2 laser reflection film prepared by the present invention. When the incident angle is 38 degrees, the reflectivity at 355nm is 99.4%.

[0031] Absorption measurements:

[0032] The absorption of the non-acid-etched mixed multilayer film sample and the acid-etched porous all-SiO2 laser reflective film sample was tested using an optical thin film weak absorption measuring instrument based on the thermal lens effect. The test wavelength was 355 nm. Figure 3 The absorption of a non-acid-etched mixed multilayer film, a porous all-SiO2 laser-reflective film obtained by acid etching, and a fused silica substrate prepared using the present method over time under 355nm laser irradiation is shown. The absorption of the prepared porous all-SiO2 laser-reflective film is approximately 10 ppm, close to the level of the fused silica substrate.

[0033] Laser damage threshold measurement:

[0034] According to the ISO 21254 test standard, the porous all-SiO2 laser reflective film prepared by the method of the present invention was tested using a 1-on-1 test method. Laser wavelength: 355nm, pulse width: 8ns, incident angle: 38°, spot area: 0.22mm 2 , polarization state: s component. Test results show that the porous all-SiO2 laser reflective film prepared by the method of the present invention has a high laser damage threshold, which can reach 12.3J / cm at a wavelength of 355nm. 2 . Figure 4 This is a probability distribution diagram of laser damage of the porous all-SiO2 laser reflective film prepared by the method of the present invention.

[0035] Example 2:

[0036] When the 36% by mass H2SO4 in Example 1 is replaced with 36% by mass HNO3 for etching experiments, similar results can be obtained.

Claims

1. A method for preparing a porous all-SiO2 laser reflective film, characterized in that: include: First, SiO2 film layers and SiO2-Al2O3 mixture film layers are alternately deposited on a substrate to form a mixture multilayer film; then, the mixture multilayer film is etched using an acid solution to form a porous all-SiO2 laser reflective film consisting of alternating SiO2 film layers and porous SiO2 film layers; finally, the film is cleaned and dried.

2. The method for preparing a porous all-SiO2 laser reflective film according to claim 1, characterized in that: The SiO2 film layer and the SiO2-Al2O3 mixture film layer can be deposited by techniques such as electron beam co-evaporation and ion beam assisted electron beam co-evaporation; the deposition rates of SiO2 and Al2O3 are controlled by a quartz crystal oscillation method, thereby controlling the proportion of Al2O3 in the SiO2-Al2O3 mixture film layer; the thickness of the SiO2-Al2O3 mixture film layer is controlled by an optical monitoring method or a quartz crystal oscillation method.

3. The method for preparing a porous all-SiO2 laser reflective film according to claim 1, characterized in that: The high refractive index material layer in the porous all-SiO2 laser reflective film is a SiO2 film layer, and the low refractive index material layer is a porous SiO2 film layer formed by etching a SiO2-Al2O3 mixture film layer with an acid solution.

4. The method for preparing a porous all-SiO2 laser reflective film according to claim 1, characterized in that: The acid solution is an H2SO4, HCl or HNO3 solution or a mixed solution thereof with a mass fraction of not less than 5%.

5. The method for preparing a porous all-SiO2 laser reflective film according to claim 1, characterized in that: The time for etching the mixture multilayer film with the acid solution is not less than 12 hours.

6. The method for preparing a porous all-SiO2 laser reflective film according to claim 1, characterized in that: The cleaning and drying is specifically to rinse the porous all-SiO2 laser reflective film with deionized water for not less than 1 minute and soak it in anhydrous ethanol for not less than 5 minutes and then dry it naturally.

7. The method for preparing a porous all-SiO2 laser reflective film according to claim 1, characterized in that: The substrate is K9 glass or fused quartz.

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