High-damage-threshold laser reflection film based on gradient optical band gap high-refractive-index material and preparation method of high-damage-threshold laser reflection film

Abstract

According to the high-damage-threshold laser reflection film based on the gradually-changed optical band gap high-refractive-index material and the preparation method of the high-damage-threshold laser reflection film, a nanometer laminated material or a mixed material with the gradually-increased optical band gap is adopted as a high-refractive-index material layer in the direction from a substrate to the surface of a film layer, and the high-refractive-index material layer with the fixed optical band gap in a conventional laser reflection film is replaced. Wherein 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. The high-refractive-index material layer with a larger optical band gap is adopted in the high-electric-field-intensity area, the high-refractive-index material layer with the larger refractive index is adopted in the low-electric-field-intensity area, the damage threshold value of the laser reflection film can be obviously increased, and the optical performance and the mechanical performance of the laser reflection film are not obviously affected.

Description

Technical Field

[0001] The present invention relates to the technical field of optical films, in particular to a high damage threshold laser reflective film based on a graded optical band gap high refractive index material and a preparation method thereof. Background Art

[0002] High-power laser systems have important applications in fields such as inertial confinement fusion, high-energy-density physics, and materials science. Laser reflective films are core components in high-power laser systems, and improving their laser-induced damage threshold (LIDT) is crucial for increasing the output power of laser systems. Laser damage to reflective films is closely related to the coating material, film system design, film deposition process, and post-processing techniques. Optimizing the selection of coating materials and the design of film systems is a key approach to improving the damage threshold of laser reflective films. Traditional laser reflectors are fabricated by alternating deposition of high-refractive-index and low-refractive-index materials. For example, for laser reflective films operating in the near-infrared band, ultra-low-loss silicon dioxide (SiO2) is an almost irreplaceable low-refractive-index material. Commonly used high-refractive-index materials include titanium dioxide (TiO2), tantalum pentoxide (Ta2O5), and hafnium dioxide (HfO2). HfO2, with its relatively large optical bandgap, facilitates a higher LDT and is therefore the most commonly used high-refractive-index material. However, laser reflective films based on HfO2 as the high-refractive-index layer are increasingly unable to meet the ever-increasing laser power demands of laser systems. Currently, there are two main methods to improve the laser damage threshold: One is to use mixed materials or stacked materials instead of pure HfO2 materials as high refractive index layers. For example, researchers used Al2O3-HfO2 mixed materials and Al2O3 / HfO2 stacked materials to improve the laser damage threshold to a certain extent. Optics & Laser Technology 171,110466,2024; Optical Materials Express 13(3), 667-677, 2023]. However, in order to take into account both the reflection bandwidth and the laser damage threshold of the laser reflective film, the Al2O3 ratio of the mixed material or nano-laminated material is limited, which also limits the further improvement of the laser damage threshold.

[0003] The second is to use post-processing methods such as laser pretreatment or thermal annealing to reduce the density of absorption defects in the film, thereby increasing the laser damage threshold. Applied Surface Science 579, 152192, 2022;‌ Optical Materials Express 15(7), 1467-1482, 2025]. However, for thin film components with excellent preparation technology, the effect of post-processing methods on improving the laser damage threshold is very limited, and it increases the preparation process and cost. Summary of the Invention

[0004] In order to overcome the deficiencies of the above-mentioned prior art, the present invention proposes a high damage threshold laser reflective film based on a high refractive index material with a gradient optical band gap and a preparation method thereof. The method of the present invention adopts a nano-laminated material or a mixed material with a gradually increasing optical band gap as a high refractive index material layer along the direction from the substrate to the surface of the film layer, replacing the high refractive index material layer with a fixed optical band gap in the conventional laser reflective film. The optical band gap of the nano-laminated material is achieved by adjusting the thickness ratio of the sub-layer materials, and the optical band gap of the mixed material is achieved by adjusting the material mixing ratio. The present invention adopts a high refractive index material layer with a larger optical band gap in the high electric field intensity area and a high refractive index material layer with a larger refractive index in the low electric field intensity area, which can significantly improve the damage threshold of the laser reflective film without significantly affecting its optical and mechanical properties.

[0005] The technical solutions of the present invention are as follows: The high damage threshold laser reflective film based on the graded optical band gap high refractive index material is characterized in that the film structure is substrate| k LH1LH2L……H N L(YL) m j L|air; substrate is the substrate; air is air; L is the low refractive index material layer; H i It is a gradient optical band gap high refractive index material layer, whose optical band gap gradually increases from the substrate to the film surface. i=1,2,3……N ; Y is a layer of high refractive index material with a fixed optical band gap; m is the number of cycles, and m ≥0; k and j is the coefficient, and 0≤ k≤ 8, j The value of makes the electric field at the interface between air and film layer equal to 0.

[0006] The above-mentioned gradient optical band gap high refractive index material layer is a nano-laminated material or a mixed material, which is composed of material H CH and material H CL composition.

[0007] The optical band gap of the above-mentioned nano-laminated material is achieved by adjusting the thickness ratio of the sub-layer materials, and the optical band gap of the above-mentioned mixed material is achieved by adjusting the material mixing ratio.

[0008] If the graded optical band gap high refractive index material layer H i The layer adopts nano-laminated material, and its structure is B , where the sublayer Thickness and sublayers Thickness Satisfies the following formula: Where, For material H CH The refractive index, For material H CL The refractive index, N is the total number of gradient optical band gap high refractive index material layers, B is the number of sublayer periods, and B >0, λ is the reference wavelength.

[0009] If the graded optical band gap high refractive index material layer H i The layer adopts mixed materials, whose component materials H CL and H CH Mixing ratio Satisfies the following formula: Where, For material H CH The refractive index, For material H CL The refractive index, H i The refractive index of the layer.

[0010] The above-mentioned gradient optical band gap high refractive index material layer H i Refractive index of the layer Satisfies the following formula: The above-mentioned low refractive index material layer L is SiO2 material; the above-mentioned fixed optical band gap high refractive index material layer Y is composed of nano-laminated material or mixed material H CL Material.

[0011] The above-mentioned nano-laminated material is Al2O3 / HfO2 laminated material, Al2O3 / Ta2O5 laminated material or SiO2 / HfO2 laminated material, etc.

[0012] The above-mentioned mixed material is Al2O3-HfO2 mixed material, Al2O3-Ta2O5 mixed material or SiO2-HfO2 mixed material, etc.

[0013] A method for preparing a high damage threshold laser reflective film based on a graded optical band gap high refractive index material is characterized in that the method comprises the following steps: S1. Parameter input: including reference wavelength λ , the refractive index of the substrate , two materials H that make up the nano-laminated material or mixed material CH and H CL Refractive index and , the refractive index of the low refractive index material layer L ,in, Gradient optical band gap high refractive index material layer H i Total number of layers N , the refractive index of the fixed optical band gap high refractive index material layer Y , and the number of cycles m ; S2. Membrane system design: 1) Calculate the H of each graded optical band gap high refractive index material layer i Refractive index of the layer ; 2) When the graded optical band gap high refractive index material layer uses nano-laminated materials, calculate H i Neutron layer Thickness and sublayers Thickness ; Set the sublayer period number B; When the graded optical band gap high refractive index material layer uses a mixed material, calculate H i Component material H in the layer CL With component material H CH Mixing ratio ; and calculated according to the conventional optical film design method to obtain H i The film thickness of the layer; 3) Calculate the thickness of the remaining layers in the film structure according to conventional optical thin film design methods; 4) Setting coefficients k and j ; 5) Output film structure: substrate| k LH1LH2L……H N L(YL) m j L|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°C~230°C; when the vacuum degree is better than 9.0×10 -3 When Pa, multiple layers of films are deposited on the substrate according to the film system design structure until the last thin film layer.

[0014] The multilayer film is prepared by deposition methods such as electron beam co-evaporation, ion beam co-sputtering or atomic layer deposition.

[0015] Mixing ratio of the above mixed materials By adjusting the component material H CL With component material H CH The deposition rate was obtained.

[0016] Technical effects of the present invention: 1. The present invention utilizes a nano-laminated material or hybrid material with a gradually increasing optical band gap as a high-refractive-index material layer from the substrate to the film surface, replacing the high-refractive-index material layer with a fixed optical band gap in conventional laser reflective films. The peak electric field intensity in the dielectric reflective film with a regular film structure gradually increases from the substrate toward the film surface. On the one hand, the use of materials with larger optical band gaps in areas of higher electric field intensity can improve the laser damage threshold of the laser reflective film. On the other hand, materials with smaller optical band gaps tend to have a larger refractive index. Using high-refractive-index materials with relatively smaller optical band gaps in areas of lower electric field intensity can increase the reflectivity and reflection bandwidth of the laser reflective film.

[0017] 2. The high-refractive-index material layer with a gradually increasing optical bandgap of the present invention can be made of either nano-laminated materials or hybrid materials. Coating equipment that cannot deposit two materials simultaneously can also achieve the effects of the present invention using nano-laminated materials, thereby improving the applicability of thin-film fabrication equipment. Furthermore, the optical bandgap of nano-laminated materials is achieved by adjusting the thickness ratio of the sub-layer materials, while the optical bandgap of hybrid materials is achieved by adjusting the mixing ratio of the materials, increasing flexibility in thin-film design and fabrication.

[0018] 3. The present invention can significantly improve the damage threshold of the laser reflective film without significantly affecting the optical and mechanical properties of the laser reflective film.

[0019] 4. The present invention is very suitable for the preparation of short-pulse intense laser thin film components. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic diagram of the film structure of the high damage threshold laser reflective film based on the gradient optical band gap high refractive index material of the present invention.

[0021] Figure 2 This is a probability distribution diagram of laser damage of the laser reflective film made of a gradient optical band gap and a high refractive index material prepared in Example 1 of the present invention and the laser reflective film made of a traditional fixed optical band gap and a high refractive index material prepared in a comparative example. DETAILED DESCRIPTION

[0022] The present invention will be further described below with reference to the embodiments and drawings, but this should not limit the scope of protection of the present invention. Figure 1 , Figure 1This is a schematic diagram of the film structure of the high damage threshold laser reflective film based on the gradient optical band gap high refractive index material of the present invention.

[0023] Example 1 Using Al2O3 / HfO2 stacked materials as the high-refractive-index material and SiO2 as the low-refractive-index material, a laser-reflective film with a reflectivity exceeding 99.5% at 1053nm was designed and fabricated. By varying the thickness ratio of the Al2O3 and HfO2 sublayers in the Al2O3 / HfO2 stacked materials, the optical bandgap of the high-refractive-index material layer was tuned. The steps are as follows: ① Input parameters: reference wavelength of 1207 nm, substrate refractive index of 1.52, refractive indices of the HfO2 sublayer and Al2O3 sublayer of the Al2O3 / HfO2 nanolaminate of 1.891 and 1.602, respectively, refractive index of the SiO2 low-refractive-index material layer of 1.452, sublayer period number of 4, number of high-refractive-index material layers with a gradient optical band gap of 11, number of Al2O3 layers with a fixed optical band gap of 5 (i.e., period number m = 5), and refractive index of the Al2O3 layer of 1.602; ② According to formula (1), calculate the i layer( i =1, 2, 3...11) High refractive index material layer H with gradient optical band gap i Refractive index of the layer : (1) ③Gradual optical band gap high refractive index material layer H i layer( i =1,2,3……11) is a structure of [ 4 Nano-laminated materials, sub-layer The material of the sublayer is HfO2, with a refractive index of 1.891. The material of the layer is Al2O3, with a refractive index of 1.602. The sublayer is calculated according to formula (2) Thickness of HfO2 layer , calculate the sub-layer according to formula (3) Thickness of Al2O3 layer : (2) (3) Calculate H i The thickness of the sub-layer materials in the layer is shown in the following table.

[0024] Table 1 Graded optical band gap high refractive index material layer H in Example 1 i Thickness of the sublayer material in the layer ④Computer output film structure: Substrate|2LH1LH2L……H 10 LH 11 L(YL) 5 3.15L|air; the thicknesses of the Y layer and L layer are 188.4nm and 207.8nm, respectively.

[0025] ⑤Substrate cleaning and clamping: After cleaning and drying the substrate, clamp it into the fixture of the coating equipment; ⑥ Thin film preparation: Heat the substrate to 200℃; when the vacuum degree is better than 9.0×10 -4 When Pa, electron beam evaporation deposition technology is used to deposit multiple layers of film on the substrate according to the film structure design until the last layer of film. N The above structure is deposited alternately in layers 4 Al2O3 / HfO2 nano-laminated materials.

[0026] Comparative Example Using electron beam evaporation deposition technology, the film structure is prepared as substrate|2L(ML) 16 A traditional fixed optical band gap high refractive index material laser reflective film with a thickness of 3.15L|air, wherein the high refractive index material layer M is an Al2O3-HfO2 mixed material with a fixed mixing ratio of 0.69:0.31, and the low refractive index material layer L is SiO2 material.

[0027] Laser damage threshold measurement: According to the ISO 21254 test standard, damage threshold tests were conducted on the laser reflective films prepared in Example 1 and the comparative example using a 1-on-1 test method. Laser wavelength: 1053 nm, pulse width: 8 ps, incident angles: 56° (Example 1 sample) and 50.1° (Comparative Example sample), polarization state: s component. The test results show that the laser reflective films prepared by the present method have a high laser damage threshold, reaching ~9.4 J / cm at a wavelength of 1053 nm. 2 , which is higher than the traditional fixed optical band gap high refractive index material laser reflective film (~6.3J / cm 2 ). Figure 2 Shown are the laser damage probability distribution diagrams of the laser reflective film made of a gradient optical band gap high refractive index material prepared in Example 1 of the present invention and the laser reflective film made of a traditional fixed optical band gap high refractive index material prepared in the comparative example.

[0028] Example 2 Using an Al2O3-HfO2 hybrid material as the high-refractive-index material and SiO2 as the low-refractive-index material, a laser-reflective film with a reflectivity exceeding 99.5% at 1053nm was designed and fabricated. By varying the ratio of Al2O3 to HfO2 in the Al2O3-HfO2 hybrid, the optical bandgap of the high-refractive-index layer was tuned.

[0029] In addition to Al2O3 / HfO2 stacks and Al2O3-HfO2 hybrids, high-damage-threshold laser reflective films can also be designed and fabricated using Al2O3 / Ta2O5 stacks, SiO2 / HfO2 stacks, Al2O3-Ta2O5 hybrids, or SiO2-HfO2 hybrids as the high-refractive-index material, and SiO2 as the low-refractive-index material. By varying the thickness ratio of the sublayers in the nano-stacked material or the material mix ratio in the hybrid, the optical bandgap of the high-refractive-index material layer can be tuned.

Claims

1. A high damage threshold laser reflective film based on a graded optical band gap high refractive index material, characterized in that: The membrane structure is substrate| k LH1LH2L……H N L(YL) m j L|air; substrate is the base; air is air; L is a low refractive index material layer; H i It is a gradient optical band gap high refractive index material layer, and its optical band gap gradually increases from the substrate to the film surface. i=1,2,3……N ; Y is a layer of high refractive index material with a fixed optical band gap; m is the number of cycles, and m ≥0; k and j is the coefficient, and 0≤ k≤ 8, j The value of makes the electric field at the interface between air and film layer equal to 0.

2. The high damage threshold laser reflective film based on a graded optical band gap high refractive index material according to claim 1, characterized in that: The gradient optical band gap high refractive index material layer is a nano-laminated material or a mixed material. CH and material H CL composition.

3. The high damage threshold laser reflective film based on a graded optical band gap high refractive index material according to claim 2, characterized in that: The optical band gap of the nano-laminated material is achieved by adjusting the thickness ratio of the sub-layer materials, and the optical band gap of the mixed material is achieved by adjusting the material mixing ratio.

4. The high damage threshold laser reflective film based on a graded optical band gap high refractive index material according to claim 2 or 3, characterized in that: If the graded optical band gap high refractive index material layer H i The layer adopts nano-laminated material, and its structure is B , where the sublayer Thickness and sublayers Thickness Satisfies the following formula: Where, For material H CH The refractive index, For material H CL The refractive index, N is the total number of gradient optical band gap high refractive index material layers, B is the number of sublayer periods, and B >0, λ is the reference wavelength.

5. The high damage threshold laser reflective film based on a graded optical band gap high refractive index material according to claim 2 or 3, characterized in that: If the graded optical band gap high refractive index material layer H i The layer adopts mixed materials, whose component materials H CL and H CH Mixing ratio Satisfies the following formula: Where, For material H CH The refractive index, For material H CL The refractive index, H i The refractive index of the layer.

6. The high damage threshold laser reflective film based on a graded optical band gap high refractive index material according to any one of claims 1 to 3, characterized in that: The gradient optical band gap high refractive index material layer H i Refractive index of the layer Satisfies the following formula: 。 7. The high damage threshold laser reflective film based on a graded optical band gap high refractive index material according to claim 1, characterized in that: The low refractive index material layer L is SiO2 material; the fixed optical band gap high refractive index material layer Y is composed of nano-laminated material or mixed material H CL Material.

8. The high damage threshold laser reflective film based on a graded optical band gap high refractive index material according to claim 2 or 3, characterized in that: The nano-laminated material is an Al2O3 / HfO2 laminated material, an Al2O3 / Ta2O5 laminated material or a SiO2 / HfO2 laminated material.

9. The high damage threshold laser reflective film based on a graded optical band gap high refractive index material according to claim 2 or 3, characterized in that: The mixed material is an Al2O3-HfO2 mixed material, an Al2O3-Ta2O5 mixed material or a SiO2-HfO2 mixed material.

10. A method for preparing a high damage threshold laser reflective film based on a graded optical band gap high refractive index material according to any one of claims 1 to 9, characterized in that: The method comprises the following steps: S1. Parameter input: including reference wavelength λ , the refractive index of the substrate , two materials H that make up the nano-laminated material or mixed material CH and H CL Refractive index and , the refractive index of the low refractive index material layer L ,in, Gradient optical band gap high refractive index material layer H i Total number of layers N , the refractive index of the fixed optical band gap high refractive index material layer Y , and the number of cycles m ; S2. Membrane system design: 1) Calculate the H of each graded optical band gap high refractive index material layer i Refractive index of the layer ; 2) When the graded optical band gap high refractive index material layer uses nano-laminated materials, calculate H i Neutron layer Thickness and sublayers Thickness ; Set the sublayer period number B; When the graded optical band gap high refractive index material layer uses a mixed material, calculate H i Component material H in the layer CL With component material H CH Mixing ratio ; and calculated according to the conventional optical film design method to obtain H i The film thickness of the layer; 3) Calculate the thickness of the remaining layers in the film structure according to conventional optical thin film design methods; 4) Setting coefficients k and j ; 5) Output film structure: substrate| k LH1LH2L……H N L(YL) m j L|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°C~230°C; when the vacuum degree is better than 9.0×10 -3 When Pa, multiple layers of films are deposited on the substrate according to the film system design structure until the last thin film layer.

11. The method for preparing a high damage threshold laser reflective film based on a graded optical band gap high refractive index material according to claim 10, characterized in that: The multilayer film is prepared by a deposition method of electron beam co-evaporation, ion beam co-sputtering or atomic layer deposition.

12. The method for preparing a high damage threshold laser reflective film based on a graded optical band gap high refractive index material according to claim 10, 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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