A nanocomposite ultra-low-absorption low-loss film

Abstract

The application belongs to the technical field of optical film, and discloses a kind of nanocomposite ultra-low absorption low-loss film, from bottom to top, including substrate, composite high reflection film layer and absorption loss control layer in turn, wherein, composite high reflection film layer is alternately plated by element doped nanocomposite low absorption high refractive index material and low refractive index material with specific asymmetric thickness, composite high refractive index material reduces its absorption and loss by element doped nanocomposite way, and the thickness ratio of high and low refractive index material is regulated, to reduce the absorption of film, absorption loss control layer is by regulating central wavelength electric field to reduce the overall absorption and loss of film.The application utilizes nanocomposite low absorption high refractive index material, composite high reflection film layer with high and low refractive index material thickness in a certain proportion and absorption loss control layer structure, which can greatly reduce the absorption and loss of film, realize sub-ppm level ultra-low absorption low-loss film, and provide key components for high-power laser system and super-high precision measurement system.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of optical films, and particularly relates to a nanocomposite ultra-low absorption and low loss film. BACKGROUND

[0002] The ultra-low absorption and low loss film is a core optical element in a high-power laser system and an ultra-high precision measurement system, and its absorption loss is an important factor for limiting the output power of the high-power laser system and the sensitivity and signal-to-noise ratio of the precision measurement system. The traditional ultra-low absorption and low loss film is stacked by multiple layers of high and low refractive index materials, and realizes ultra-high reflection by using optical interference effect. On this basis, the film absorption and loss performance is improved by reducing film layer defects, improving compactness and post-processing and the like.

[0003] Zhang Jinlong et al.

CN107748404B

[0004] Therefore, there is an urgent need for a new film structure and a preparation method thereof, which can synergistically reduce absorption and loss at the material and structural levels to realize a truly ultra-low absorption and low loss optical film. SUMMARY

[0005] The application aims to solve the technical problems of high absorption and loss of the existing high reflection film and difficulty in realizing sub-ppm level ultra-low loss, and provides a nanocomposite ultra-low absorption and low loss film. The film layer is composed of nanocomposite low absorption and high refractive index material, high and low refractive index material with a certain proportion of thickness, and an absorption and loss regulation layer structure, which can greatly reduce the absorption and loss of the film element, realize sub-ppm level ultra-low absorption and low loss film, and provide key elements for high-power laser systems and ultra-high precision measurement systems.

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

[0007] The application discloses a kind of nanocomposite ultra-low absorption low-loss film, its film structure is expressed as: S / (aMbL)^ ncMdL / A, wherein S represents substrate, (aMbL)^ n represents composite high-reflection film layer, is alternately plated by the thickness of element-doped nanocomposite low-absorption high-refractive index film layer M and low-refractive index film layer L in specific proportion, M represents composite high-refractive index film layer with optical thickness of 1 / 4 wavelength, L represents low-refractive index film layer with optical thickness of 1 / 4 wavelength, n represents the number of composite high-reflection film layer period, a and b respectively represent the optical thickness coefficient of composite high-refractive index material and low-refractive index material in composite high-reflection film layer.The a / b of the composite high-reflection film layer described in the specification is less than 1, and satisfies a+b=2, the composite high-refractive index film layer M is mixed by two or more pure high-refractive index materials, to realize that the absorption loss is lower than pure single high-refractive index material.CMdL represents absorption loss control layer, and c and d respectively represent the optical thickness control coefficient of composite high-refractive index material and low-refractive index material in absorption loss control layer.The absorption loss control layer reduces the electric field intensity and embedding depth at the center wavelength by adjusting the coefficients c and d, thereby reducing the overall absorption and loss of the film.A represents incident medium.

[0008] The composite high-refractive index material M can be TiO2, Ta2O5, Nb2O5, HfO2, Al2O3, ZnO, Y2O3, ZrO2, Sc2O3 and GeO2 doped with two or three materials, and the low-refractive index material is SiO2, YbF3 or MgF2.

[0009] 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 double-source co-evaporation.

[0010] The substrate is quartz, sapphire, CaF2, Ge, Si or ZnSe.

[0011] By controlling the proportion of composite low-absorption high-refractive index material, composite high-reflection film layer and absorption loss control layer coefficient, an ultra-low absorption low-loss film element is realized.

[0012] Compared with the prior art, the technical effects of the application are as follows:

[0013] 1、The nanocomposite ultra-low absorption low-loss film provided by the application effectively solves the problems of absorption limitation of traditional high-refractive index film layer and overall absorption and loss of film element, greatly improves the absorption and loss performance of optical film element, can realize sub-ppm level ultra-low absorption low-loss film, and further improves the output power of high-power laser system and the test precision of ultra-high precision measurement system.

[0014] 2、The film has simple structure, multiple material selection and multiple preparation technology, and has wide application prospect in the fields of high-power laser and ultra-high precision measurement. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 is a schematic diagram of a nano-composite ultra-low absorption and low loss thin film structure.

[0016] Figure 2 is a nano-composite ultra-low absorption and low loss thin film structure diagram with a center wavelength of 1064 nm.

[0017] Figure 3 is a 1064 nm electric field distribution diagram of a nano-composite ultra-low absorption and low loss thin film with a center wavelength of 1064 nm.

[0018] Figure 4 is a nano-composite ultra-low absorption and low loss thin film structure diagram with a center wavelength of 633 nm.

[0019] Figure 5 is a 1064 nm electric field distribution diagram of a nano-composite ultra-low absorption and low loss thin film with a center wavelength of 633 nm. DETAILED DESCRIPTION

[0020] The application will be further described below through examples and drawings, but the protection scope of the application should not be limited thereby.

[0021] Please refer to Figure 1 , Figure 1 is a schematic diagram of a nano-composite ultra-low absorption and low loss thin film structure, and the thin film structure is represented as: S / (aMbL)^ncMdL / A, wherein S represents a substrate, (aMbL)^n represents a composite high-reflection film layer, which is formed by alternately plating a nano-composite low-absorption high-refractive material M and a low-refractive material L with a specific ratio of thickness, M represents a composite high-refractive film layer with an optical thickness of 1 / 4 wavelength, L represents a low-refractive film layer with an optical thickness of 1 / 4 wavelength, n represents the number of periods of the composite high-reflection film layer, and a and b respectively represent the optical thickness coefficients of the composite high-refractive material and the low-refractive material in the composite high-reflection film layer. The composite high-reflection film layer has a / b<1 and satisfies a+b=2, the composite high-refractive material M is mixed by two or more pure high-refractive materials to realize lower absorption and loss than pure single high-refractive material. cMdL represents an absorption and loss regulating layer, and c and d respectively represent the optical thickness regulating coefficients of the composite high-refractive material and the low-refractive material in the absorption and loss regulating layer. The absorption and loss regulating layer reduces the electric field intensity and embedding depth at the center wavelength by adjusting the coefficients c and d, thereby reducing the overall absorption and loss of the thin film. A represents an incident medium.

[0022] Example 1: Nanocomposite ultra-low absorption low-loss film for central wavelength 1064 nm

[0023] Film structure design:

[0024] The nanocomposite ultra-low absorption low-loss film is: quartz substrate / (0.9M1.1L)^20 / 0.95M4.01L / air. Among them:

[0025] S (substrate): Standard optical grade fused quartz (JGS1) is used.

[0026] M (composite high refractive index material): TiO2 and Ta2O5 are selected, and nanocomposite is carried out by ion beam co-sputtering technology. The doping molar ratio of the two materials is 1:99. This ratio is the best value calculated by molecular dynamics simulation, aiming to utilize the low absorption characteristics of Ta2O5 and the high refractive index characteristics of TiO2, to obtain high refractive index while suppressing the crystallization of Ta2O5, reducing defects and absorption centers through TiO2 doping, and finally making the absorption coefficient of the composite material lower than that of pure Ta2O5 and pure TiO2.

[0027] L (low refractive index material): SiO2 is selected.

[0028] (aMbL)^n (composite high reflection film layer): The number of periods n=20. The optical thickness of M layer is 0.9×(λ / 4), and the optical thickness of L layer is 1.1×(λ / 4). This a / b=0.9 / 1.1<1 asymmetric design aims to push more optical electric field energy from the M layer with relatively high absorption to the L layer (SiO2) with extremely low absorption, thereby preliminarily reducing the absorption loss of the entire stack from the structure.

[0029] cMdL (absorption loss regulation layer): By optimizing the coefficient (c=0.95, d=4.01), this two-layer structure as a whole "pushes" the optical electric field peak at 1064 nm away from the film-air interface and mainly distributes it in the outermost thick low refractive index SiO2 layer (4.01×λ / 4). Since SiO2 has extremely low absorption loss, and the intensity of the electric field in the high refractive index M layer (0.95×λ / 4) is significantly suppressed, the overall absorption loss of the entire film is greatly reduced.

[0030] The nanocomposite ultra-low absorption loss film structure can be written as: S / (0.9M1.1L)^20 0.95M4.01L / A, the film layer thickness is as shown in Figure 2 , and the electric field distribution at 1064 nm is as shown in Figure 3 . By adjusting the optical thickness ratio of the composite high refractive index material, the composite high reflection film layer, and the thickness coefficient of the absorption loss layer, the 1064 nm absorption loss can finally be less than 0.5 ppm.

[0031] Example 2:

[0032] For the nanocomposite ultra-low absorption and low loss film with a center wavelength of 633 nm, the substrate S is quartz, the composite high refractive index material M is HfO2 and Ta2O5 doped in a ratio of 5:95, and the optimal doping ratio of the composite low absorption and low damage film is calculated based on molecular dynamics simulation. The composite thin film material is doped with elements to make the absorption lower than that of pure HfO2 and Ta2O5 materials. The low refractive index material L is SiO2. 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 number of composite high reflection film layers n is 25. Since the film layer interface and the high refractive index material have higher absorption than the low refractive index material, under the condition of ensuring the overall spectrum of the film and the reflectivity at 633 nm, by adjusting the optical thickness coefficients of the outermost two layers of the film, the peak value of the electric field at 633 nm is moved to the low refractive index material, and the intensity of the peak electric field in the composite high refractive index material and the low refractive index material is reduced, which can further reduce the overall absorption loss of the film. The final absorption loss of the absorption loss layer is 0.986 and 4.005, respectively. The structure of the nanocomposite ultra-low absorption and low loss film can be written as: S / (0.95M1.05L)^250.986M4.005L / A, A is air, the thickness of the film layers is shown in Figure 4 , and the electric field distribution at 633 nm is shown in Figure 5 . By adjusting the optical thickness ratio of the composite high refractive index material, the composite high reflection film layer, and the thickness coefficient of the absorption loss layer, the absorption loss at 633 nm can be less than 1 ppm.

Claims

1. A nanocomposite ultra-low absorbing low-loss thin film, characterized in that, The thin film is sequentially stacked from bottom to top with a substrate, a composite high-reflection film layer, an absorption-loss regulating layer and an incident medium layer; the structure is represented as: S / (aMbL)^ncMdL / A, wherein: S represents the substrate; (aMbL)^n represents the composite high-reflection film layer, stacked by n periods, each period comprising a composite high-refraction film layer M with an optical thickness of a / 4λ and a low-refraction film layer L with an optical thickness of b / 4λ, wherein λ is the design center wavelength, and a / b < 1, a+b = 2, the composite high-refraction film layer M is composed of two or three high-refraction materials by element doping nanocomposite, and the absorption loss is lower than that of any single component pure material; cMdL represents the absorption-loss regulating layer, comprising a composite high-refraction film layer M with an optical thickness of c / 4λ and a low-refraction film layer L with an optical thickness of d / 4λ, c and d respectively represent the optical thickness regulating coefficients of the composite high-refraction material and the low-refraction material in the absorption-loss regulating layer, for regulating the electric field intensity and distribution at the center wavelength; A represents the incident medium layer, which is in contact with the outermost surface of the absorption-loss regulating layer.

2. The nanocomposite ultra-low absorbing low-loss thin film according to claim 1, wherein, The composite high-refraction 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-refraction film layer L is SiO2, YbF3 or MgF2.

3. The nanocomposite ultra-low absorbing low-loss thin film according to claim 1, wherein, The composite high-refraction film layer M is prepared by ion beam co-sputtering, magnetron co-sputtering, atomic layer co-deposition or electron beam double source co-evaporation to realize uniform nanoscale composite.

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

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

6. The nanocomposite ultra-low absorbing low-loss thin film according to any one of claims 1 to 4, wherein, The period number n of the composite high-reflection film layer ranges from 10 to 30.

Images