Nanometer composite ultralow-absorption low-loss film

Abstract

The invention belongs to the technical field of optical thin films, and discloses a nano composite ultralow-absorption low-loss thin film which sequentially comprises a substrate, a composite high-reflection film layer and an absorption loss regulation and control layer from bottom to top, the composite high-reflection film layer is formed by alternately plating element-doped nano composite low-absorption high-refractive-index materials and low-refractive-index materials in a specific asymmetric thickness, the absorption and loss of the composite high-refractive-index materials are reduced in an element-doped nano composite mode, the thickness ratio of the high-refractive-index materials to the low-refractive-index materials is regulated, the absorption of the film is reduced, and the film has a good reflection effect. The absorption loss regulation and control layer reduces the overall absorption and loss of the thin film by regulating and controlling a central wavelength electric field. According to the invention, the nano composite low-absorption high-refractive-index material, the composite high-reflection film layer with the thickness of the high-refractive-index material and the thickness of the low-refractive-index material in a certain proportion, and the absorption loss regulation and control layer structure are utilized, so that the absorption and loss of the film can be greatly reduced, and the sub-ppm-level ultralow-absorption low-loss film is realized; and a key element is provided for a high-power laser system and an ultra-high precision measurement system.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical films, and in particular relates to a nano-composite ultra-low absorption and low loss film. Background Art

[0002] Ultra-low absorption, low-loss films are core optical components in high-power laser systems and ultra-high-precision measurement systems. Their absorption loss is a significant factor limiting the output power of high-power laser systems and the sensitivity and signal-to-noise ratio of precision measurement systems. Traditional ultra-low absorption, low-loss films are composed of multiple layers of high- and low-refractive-index materials, leveraging optical interference to achieve ultra-high reflectivity. Furthermore, film absorption and loss performance are enhanced through processes such as reducing film defects, increasing film density, and performing post-processing.

[0003] Zhang Jinlong et al. [CN107748404B] proposed a highly reflective film with low scattering losses. The film consists of a substrate, a first film, a second film, and a third film. The first film is a standard highly reflective film structure with an optical thickness of 1 / 4 the central wavelength, while the second and third films are all-dielectric Fabry-Perot cavity films. While the introduction of the Fabry-Perot cavity structure reduces scattering losses, it does not fundamentally address the issues of material absorption and total loss. The film losses are still in the order of several ppm to tens of ppm, making it difficult to meet the ultra-low absorption loss requirements of sub-ppm levels for high-power lasers and ultra-high-precision measurement systems.

[0004] Therefore, there is an urgent need for a new film structure and its preparation method that can synergistically reduce absorption and loss at the material level and structural level, and realize a truly ultra-low absorption and low-loss optical film. Summary of the Invention

[0005] The present invention aims to solve the technical problem that the existing high-reflection film has high absorption loss and is difficult to achieve ultra-low loss at the sub-ppm level. It provides a nano-composite ultra-low absorption and low-loss film. It utilizes a nano-composite low-absorption high-refractive index material, a composite high-reflective film layer with a certain ratio of high and low refractive index material thicknesses, and an absorption loss regulation layer structure to greatly reduce the absorption and loss of thin film components, achieve ultra-low absorption and low loss film at the sub-ppm level, and provide a key component for high-power laser systems and ultra-high precision measurement systems.

[0006] The technical solutions of the present invention are as follows: A nanocomposite ultra-low absorption and low-loss film characterized by a film structure expressed as: S / (aMbL)^ncMdL / A, where S represents the substrate, (aMbL)^n represents the composite high-reflective film layer, and is composed of element-doped nanocomposite low-absorption high-refractive index film layers M and low-refractive index film layers L, alternately deposited at specific thickness ratios. M represents a composite high-refractive index film layer with an optical thickness of 1 / 4 wavelength, L represents a low-refractive index film layer with an optical thickness of 1 / 4 wavelength, n represents the number of composite high-reflective film layers, and a and b represent the optical thickness coefficients of the composite high-refractive index material and the low-refractive index material in the composite high-reflective film layer, respectively. In the composite high-reflective film layer, a / b < 1, and a + b = 2 are satisfied. The composite high-refractive index film layer M is a mixture of two or more pure high-refractive index materials, achieving lower absorption loss than a pure single high-refractive index material. cMdL represents the absorption loss control layer, and c and d represent the optical thickness control coefficients of the composite high-refractive index material and the low-refractive index material in the absorption loss control layer, respectively. The absorption loss control layer reduces the electric field intensity and embedding depth at the center wavelength by adjusting the c and d coefficients, thereby reducing the overall absorption and loss of the film. A represents the incident medium.

[0007] The composite high refractive index material M can be doped with two or three materials including TiO2, Ta2O5, Nb2O5, HfO2, Al2O3, ZnO, Y2O3, ZrO2, Sc2O3 and GeO2; the low refractive index material is SiO2, YbF3 or MgF2.

[0008] The composite high-refractive index material M can be prepared by ion beam co-sputtering, magnetron co-sputtering, atomic layer co-deposition or electron beam dual-source co-evaporation.

[0009] The substrate is quartz, sapphire, CaF2, Ge, Si or ZnSe.

[0010] Ultra-low absorption and low loss thin film components can be achieved by regulating the proportion of composite low-absorption and high-refractive index materials, composite high-reflection film layers, and absorption loss control layer coefficients.

[0011] Compared with the prior art, the technical effects of the present invention are as follows: 1. The nano-composite ultra-low absorption and low-loss film provided by the present invention effectively solves the absorption limitations of traditional high-refractive index film layers and the overall absorption loss problems of thin film components, greatly improves the absorption and loss performance of optical thin film components, and can achieve sub-ppm ultra-low absorption and low-loss films, thereby improving the output power of high-power laser systems and the test accuracy of ultra-high precision measurement systems.

[0012] 2. The membrane system of the present invention has a simple structure, multiple material choices, and multiple preparation technologies, and has broad application prospects in the fields of high-power laser and ultra-high precision measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a schematic diagram of the structure of nano-composite ultra-low absorption and low loss film.

[0014] Figure 2 This is a structural diagram of a nano-composite ultra-low absorption and low loss thin film system with a central wavelength of 1064nm.

[0015] Figure 3 This is the electric field distribution diagram of the nano-composite ultra-low absorption and low loss film with a central wavelength of 1064nm.

[0016] Figure 4 This is a structural diagram of a nano-composite ultra-low absorption and low loss thin film system with a central wavelength of 633nm.

[0017] Figure 5 This is the electric field distribution diagram of the nano-composite ultra-low absorption and low loss film at 1064nm with a central wavelength of 633nm. DETAILED DESCRIPTION

[0018] The present invention will be further described below with reference to examples and drawings, but the scope of protection of the present invention should not be limited thereto.

[0019] See also Figure 1 , Figure 1 This is a schematic diagram of the structure of a nanocomposite ultra-low absorption, low-loss film. The film structure is represented by: S / (aMbL)^ncMdL / A, where S represents the substrate, (aMbL)^n represents the composite high-reflective film layer, which is composed of element-doped nanocomposite low-absorption high-refractive index material M and low-refractive index material L alternately deposited at a specific thickness ratio, M represents a composite high-refractive index film layer with an optical thickness of 1 / 4 wavelength, L represents a low-refractive index film layer with an optical thickness of 1 / 4 wavelength, n represents the number of composite high-reflective film layers, and a and b represent the optical thickness coefficients of the composite high-refractive index material and low-refractive index material in the composite high-reflective film layer, respectively. In the composite high-reflective film layer, a / b < 1, and a + b = 2, the composite high-refractive index material M is a mixture of two or more pure high-refractive index materials, achieving lower absorption loss than a pure single high-refractive index material. cMdL represents the absorption loss control layer, and c and d represent the optical thickness control coefficients of the composite high-refractive index material and low-refractive index material in the absorption loss control layer, respectively. The absorption loss control layer reduces the electric field intensity and embedding depth at the center wavelength by adjusting the c and d coefficients, thereby reducing the overall absorption and loss of the film. A represents the incident medium.

[0020] Example 1: Nanocomposite ultra-low absorption and low loss film for a central wavelength of 1064 nm Thin film structure design: The nanocomposite ultra-low absorption and low loss film is: quartz substrate / (0.9M1.1L)^20 / 0.95M4.01L / air. S (substrate): Made of standard optical grade fused silica (JGS1).

[0021] M (composite high refractive index material): TiO2 and Ta2O5 are nanocomposited using ion beam co-sputtering technology. The molar ratio of the two materials is 1:99. This ratio, calculated from molecular dynamics simulations, aims to leverage the low absorption properties of Ta2O5 and the high refractive index of TiO2. While achieving a high refractive index, the doping of TiO2 inhibits crystallization, reduces defects and absorption centers, and ultimately results in a composite material with an absorption coefficient lower than that of pure Ta2O5 and pure TiO2.

[0022] L (low refractive index material): Select SiO2.

[0023] (aMbL)^n (composite high-reflection film): period number n = 20. The optical thickness of the M layer is 0.9 × (λ / 4), and the optical thickness of the L layer is 1.1 × (λ / 4). This asymmetric design of a / b = 0.9 / 1.1 < 1 is intended to push more optical electric field energy from the relatively high-absorbing M layer to the extremely low-absorbing L layer (SiO2), thereby structurally reducing absorption losses throughout the stack.

[0024] cMdL (absorption loss control layer): By optimizing the coefficients (c=0.95, d=4.01), this two-layer structure, as a whole, "pushes" the optical electric field peak at 1064nm away from the film-air interface and distributes it primarily within the outermost, thick, low-refractive-index SiO2 layer (4.01×λ / 4). Because SiO2 has extremely low absorption losses and the electric field intensity is significantly suppressed in the high-refractive-index M layer (0.95×λ / 4), the overall absorption loss of the entire film is greatly reduced.

[0025] The structure of nanocomposite ultra-low absorption loss film can be written as: S / (0.9M1.1L)^20 0.95M4.01L / A, and the film thickness is as follows: Figure 2 As shown, the electric field distribution at 1064nm is as follows Figure 3 By adjusting the optical thickness ratio of the composite high-refractive index material and the composite high-reflective film layer, as well as the thickness coefficient of the absorption loss layer, the absorption loss at 1064nm can be reduced to less than 0.5ppm.

[0026] Example 2: For the nano-composite ultra-low absorption and low loss film with a central wavelength of 633nm, the substrate S is quartz, and the composite high refractive index material M is HfO2 and Ta2O5 doped in a ratio of 5:95. Based on molecular dynamics simulation, the optimal doping ratio of the composite low-absorption and low-damage film is calculated. The absorption of the composite film material is lower than that of pure HfO2 and Ta2O5 materials through element doping. SiO2 is selected as the low refractive index material L. The optical thickness coefficients of the composite high refractive index material and the low refractive index material are 0.95 and 1.05, respectively. The period number n of the composite high-refractive index film is 25. Since the absorption of the film interface and the high refractive index material is greater than that of the low refractive index material, by adjusting the optical thickness coefficients of the outermost two layers of the film, the electric field peak at 633nm is moved to the low refractive index material, and the peak electric field intensity in the composite high refractive index material and the low refractive index is reduced, the overall absorption loss of the film can be further reduced. Finally, the absorption loss of the absorption loss layer is adjusted to 0.986 and 4.005, respectively. The structure of nanocomposite ultra-low absorption loss film can be written as: S / (0.95M1.05L)^250.986M4.005L / A, where A is air and the film thickness is as follows: Figure 4 As shown, the electric field distribution at 633nm is as follows Figure 5 By adjusting the optical thickness ratio of the composite high-refractive index material and the composite high-reflective film layer, as well as the thickness coefficient of the absorption loss layer, the absorption loss at 633nm can be reduced to less than 1ppm.

Claims

1. A nanocomposite ultra-low absorption and low loss film, characterized in that: The film is stacked from bottom to top with a substrate, a composite high-reflection film layer, an absorption loss control layer, and an incident medium layer; its structure is expressed as: S / (aMbL)^ncMdL / A, where: S stands for substrate; (aMbL)^n represents a composite high-reflective film layer, which is stacked by n periods. Each period includes a composite high-refractive index film layer M with an optical thickness of a / 4λ and a low-refractive index film layer L with an optical thickness of b / 4λ, where λ is the designed central wavelength, a / b<1, and a+b=2. The composite high-refractive index film layer M is composed of two or three high-refractive index materials through element-doped nanocomposites, and its absorption loss is lower than that of any single component pure material; cMdL represents an absorption loss control layer, comprising a composite high-refractive index film layer M with an optical thickness of c / 4λ and a low-refractive index film layer L with an optical thickness of d / 4λ, where c and d represent the optical thickness control coefficients of the composite high-refractive index material and the low-refractive index material in the absorption loss control layer, respectively, and are used to control the electric field intensity and distribution at the central wavelength; A represents an incident dielectric layer, which is in contact with the outermost surface of the absorption loss control layer.

2. The nanocomposite ultra-low absorption and low loss film according to claim 1, characterized in that: The composite high refractive index film layer M is selected from a mixture of two or three of TiO2, Ta2O5, Nb2O5, HfO2, Al2O3, ZnO, Y2O3, ZrO2, Sc2O3 and GeO2; the low refractive index film layer L is SiO2, YbF3 or MgF2.

3. The nanocomposite ultra-low absorption and low loss film according to claim 1, wherein: The composite high refractive index film layer M is prepared by ion beam co-sputtering, magnetron co-sputtering, atomic layer co-deposition or electron beam dual-source co-evaporation to achieve uniform composite at the nanometer scale.

4. The nanocomposite ultra-low absorption and low loss film according to claim 1, wherein: The substrate is quartz, sapphire, CaF2, Ge, Si or ZnSe.

5. The nanocomposite ultra-low absorption and low loss film according to any one of claims 1 to 4, characterized in that: The absorption loss control layer reduces the electric field intensity at the center wavelength and the embedding depth of the electric field in the film layer by optimizing the coefficients c and d, thereby reducing the overall absorption loss of the film at the target center wavelength to the sub-ppm level.

6. The nanocomposite ultra-low absorption and low loss film according to any one of claims 1 to 4, characterized in that: The period number n of the composite high-reflection film layer ranges from 10 to 30.

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