A short-wave infrared broadband antireflection film and its preparation method

Abstract

This invention provides a broadband antireflective coating for short-wave infrared and its preparation method, relating to the field of optical coating technology. The antireflective coating, from the surface of the glass substrate outwards, consists of: a Ta₂O₅ thin film layer, a SiO₂ thin film layer, another Ta₂O₅ thin film layer, another SiO₂ thin film layer, another Ta₂O₅ thin film layer, and a MgF₂ thin film layer. Ta₂O₅ is used as the high-refractive-index material, SiO₂ as the medium-to-low-refractive-index material, and MgF₂ as the outer low-refractive-index and protective material. A non-uniform thickness design achieves high-efficiency antireflection across a wide wavelength range. This film system exhibits an average transmittance of 99.6% and a minimum transmittance of 98.9% in the 800nm–1700nm wavelength range, with a passband width of 900nm, and possesses excellent mechanical strength, adhesion, and environmental stability. The method includes substrate cleaning, ion-assisted deposition of the Ta₂O₅ layer, electron beam evaporation of the SiO₂ and MgF₂ layers, and subsequent annealing treatment. The process is controllable and has good repeatability.

Description

Technical Field

[0001] This invention relates to the field of optical coating technology, specifically to a short-wave infrared broadband antireflection film and its preparation method. Background Technology

[0002] Antireflective coatings are key film systems for improving the transmittance of optical systems and reducing surface reflection loss. Covering the near-infrared and mid-infrared bands from 800nm ​​to 1700nm, they are commonly used in applications such as lidar, night vision imaging, and fiber optic sensing. Traditional antireflective coatings are mostly designed for narrowband or visible light, making it difficult to achieve high transmittance across this wide wavelength range.

[0003] In existing technologies, the antireflection band range of single-layer antireflection films is limited, and residual reflection remains high. Multilayer antireflection films can broaden the antireflection bandwidth by combining materials with different refractive indices, but increasing the number of layers often leads to problems such as stress accumulation, decreased adhesion, and poor environmental stability. In addition, materials commonly used in the near-infrared band, such as ZrO2, are prone to moisture absorption and crystallization, affecting the durability of the film. Therefore, Ta2O5 is selected as a high refractive index material. MgF2, on the other hand, is hard and non-hygroscopic, effectively improving the hardness of the coating and enhancing moisture resistance when used as an outer coating layer. Summary of the Invention

[0004] Therefore, this invention provides a broadband antireflection film for short-wave infrared and its preparation method to solve the above problems. The broadband antireflection film has extremely high transmittance, excellent mechanical properties and environmental stability in a wide wavelength range. The preparation method is simple, highly controllable and suitable for mass production.

[0005] This invention provides a broadband antireflective coating for short-wave infrared, comprising a double-sided six-layer film structure deposited on an optical glass substrate, wherein from the surface of the glass substrate outwards are a Ta2O5 thin film layer one, a SiO2 thin film layer one, a Ta2O5 thin film layer two, a SiO2 thin film layer three, a Ta2O5 thin film layer three, and a MgF2 thin film layer; Ta2O5 is used as a high refractive index material, SiO2 is used as a medium-low refractive index material, and MgF2 is used as an outer low refractive index and protective material, and broadband high-efficiency antireflection is achieved through non-uniform thickness design.

[0006] Furthermore, the physical thicknesses of each film layer are 38±1nm, 71±1nm, 175±1nm, 20±1nm, 72±1nm, and 204±1nm, respectively.

[0007] Furthermore, the physical thicknesses of each film layer are 38 nm, 71 nm, 172.5 nm, 20 nm, 72 nm, and 204.5 nm, respectively. The Ta2O5 film layer was prepared by ion-assisted deposition to improve the film density and optical stability; the SiO2 and MgF2 film layers were prepared by electron beam evaporation to ensure low absorption and high transmittance.

[0008] Furthermore, the antireflective coating is suitable for the wavelength range of 800nm ​​to 1700nm.

[0009] Furthermore, the glass substrate has a refractive index of 1.50 to 1.55.

[0010] The present invention also provides a method for preparing a short-wave infrared broadband antireflection film, which includes the following steps:

[0011] S1: Prepare three types of membrane materials: Ta2O5, SiO2, and MgF2. The Ta2O5 layer is deposited by ion-assisted deposition, and the SiO2 and MgF2 layers are evaporated by electron beam evaporation. All membrane materials are pretreated by drying and dehydration.

[0012] S2: The refractive index of the glass substrate is selected from 1.50 to 1.55. The glass substrate is ultrasonically cleaned sequentially with a mixture of ethanol, ether, and deionized water. After drying, the substrate is fixed in a fixture and placed in the coating machine cavity. The door is closed, a vacuum is drawn, and the substrate is gradually heated to a preset temperature of 280°C. After reaching the preset vacuum level, the three types of film materials are pre-melted to remove volatile impurities. The ion source is then activated to bombard the substrate surface with ions to enhance the surface activity of the substrate.

[0013] S3: The film is deposited layer by layer in the order of Sub / Ta2O5 / SiO2 / Ta2O5 / SiO2 / Ta2O5 / MgF2 / AIR. To improve the accuracy of control and ensure the antireflection performance and mechanical properties of the antireflection film, the deposition rate of Ta2O5 is 0.2~0.3nm / s, the deposition rate of SiO2 is 0.3~0.4nm / s, and the deposition rate of MgF2 is 0.2~0.4nm / s. The film thickness is monitored by quartz crystal oscillation method, and the thickness error of the core film layer (alternating Ta2O5 and SiO2 layers) is controlled within ±0.5nm.

[0014] S4: After the plating is completed, perform annealing treatment. Turn off the heater and wait for the coated element to cool slowly to 80°C in the vacuum chamber at a rate of ≤5°C / min. Then, fill the vacuum chamber with gas for air annealing. Raise the temperature to the target annealing temperature at a slow rate of 1 to 3°C / min and keep it constant for 3 to 4 hours. Turn off the heating power and let the coated part cool naturally to room temperature before opening the door to remove the part.

[0015] The prepared thin film layer was subjected to mechanical property testing. Two layers of dry, degreased gauze were wrapped around a rubber friction head, and the film layer was rubbed along the same trajectory under a pressure of 4.9 N for 50 cycles. No scratches or damage were observed on the film layer. Adhesive tape with a width of 2 cm and a peel strength ≥ 2.94 N / cm² was adhered to the surface of the film layer. After the tape was quickly pulled up from the edge of the part in a direction perpendicular to the surface, the film layer did not peel off or show any damage, proving that the prepared thin film layer has good mechanical strength.

[0016] The present invention has the following advantages over the prior art:

[0017] 1. In the process of preparing multilayer composite antireflective films, it was found that excessive film stress can easily cause film cracking, edge curling, and shrinkage; thermal stress and internal stress are the main causes of film stress. The multilayer composite antireflective film prepared by the method of this invention incorporates an annealing treatment step at the end, which solves the problems of stress matching and adhesion of the film layers while maintaining the antireflective effect. This film system has an average transmittance of 99.6% and a minimum transmittance of 98.9% in the 800nm ​​to 1700nm wavelength range, a passband width of 900nm, and excellent mechanical strength. Attached Figure Description

[0018] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0019] Figure 1 : A schematic diagram of the antireflective membrane structure prepared by the present invention;

[0020] Figure 2 : Transmittance curve of the antireflection membrane prepared by this invention;

[0021] Figure 3 Transmittance curve of glass substrate before coating:

[0022] Explanation of reference numerals in the attached figures:

[0023] 1. MgF2 thin film layer; 2. Ta2O5 thin film layer three; 3. SiO2 thin film layer two; 4. Ta2O5 thin film layer two; 5. SiO2 thin film layer one; 6. Ta2O5 thin film layer one; 7. Glass substrate. Detailed Implementation

[0024] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] Example 1

[0026] Reference Figure 1 This embodiment provides a broadband antireflective coating for short-wave infrared radiation, comprising a double-sided six-layer film structure deposited on an optical glass substrate 7. From the inside out on both sides of the glass substrate 7, the layers are: Ta2O5 thin film layer 6, SiO2 thin film layer 5, Ta2O5 thin film layer 4, SiO2 thin film layer 3, Ta2O5 thin film layer 2, and MgF2 thin film layer 1. The glass substrate 7 is a BAK2 glass substrate.

[0027] The physical thicknesses of each film layer are, in order, 38±1 nm, 71±1 nm, 175±1 nm, 20±1 nm, 72±1 nm, and 204±1 nm. The preferred physical thicknesses are 38 nm, 71 nm, 172.5 nm, 20 nm, 72 nm, and 204.5 nm. The antireflective coating is suitable for the wavelength range of 800 nm to 1700 nm. The refractive index of the glass substrate 7 is 1.50 to 1.55.

[0028] Example 2

[0029] This embodiment provides a method for preparing a short-wave infrared broadband antireflection film, which is carried out according to the following steps:

[0030] S1: Prepare three types of membrane materials: Ta2O5, SiO2, and MgF2. The Ta2O5 layer is deposited by ion-assisted deposition, and the SiO2 and MgF2 layers are evaporated by electron beam evaporation. All membrane materials are pretreated by drying and dehydration.

[0031] S2: Select BAK2 optical glass as the substrate. The glass substrate is ultrasonically cleaned sequentially using a mixture of ethanol, ether, and deionized water. The dried substrate is fixed in a fixture and placed in the coating machine cavity. The door is closed, a vacuum is drawn, and the substrate is gradually heated to a preset temperature of 280°C. After reaching the preset vacuum level, the three types of film materials are pre-melted to remove volatile impurities. The ion source is then activated to bombard the substrate surface with ions to enhance the surface activity of the substrate.

[0032] S3: The film is deposited layer by layer in the order of Sub / Ta2O5 / SiO2 / Ta2O5 / SiO2 / Ta2O5 / MgF2 / AIR. To improve the accuracy of control and ensure the antireflection performance and mechanical properties of the antireflection film, the deposition rate of Ta2O5 is 0.2 to 0.3 nm / s, the deposition rate of SiO2 is 0.3 to 0.4 nm / s, and the deposition rate of MgF2 is 0.2 to 0.4 nm / s. The film thickness is monitored by the quartz crystal oscillation method, and the thickness error of the core film layer (alternating Ta2O5 and SiO2 layers) is controlled within ±0.5 nm.

[0033] S4: After the plating is completed, perform annealing treatment. Turn off the heater and wait for the coated element to cool slowly to 80°C in the vacuum chamber at a rate of ≤5°C / min. Then, fill the vacuum chamber with gas for air annealing. Raise the temperature to the target annealing temperature at a slow rate of 1 to 3°C / min and keep it constant for 3 to 4 hours. Turn off the heating power and let the coated part cool naturally to room temperature before opening the door to remove the part.

[0034] The prepared thin film layer was subjected to mechanical property testing. Two layers of dry, degreased gauze were wrapped around a rubber friction head, and the film layer was rubbed along the same trajectory under a pressure of 4.9 N for 35 cycles. No scratches or other damage were observed on the film layer. Adhesive tape with a width of 2 cm and a peel strength ≥ 2.94 N / cm² was adhered to the surface of the film layer. After the tape was quickly pulled up from the edge of the part in a direction perpendicular to the surface, the film layer did not peel off or show any damage, proving that the prepared thin film layer has good mechanical strength.

[0035] like Figure 2 The transmittance curve of the antireflection membrane prepared in this invention; Figure 3 The graph shows the transmittance of the glass substrate before coating. By comparison, it can be found that the antireflective coating prepared by this invention has an average transmittance of 99.6% in the 800nm ​​to 1700nm band, a minimum transmittance of 98.9%, a passband width of 900nm, and excellent mechanical strength.

[0036] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A broadband antireflective coating for short-wave infrared radiation, characterized in that, It includes a double-sided six-layer film structure deposited on an optical glass substrate (7), which consists of Ta2O5 thin film layer 1 (6), SiO2 thin film layer 1 (5), Ta2O5 thin film layer 2 (4), SiO2 thin film layer 2 (3), Ta2O5 thin film layer 3 (2), and MgF2 thin film layer (1) from the two sides of the glass substrate (7) outward.

2. The broadband antireflective coating for short-wave infrared radiation according to claim 1, characterized in that, The physical thicknesses of each film layer are 38±1nm, 71±1nm, 175±1nm, 20±1nm, 72±1nm, and 204±1nm, respectively.

3. The broadband antireflective coating for short-wave infrared radiation according to claim 2, characterized in that, The physical thicknesses of each film layer are 38nm, 71nm, 172.5nm, 20nm, 72nm, and 204.5nm, respectively.

4. The broadband antireflective coating for short-wave infrared radiation according to claim 3, characterized in that, Antireflective coatings are suitable for wavelengths from 800nm ​​to 1700nm.

5. The short-wave infrared broadband antireflection film according to claim 4, characterized in that, The glass substrate (7) has a refractive index of 1.50 to 1.

55.

6. A method for preparing a short-wave infrared broadband antireflection film, applied to the broadband antireflection film according to any one of claims 1 to 6, characterized in that, Includes the following steps: S1: Prepare three types of membrane materials: Ta2O5, SiO2, and MgF2. The Ta2O5 layer is deposited by ion-assisted deposition, and the SiO2 and MgF2 layers are evaporated by electron beam evaporation. All membrane materials are pretreated by drying and dehydration. S2: Clean the glass substrate; fix the dried substrate in the tooling fixture, place it in the coating machine cavity, close the door, evacuate and heat it to the preset temperature; after reaching the preset vacuum level, pre-melt the three types of film materials to remove volatile impurities; start the ion source to bombard the substrate surface with ions to enhance the surface activity of the substrate. S3: The film is deposited layer by layer in the order of Sub / Ta2O5 / SiO2 / Ta2O5 / SiO2 / Ta2O5 / MgF2 / AIR. The film thickness is monitored in real time using the quartz crystal oscillation method to ensure that the thickness error of each layer is ≤±0.5nm. S4: After plating is completed, annealing is performed, followed by cooling and opening the door to retrieve the parts.

7. The preparation method according to claim 6, characterized in that, In step S2, ultrasonic cleaning is used to clean the glass substrate. After drying, the substrate is placed in a vacuum and then heated to 280°C.

8. The preparation method according to claim 6, characterized in that, In step S3, the films are deposited sequentially according to the film layer order. To improve the accuracy of control and ensure the antireflection performance and mechanical properties of the antireflection film, the deposition rate of Ta2O5 is 0.2 to 0.3 nm / s, the deposition rate of SiO2 is 0.3 to 0.4 nm / s, and the deposition rate of MgF2 is 0.2 to 0.4 nm / s. The film thickness is monitored using the quartz crystal oscillation method, and the thickness error of the core film layer, including the alternating layers of Ta2O5 and SiO2, is controlled within ±0.5 nm.

9. The preparation method according to claim 6, characterized in that, In step S4, after step S3 is completed, the heater is turned off. When the coated element is slowly cooled to 80°C in the vacuum chamber at a rate of ≤5°C / min, the vacuum chamber is filled with gas for air annealing. The temperature is increased to the target annealing temperature at a slow rate of 1 to 3°C / min and kept constant for 3 to 4 hours. The heating power is turned off, and the coated part is allowed to cool naturally to room temperature before the door is opened and the part is taken out.

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