High damage threshold laser reflective film based on graded optical band gap high refractive index material and preparation method thereof

Abstract

High-damage-threshold laser reflection film based on graded optical band gap high refractive index material and preparation method thereof, along the direction from the substrate to the surface of the film layer, the nano-laminated material or mixed material with gradually increased optical band gap is used as the high refractive index material layer, which replaces the high refractive index material layer with fixed optical band gap in the conventional laser reflection film. Among them, the optical band gap of the nano-laminated material is realized by adjusting the thickness ratio of the sub-layer material, and the optical band gap of the mixed material is realized by adjusting the mixing ratio of the material. In the high electric field intensity area, the high refractive index material layer with larger optical band gap is used, and in the low electric field intensity area, the high refractive index material layer with larger refractive index is used, which can significantly improve the damage threshold of the laser reflection film, and does not significantly affect the optical performance and mechanical performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of optical thin films, and particularly relates to a high-damage-threshold laser reflection thin film based on a gradient optical bandgap high-refractive material and a preparation method thereof. BACKGROUND

[0002] High-power laser systems have important applications in the fields of inertial confinement fusion, high-energy density physics and material science. Laser reflection thin films are core components in high-power laser systems, and improving their laser-induced damage threshold is an important factor for increasing the output power of laser systems. Laser damage of reflection thin films is closely related to the coating material, film system design, thin film deposition process, and post-processing technology. Among them, optimizing the selection of coating materials and the design of film system structure are important ways to improve the damage threshold of laser reflection thin films. Traditional laser mirrors are prepared by alternately depositing high-refractive materials and low-refractive materials. For example, for near-infrared waveband laser reflection thin films, silicon dioxide (SiO2) is almost irreplaceable as a low-refractive material with ultra-low loss, and common high-refractive materials include titanium dioxide (TiO2), tantalum pentoxide (Ta2O5) and hafnium dioxide (HfO2). HfO2 has a relatively larger optical bandgap, which helps to obtain a higher laser damage threshold, and is the most commonly used high-refractive material. However, laser reflection thin films based on HfO2 materials as high-refractive layers gradually cannot meet the increasing laser power demand of laser systems. At present, there are mainly two methods to improve the laser damage threshold:

[0003] One is to replace pure HfO2 material with mixed material or laminated material as high-refractive layer. For example, researchers use Al2O3-HfO2 mixed material and Al2O3 / HfO2 laminated material to improve the laser damage threshold to a certain extent

Optics & Laser Technology 171, 110466, 2024; Optical Materials Express 13(3), 667-677, 2023

[0004] The second is to use laser pretreatment or heat annealing and other post-processing methods to reduce the density of absorption defects in the thin film, thereby improving the laser damage threshold

Applied Surface Science 579, 152192, 2022;‌ Optical Materials Express 15(7), 1467-1482, 2025

[0005] To overcome the shortcomings of the prior art, this invention proposes a high-damage-threshold laser-reflective thin film based on a graded-gap high-refractive-index material and its preparation method. The method employs a nano-layered material or a hybrid material with a gradually increasing optical bandgap along the direction from the substrate to the film surface as the high-refractive-index material layer, replacing the high-refractive-index material layer with a fixed optical bandgap in conventional laser-reflective thin films. Specifically, the optical bandgap of the nano-layered material is achieved by adjusting the thickness ratio of the sublayer materials, while the optical bandgap of the hybrid material is achieved by adjusting the material mixing ratio. This invention uses a high-refractive-index material layer with a larger optical bandgap in the high electric field intensity region and a high-refractive-index material layer with a larger refractive index in the low electric field intensity region, which can significantly improve the damage threshold of the laser-reflective thin film without significantly affecting its optical and mechanical properties.

[0006] The technical solution of the present invention is as follows:

[0007] High-damage-threshold laser-reflective thin films based on graded-gap high-refractive-index materials are characterized by their substrate-like structure. k LH1LH2L……H N L(YL) m j L|air; where substrate is the base material; air is air; L is a low-refractive-index material layer; H i This is a high-refractive-index material layer with a graded optical bandgap, where the optical bandgap gradually increases from the substrate towards the film surface. i=1, 2, 3...N Y represents a high-refractive-index material layer with a fixed optical bandgap. m It is the number of periods, and m ≥0; k and j The coefficient is 0 ≤ k≤ 8, j The value of makes the electric field at the air-film interface zero.

[0008] The aforementioned graded optical bandgap high refractive index material layer is a nano-layered material or a hybrid material, consisting of material H CH and material H CL composition.

[0009] The optical bandgap of the aforementioned nanolayered materials is achieved by adjusting the thickness ratio of the sublayer materials, and the optical bandgap of the aforementioned hybrid materials is achieved by adjusting the material mixing ratio.

[0010] If the graded optical bandgap high refractive index material layer H i The layer uses a nano-layered material, and its structure is as follows: B , among which, sub-layer thickness and sub-layer thickness Satisfy the following formula:

[0011]

[0012]

[0013] In the formula, For material H CH refractive index, For material H CL refractive index, N This represents the total number of layers in a graded optical bandgap high refractive index material. B Let be the number of sub-layer periods, and B >0, λ This is the reference wavelength.

[0014] If the graded optical bandgap high refractive index material layer H i The layer uses a hybrid material, the component material H CL and H CH Mixing ratio Satisfy the following formula:

[0015]

[0016] In the formula, For material H CH refractive index, For material H CL refractive index, For H i The refractive index of the layer.

[0017] The above-mentioned graded optical bandgap high refractive index material layer H i The refractive index of the layer Satisfy the following formula:

[0018]

[0019] The aforementioned low-refractive-index material layer L is SiO2; the aforementioned high-refractive-index material layer Y with a fixed optical bandgap is H, which is a component of a nano-layered material or a hybrid material. CL Material.

[0020] The aforementioned nano-layered materials are Al2O3 / HfO2 layered materials, Al2O3 / Ta2O5 layered materials, or SiO2 / HfO2 layered materials, etc.

[0021] The aforementioned mixed materials are Al2O3-HfO2 mixed materials, Al2O3-Ta2O5 mixed materials, or SiO2-HfO2 mixed materials, etc.

[0022] A method for preparing a high-damage-threshold laser-reflective thin film based on a graded-gap high-refractive-index material, characterized in that the method includes the following steps:

[0023] S1. Parameter Input: Includes reference wavelength λ The refractive index of the substrate Two materials H that make up nanolayered or hybrid materials CH and H CL refractive index and The refractive index of the low refractive index material layer L ,in, Graded optical bandgap high refractive index material layer H i Total number of layers N The refractive index of the Y layer, a high-refractive-index material with a fixed optical bandgap. and number of cycles m ;

[0024] S2. Membrane system design:

[0025] 1) Calculate H for each graded optical bandgap high refractive index material layer i The refractive index of the layer ;

[0026] 2) When the graded optical bandgap high refractive index material layer uses a nano-layered material, calculate H. i Sublayer thickness and sub-layer thickness Set the number of sub-layer cycles, B.

[0027] When the graded optical bandgap high refractive index material layer uses a hybrid material, the calculation of H... i Layer component material H CL With component material H CH Mixing ratio H was calculated according to conventional optical thin film design methods. i The thickness of the film layer;

[0028] 3) The film thickness of the remaining layers in the film system structure was calculated using conventional optical thin film design methods;

[0029] 4) Set coefficients k and j ;

[0030] 5) Output membrane structure: substrate| k LH1LH2L……H N L(YL) m j L|air;

[0031] S3. Substrate cleaning and clamping: after cleaning and drying the substrate, clamp it into the fixture of the film coating equipment;

[0032] S4. Thin film preparation: heat the substrate to 100-230℃; when the vacuum degree is better than 9.0x10 -3 Pa, deposit multiple layers of film on the substrate according to the film system design structure until the last layer of thin film.

[0033] The above multiple layers of film are prepared by electron beam co-evaporation, ion beam co-sputtering or atomic layer deposition.

[0034] The mixing ratio of the above mixed materials By adjusting the deposition rate of component material H CL and component material H CH .

[0035] Technical effects of the present application:

[0036] 1. The present application uses nanolayer materials or mixed materials with gradually increasing optical band gap as high refractive index material layers in the direction from the substrate to the surface of the film layer, replacing the high refractive index material layer with fixed optical band gap in the conventional laser reflection film. The peak value of electric field intensity in the dielectric reflection film with regular film system structure gradually increases in the direction from the substrate to the surface of the film. On the one hand, using materials with larger optical band gap in the area with higher electric field intensity can improve the laser damage threshold of the laser reflection film; on the other hand, materials with smaller optical band gap often have larger refractive index, and using high refractive index materials with relatively smaller optical band gap in the area with lower electric field intensity can increase the reflectivity and reflection bandwidth of the laser reflection film.

[0037] 2. The high refractive index material layer with gradually increasing optical band gap can use nanolayer materials or mixed materials, and the film coating equipment that cannot simultaneously deposit two materials can also use nanolayer materials to achieve the effect of the present application, improving the applicability of the film preparation equipment. At the same time, the optical band gap of nanolayer materials is realized by adjusting the thickness ratio of sublayer materials, and the optical band gap of mixed materials is realized by adjusting the mixing ratio of materials, increasing the flexibility of film design and preparation.

[0038] 3. The present application can significantly improve the damage threshold of the laser reflection film without significantly affecting the optical and mechanical properties of the laser reflection film.

[0039] 4. The present application is very suitable for the preparation of short pulse strong laser film elements. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1This is a schematic diagram of the film structure of the high damage threshold laser reflective thin film based on a high refractive index material with a graded optical bandgap according to the present invention.

[0041] Figure 2 The diagram shows the laser damage probability distribution of the high-refractive-index material laser-reflecting thin film with graded optical bandgap prepared in Example 1 of the present invention and the conventional high-refractive-index material laser-reflecting thin film with fixed optical bandgap prepared in the comparative example. Detailed Implementation

[0042] The present invention will be further described below with reference to embodiments and accompanying drawings, but this should not be construed as limiting the scope of protection of the present invention. Please refer to [the accompanying drawings first]. Figure 1 , Figure 1 This is a schematic diagram of the film structure of the high damage threshold laser reflective thin film based on a high refractive index material with a graded optical bandgap according to the present invention.

[0043] Example 1

[0044] Using Al2O3 / HfO2 stacked material as the high-refractive-index material and SiO2 as the low-refractive-index material, a laser-reflective thin film with a reflectivity higher than 99.5% at 1053 nm was designed and fabricated. Optical bandgap tuning of the high-refractive-index material layer was achieved by changing the ratio of Al2O3 to HfO2 sublayer thicknesses in the Al2O3 / HfO2 stacked material. The steps are as follows:

[0045] ① Input parameters: including reference wavelength 1207nm, substrate refractive index 1.52, refractive indices of HfO2 sublayer material and Al2O3 sublayer material composed of Al2O3 / HfO2 nanolayer material are 1.891 and 1.602 respectively, refractive index of low refractive index material layer SiO2 layer is 1.452, number of sublayer periods is 4, number of layers of high refractive index material layer with graded optical band gap is 11, number of layers of high refractive index material layer Al2O3 with fixed optical band gap is 5, that is, number of periods m=5, refractive index of Al2O3 layer is 1.602;

[0046] ② Calculate the first according to formula (1) i layer( i =1, 2, 3...11) High-refractive-index material layer H with graded optical bandgap i The refractive index of the layer :

[0047] (1)

[0048] ③ Gradient optical bandgap high refractive index material layer H i layer( i =1, 2, 3...11) is a structure with [ 4 Nanoscale stacked materials, sublayer The material of the layer H is HfO2, the refractive index is 1.891, and the thickness of the sub-layer H1 is calculated according to formula (2) The material of the layer H is HfO2, the refractive index is 1.891, and the thickness of the sub-layer H1 is calculated according to formula (2) The thickness of the layer HfO2 The thickness of the sub-layer H1 is calculated according to formula (3) The thickness of the layer Al2O3 :

[0049] (2)

[0050] (3)

[0051] The thickness of the sub-layer H1 is calculated according to formula (3) i The thickness of the sub-layer material in the layer H is as follows.

[0052] Table 1 The layer H of the graded optical bandgap high refractive index material in Example 1 i The thickness of the sub-layer material in the layer H

[0053]

[0054] (4) The computer outputs the film system structure: Substrate | 2LH1LH2L …… H 10 LH 11 L (YL) 5 3.15L | air; wherein the thicknesses of the Y layer and the L layer are 188.4 nm and 207.8 nm, respectively.

[0055] (5) Substrate cleaning and clamping: after the substrate is cleaned and dried, it is clamped into the clamp of the film coating equipment;

[0056] (6) Thin film preparation: heat the substrate to 200℃; when the vacuum degree is better than 9.0×10 -4 Pa, use electron beam evaporation deposition technology to deposit a multilayer film on the substrate according to the film system structure design until the last layer of thin film. The H1, H2, H3 …… H N layers are alternately deposited according to the above structure 4 Al2O3 / HfO2 nanolaminate material.

[0057] Comparative Example

[0058] Using electron beam evaporation deposition technology, a conventional fixed optical bandgap high refractive index material laser reflection thin film with a film system structure of substrate | 2L (ML) 16 3.15L | air is prepared, wherein the high refractive index material layer M is a fixed mixed ratio of 0.69:0.31 Al2O3-HfO2 mixed material, and the low refractive index material layer L is SiO2 material.

[0059] Laser damage threshold measurement:

[0060] According to the ISO 21254 test standard, the laser reflective film prepared by the embodiment 1 and the comparative example is tested for damage threshold by using the 1-on-1 test method. Laser wavelength: 1053 nm, pulse width: 8 ps, incident angle: 56° (sample of embodiment 1) and 50.1° (sample of comparative example), polarization state: s component. The test results show that the laser reflective film prepared by the method of the application has a high laser damage threshold, and the laser damage threshold at 1053 nm wavelength can reach ~ 9.4 J / cm 2 , which is higher than that of the conventional fixed optical bandgap high refractive index material laser reflective film (~ 6.3 J / cm 2 ). Figure 2 The laser damage probability distribution diagram of the gradient optical bandgap high refractive index material laser reflective film prepared by the embodiment 1 of the application and the conventional fixed optical bandgap high refractive index material laser reflective film prepared by the comparative example is shown.

[0061] Embodiment 2

[0062] The Al2O3-HfO2 mixed material is used as the high refractive index material, and the SiO2 is used as the low refractive index material, and the laser reflective film with the reflectivity of 1053 nm higher than 99.5% is designed and prepared. By changing the mixing ratio of the Al2O3 material and the HfO2 material in the Al2O3-HfO2 mixed material, the optical bandgap tuning of the high refractive index material layer is realized.

[0063] In addition to the Al2O3 / HfO2 stacked material and the Al2O3-HfO2 mixed material, the Al2O3 / Ta2O5 stacked material, the SiO2 / HfO2 stacked material, the Al2O3-Ta2O5 mixed material or the SiO2-HfO2 mixed material can also be used as the high refractive index material, and the SiO2 is used as the low refractive index material, and the high damage threshold laser reflective film is designed and prepared. By changing the thickness ratio of the sub-layer material in the nano-stacked material, or the material mixing ratio in the mixed material, the optical bandgap tuning of the high refractive index material layer is realized.

Claims

1. A high-damage-threshold laser-reflective thin film based on a graded-gap high-refractive-index material, characterized in that, The membrane structure is substrate|kLH1LH2L……H N L(YL) m jL|air; where substrate is the basis; air represents air; L represents a low-refractive-index material layer; H represents air. i For a high-refractive-index material layer with a graded optical bandgap, the optical bandgap gradually increases from the substrate to the film surface, i=1,2,3……N; Y is a high-refractive-index material layer with a fixed optical bandgap; m is the number of periods, and m≥0; k and j are coefficients, and 0≤k≤8, the value of j is such that the electric field at the air-film interface is 0; The graded optical bandgap high refractive index material layer is a nano-layered material or a hybrid material, consisting of material H CH and material H CL Composition; Material H CH The refractive index is Material H CL The refractive index is ; If the graded optical bandgap high refractive index material layer H i The layer uses a nano-layered material, and its structure is as follows: B , among which, sub-layer thickness and sub-layer thickness Satisfy the following formula: ； ； In the formula, N is the total number of layers of high refractive index material with graded optical bandgap, B is the number of sub-layer periods, and B>0, and λ is the reference wavelength.

2. The high damage threshold laser reflective thin film based on a graded optical bandgap high refractive index material according to claim 1, characterized in that, The optical bandgap of the nanolayered material is achieved by adjusting the thickness ratio of the sublayer materials, and the optical bandgap of the hybrid material is achieved by adjusting the material mixing ratio.

3. The high damage threshold laser-reflective thin film based on a graded optical bandgap high refractive index material according to claim 1, characterized in that, If the graded optical bandgap high refractive index material layer H i The layer uses a hybrid material, the component material H CL and H CH Mixing ratio Satisfy the following formula: ； In the formula, For H i The refractive index of the layer.

4. The high damage threshold laser reflective thin film based on a graded optical bandgap high refractive index material according to any one of claims 1-3, characterized in that, The graded optical bandgap high refractive index material layer H i The refractive index of the layer Satisfy the following formula: 。 5. The high damage threshold laser reflective thin film based on a graded optical bandgap high refractive index material according to claim 1, characterized in that, The low-refractive-index material layer L is SiO2; the fixed optical bandgap high-refractive-index material layer Y is H, which is a nano-layered material or a hybrid material. CL Material.

6. The high damage threshold laser-reflective thin film based on a graded optical bandgap high refractive index material according to claim 1, characterized in that, The nanolayered material is an Al2O3 / HfO2 layered material, an Al2O3 / Ta2O5 layered material, or a SiO2 / HfO2 layered material.

7. The high damage threshold laser reflective thin film based on a graded optical bandgap high refractive index material according to claim 1, characterized in that, The mixed material is an Al2O3-HfO2 mixed material, an Al2O3-Ta2O5 mixed material, or a SiO2-HfO2 mixed material.

8. A method for preparing a high-damage-threshold laser-reflective thin film based on a graded-gap high-refractive-index material as described in any one of claims 1-7, characterized in that, The method includes the following steps: S1. Parameter Input: Includes reference wavelength λ and substrate refractive index. Two materials H that make up nanolayered or hybrid materials CH and H CL refractive index and The refractive index of the low refractive index material layer L ,in, Graded optical bandgap high refractive index material layer H i The total number of layers N, and the refractive index of the high-refractive-index material layer Y with a fixed optical bandgap. and the number of cycles m; S2. Membrane system design: 1) Calculate H for each graded optical bandgap high refractive index material layer i The refractive index of the layer ; 2) When the graded optical bandgap high refractive index material layer uses a nano-layered material, calculate H. i Sublayer thickness and sub-layer thickness Set the number of sub-layer cycles, B. When the graded optical bandgap high refractive index material layer uses a hybrid material, the calculation of H... i Layer component material H CL With component material H CH Mixing ratio H was calculated according to conventional optical thin film design methods. i The thickness of the film layer; 3) The film thickness of the remaining layers in the film system structure was calculated using conventional optical thin film design methods; 4) Set the coefficients k and j; 5) Output membrane structure: substrate|kLH1LH2L……H N L(YL) m jL|air; S3. Substrate cleaning and clamping: After cleaning and drying the substrate, clamp it into the fixture of the coating equipment; S4. Thin film preparation: Heat the substrate to 100℃~230℃; when the vacuum degree is better than 9.0×10⁻⁶... -3 At Pa, multiple layers of film are deposited on the substrate according to the film system design structure until the last thin film is deposited.

9. The method for preparing a high-damage-threshold laser-reflective thin film based on a graded-gap high-refractive-index material according to claim 8, characterized in that, The multilayer film is prepared by electron beam co-evaporation, ion beam co-sputtering, or atomic layer deposition.

10. The method for preparing a high-damage-threshold laser-reflective thin film based on a graded-gap high-refractive-index material according to claim 8, characterized in that, The mixing ratio of the mixed materials By adjusting the component material H CL With component material H CH The deposition rate was obtained.

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