Ultraviolet band antireflection film and preparation method thereof, and ultraviolet antireflection film element

Abstract

The invention belongs to the technical field of optical elements, and particularly relates to an ultraviolet band antireflection film, a preparation method thereof and an ultraviolet antireflection film element. The film layer structure of the ultraviolet band antireflection film provided by the invention comprises a first hafnium oxide layer, a first silicon oxide layer, a second hafnium oxide layer, a second silicon oxide layer, a third hafnium oxide layer and a third silicon oxide layer which are sequentially stacked, wherein the first hafnium oxide layer is in contact with the surface of a substrate; and the total thickness of the first hafnium oxide layer, the second hafnium oxide layer and the third hafnium oxide layer accounts for 5-10% of the total thickness of the film layer structure. The ultraviolet band antireflection film provided by the invention has the characteristics of ultraviolet resistance and high power, is high in wavelength drift resistance, and can meet the requirements of high transmittance and no damage trace on the appearance under the condition of continuous long-time irradiation of a picosecond pulse laser; meanwhile, the film layer is weak and small in absorption, the yield is high, and industrial large-scale stable preparation can be met.

Description

Technical Field

[0001] This invention belongs to the field of optical element technology, specifically relating to an ultraviolet antireflection film and its preparation method, and an ultraviolet antireflection film element. Background Technology

[0002] Antireflective coatings are widely used in various optical components. Their main purpose is to reduce the surface reflectivity of the component and improve its transmittance. Although antireflective coatings are relatively basic, they have the most widespread applications. Therefore, there is a great deal of research on antireflective coatings, especially in the visible or near-infrared bands, including research on low-absorption, high-power antireflective coatings, etc. However, research on ultraviolet antireflective coatings is relatively limited. Among these studies, the damage resistance of a 266nm antireflective coating under a 7ns pulse width condition was investigated, and the laser damage resistance threshold was approximately 6J / cm. 2 With the continuous development of the laser industry, picosecond pulsed ultrafast lasers are increasingly used in products such as field lenses and beam expanders, placing higher demands on the damage resistance of optical thin films, especially in the area of ​​high-power ultraviolet antireflection films. Therefore, developing a method for preparing high-power ultraviolet antireflection films has significant research value and practical application value. Summary of the Invention

[0003] The purpose of this invention is to provide an antireflective film in the ultraviolet band and its preparation method, as well as an ultraviolet antireflective film element. The ultraviolet antireflective film provided by this invention has the characteristics of high ultraviolet power resistance and strong anti-wavelength drift capability. It can meet the requirements of high transmittance and no damage marks on the appearance under continuous long-term irradiation by picosecond pulsed lasers. At the same time, the film layer has weak absorption and low yield, which can meet the requirements of stable mass production in industrial applications.

[0004] To achieve the above objectives, the present invention provides the following technical solution: This invention provides an antireflective coating for the ultraviolet band. The coating structure includes a first hafnium oxide layer, a first silicon oxide layer, a second hafnium oxide layer, a second silicon oxide layer, a third hafnium oxide layer, and a third silicon oxide layer stacked sequentially. The first hafnium oxide layer is in contact with the surface of a substrate. The total thickness of the first hafnium oxide layer, the second hafnium oxide layer, and the third hafnium oxide layer accounts for 5-10% of the total thickness of the coating structure.

[0005] Preferably, the thickness of the first hafnium oxide layer is 4~8nm, the thickness of the first silicon oxide layer is 146~194nm, the thickness of the second hafnium oxide layer is 9~15nm, the thickness of the second silicon oxide layer is 97~121nm, the thickness of the third hafnium oxide layer is 11~13nm, and the thickness of the third silicon oxide layer is 75~81nm.

[0006] Preferably, the total thickness of the first hafnium oxide layer, the second hafnium oxide layer, and the third hafnium oxide layer is 32~36 nm; the total thickness of the film structure is 351~375 nm.

[0007] Preferably, the thickness of the first hafnium oxide layer is 7-8 nm, the thickness of the first silicon oxide layer is 146-155 nm, the thickness of the second hafnium oxide layer is 13-15 nm, the thickness of the second silicon oxide layer is 97-103 nm, the thickness of the third hafnium oxide layer is 12-13 nm, and the thickness of the third silicon oxide layer is 76-81 nm.

[0008] Preferably, the total thickness of the first hafnium oxide layer, the second hafnium oxide layer and the third hafnium oxide layer is 24~29 nm, and the total thickness of the film structure is 398~424 nm.

[0009] Preferably, the thickness of the first hafnium oxide layer is 4-5 nm, the thickness of the first silicon oxide layer is 184-194 nm, the thickness of the second hafnium oxide layer is 9-11 nm, the thickness of the second silicon oxide layer is 115-121 nm, the thickness of the third hafnium oxide layer is 11-13 nm, and the thickness of the third silicon oxide layer is 75-80 nm.

[0010] This invention provides a method for preparing the ultraviolet antireflective coating described in the above technical solution, comprising the following steps: Based on the film material, optical band, and optical properties of the ultraviolet band antireflection film, film system design software is used to design the film system and obtain the film system design results of the ultraviolet band antireflection film. A first hafnium oxide layer, a first silicon oxide layer, a second hafnium oxide layer, a second silicon oxide layer, a third hafnium oxide layer, and a third silicon oxide layer are sequentially deposited on the surface of the substrate according to the film system design results to obtain the ultraviolet band antireflection film.

[0011] Preferably, the deposition is performed using a vacuum evaporation deposition method; the deposition conditions include: initial vacuum degree ≤ 1.8E-3Pa; substrate heating temperature of 180~300℃; deposition rate of the first hafnium oxide layer, the second hafnium oxide layer and the third hafnium oxide layer of 0.1~0.25nm / s, and deposition rate of the first silicon oxide layer, the second silicon oxide layer and the third silicon oxide layer of 0.3~0.7nm / s.

[0012] The present invention provides an ultraviolet antireflection film element, comprising a substrate and an antireflection film disposed on both surfaces of the substrate; the antireflection film is the ultraviolet band antireflection film described in the above technical solution or the ultraviolet band antireflection film prepared by the preparation method described in the above technical solution.

[0013] Preferably, the substrate is ultraviolet fused silica glass; the substrate is cylindrical in shape, and the dimensions of the substrate are: a diameter of 25.4 mm and a thickness of 0.6~6 mm.

[0014] This invention provides an antireflective coating for the ultraviolet (UV) band. The coating structure comprises a first hafnium oxide layer, a first silicon oxide layer, a second hafnium oxide layer, a second silicon oxide layer, a third hafnium oxide layer, and a third silicon oxide layer stacked sequentially. The first hafnium oxide layer is in contact with the surface of the substrate. The total thickness of the first, second, and third hafnium oxide layers accounts for 5-10% of the total thickness of the coating structure. This invention uses hafnium oxide in combination with low-refractive-index silicon oxide (SiO2), and optimizes the coating structure to 6 layers. The total thickness of the hafnium oxide layers (first, second, and third layers) is strictly controlled to account for 5-10% of the total thickness, thereby exhibiting high UV resistance and strong anti-wavelength drift capability. It can meet the requirements of high transmittance and no visible damage under continuous long-term irradiation by picosecond pulsed lasers. Compared with existing technologies, the present invention has the following beneficial effects: The ultraviolet antireflection film provided by the present invention can withstand long-term testing by a high-power picosecond pulsed ultrafast laser (355nm, pulse width: <10ps, single pulse: 120μJ, average power 20W, spot diameter approximately 6mm). The high-power antireflection film has significant advantages: 1. Strong resistance to wavelength drift (the wavelength range that meets the requirement of maximum reflectivity less than 0.25% reaches 22nm, far exceeding the 15nm required for normal mass production); 2. Strong resistance to damage testing, capable of withstanding continuous irradiation by a picosecond pulsed laser for more than 15 days (approximately 360h) with a transmittance >98% and no visible damage; 3. Low weak absorption, with weak absorption <20ppm at 355nm and 1.91ppm at 1064nm; 4. Temperature rise of only 0.2℃ under room temperature conditions, far superior to <3℃ of existing technologies.

[0015] Meanwhile, the ultraviolet antireflection membrane provided by this invention has low absorption and high yield, which can meet the requirements for stable mass production in industrial applications. Attached Figure Description

[0016] Figure 1 The curve diagram for the three-layer membrane system in Comparative Example 1; Figure 2 This is a graph showing the actual deposition curves of the three-layer film system in Comparative Example 1; Figure 3 This is the optical path diagram for damage resistance testing in this invention; Figure 4 Damage diagram of the antireflection membrane with a three-layer membrane structure prepared in Comparative Example 1; Figure 5 The design curves for the membrane system in Comparative Example 2 are shown. Figure 6This is a graph showing the actual deposition curves of the film system in Comparative Example 2; Figure 7 The image shows the damage to the antireflection membrane prepared in Comparative Example 2. Figure 8 This is a graph showing the membrane system design in Example 1; Figure 9 This is a graph showing the actual deposition curves of the film system in Example 1; Figure 10 Damage diagram of the antireflection membrane prepared in Example 1; Figure 11 This is a graph showing the membrane system design in Example 2. Detailed Implementation

[0017] This invention provides an antireflective coating for the ultraviolet band. The coating structure includes a first hafnium oxide layer, a first silicon oxide layer, a second hafnium oxide layer, a second silicon oxide layer, a third hafnium oxide layer, and a third silicon oxide layer stacked sequentially. The first hafnium oxide layer is in contact with the surface of a substrate. The total thickness of the first hafnium oxide layer, the second hafnium oxide layer, and the third hafnium oxide layer accounts for 5-10% of the total thickness of the coating structure.

[0018] In this invention, unless otherwise specified, all raw materials / components used in the preparation are commercially available products well-known to those skilled in the art. The damage testing conditions for the ultraviolet antireflection film in this invention are: 355nm, pulse width <10ps (picosecond), single pulse energy 120μJ, average power 20W, and spot diameter approximately 6mm. The test results meet the following requirements: after continuous testing for 15 days (approximately 360 hours), the transmittance is greater than 98%, and there is no visible damage. Analysis of this invention reveals that the ultraviolet antireflection film element has a structure in which the ultraviolet antireflection film is deposited on both sides of the substrate.

[0019] In this invention, the total thickness of the film structure is the total thickness of the first hafnium oxide layer, the first silicon oxide layer, the second hafnium oxide layer, the second silicon oxide layer, the third hafnium oxide layer, and the third silicon oxide layer. Preferably, the total thickness of the first hafnium oxide layer, the second hafnium oxide layer, and the third hafnium oxide layer accounts for 6-9.5% of the total thickness of the film structure, more preferably 6.46-9.39%.

[0020] In this invention, the total thickness of the first hafnium oxide layer, the second hafnium oxide layer, and the third hafnium oxide layer is preferably 24-36 nm. The total thickness of the film structure is preferably 342-432 nm. In this invention, the thickness of the first hafnium oxide layer is preferably 4-8 nm. The thickness of the first silicon oxide layer is preferably 146-194 nm. The thickness of the second hafnium oxide layer is preferably 9-15 nm. The thickness of the second silicon oxide layer is preferably 97-121 nm. The thickness of the third hafnium oxide layer is preferably 11-13 nm. The thickness of the third silicon oxide layer is preferably 75-81 nm.

[0021] In this invention, the total thickness of the first hafnium oxide layer, the second hafnium oxide layer, and the third hafnium oxide layer is preferably 32-36 nm. The total thickness of the film structure is preferably 351-375 nm. In this invention, the thickness of the first hafnium oxide layer is preferably 7-8 nm. The thickness of the first silicon oxide layer is preferably 146-155 nm. The thickness of the second hafnium oxide layer is preferably 13-15 nm. The thickness of the second silicon oxide layer is preferably 97-103 nm. The thickness of the third hafnium oxide layer is preferably 12-13 nm. The thickness of the third silicon oxide layer is preferably 76-81 nm.

[0022] In this invention, the total thickness of the first hafnium oxide layer, the second hafnium oxide layer, and the third hafnium oxide layer is preferably 24-29 nm. The total thickness of the film structure is preferably 398-424 nm. In this invention, the thickness of the first hafnium oxide layer is preferably 4-5 nm. The thickness of the first silicon oxide layer is preferably 184-194 nm. The thickness of the second hafnium oxide layer is preferably 9-11 nm. The thickness of the second silicon oxide layer is preferably 115-121 nm. The thickness of the third hafnium oxide layer is preferably 11-13 nm. The thickness of the third silicon oxide layer is preferably 75-80 nm.

[0023] In this invention, the total thickness of the first hafnium oxide layer, the second hafnium oxide layer, and the third hafnium oxide layer is preferably 33.25~34.94 nm. The total thickness of the film structure is preferably 353.99~372.05 nm. In this invention, the thickness of the first hafnium oxide layer is preferably 7.26~7.63 nm. The thickness of the first silicon oxide layer is preferably 146.92~154.42 nm. The thickness of the second hafnium oxide layer is preferably 13.65~14.35 nm. The thickness of the second silicon oxide layer is preferably 97.06~102.01 nm. The thickness of the third hafnium oxide layer is preferably 12.33~12.96 nm. The thickness of the third silicon oxide layer is preferably 76.77~80.68 nm.

[0024] In this invention, the total thickness of the first hafnium oxide layer, the second hafnium oxide layer, and the third hafnium oxide layer is preferably 25.96~27.23 nm. The total thickness of the film structure is preferably 401.62~421.3 nm. In this invention, the thickness of the first hafnium oxide layer is preferably 4.34~4.55 nm. The thickness of the first silicon oxide layer is preferably 184.22~193.06 nm. The thickness of the second hafnium oxide layer is preferably 9.64~10.1 nm. The thickness of the second silicon oxide layer is preferably 115.46~121 nm. The thickness of the third hafnium oxide layer is preferably 11.98~12.56 nm. The thickness of the third silicon oxide layer is preferably 75.98~79.63 nm.

[0025] This invention provides a method for preparing the ultraviolet antireflective coating described in the above technical solution, comprising the following steps: Based on the film material, optical band, and optical properties of the ultraviolet band antireflection film, film system design software is used to design the film system and obtain the film system design results of the ultraviolet band antireflection film. A first hafnium oxide layer, a first silicon oxide layer, a second hafnium oxide layer, a second silicon oxide layer, a third hafnium oxide layer, and a third silicon oxide layer are sequentially deposited on the surface of the substrate according to the film system design results to obtain the ultraviolet band antireflection film.

[0026] This invention, based on the film material, optical band, and optical properties of the ultraviolet antireflection film, uses film system design software to design the film system, obtaining the film system design result of the ultraviolet antireflection film. In this invention, the optical band can be the 355nm band. The optical properties include: R... max <0.25%. Transmittance greater than 99% (T>99%). The film system design software includes TFCalc optical thin film design software or Essential Macleod optical thin film design software. The film system design results of the ultraviolet antireflective film include the thickness of each layer and the total thickness.

[0027] After obtaining the film system design results of the ultraviolet band antireflection film, the present invention sequentially deposits a first hafnium oxide layer, a first silicon oxide layer, a second hafnium oxide layer, a second silicon oxide layer, a third hafnium oxide layer, and a third silicon oxide layer on the surface of the substrate according to the film system design results to obtain the ultraviolet band antireflection film.

[0028] In this invention, the substrate is preferably ultraviolet-fused silica glass. The substrate can be cylindrical. The dimensions of the substrate are: a diameter preferably of 25.4 mm, and a thickness preferably of 0.6~6 mm, which is 5 mm in the embodiment. The transparent region of the substrate is in the range of 185~2100 nm. The transparent region of the ultraviolet-fused silica glass has advantages such as high transmittance, low absorption, and high chemical stability.

[0029] In this invention, prior to the plating process, the substrate is preferably further subjected to ion source cleaning. Preferably, the substrate is placed in a collar, and the collar containing the substrate is placed on a perforated fixture on the machine; then ion source cleaning is performed. This invention preferably improves the adhesion of the ultraviolet antireflective film on the substrate surface through ion source cleaning. The vacuum degree of the ion source cleaning is preferably ≤1.8E-3Pa, the time is preferably 2~5 min, more preferably 3 min; the heating temperature of the substrate during ion source cleaning is preferably 180~300℃. By controlling the heating temperature of the substrate to 180~300℃ during ion source cleaning, this invention can reduce ion absorption of the substrate during the ion source cleaning process. In this invention, the conditions for ion source cleaning preferably include: an ion source voltage of 1000~1100V; an ion source current of 1000~1100mA; and a bias voltage of 900~950V. The gases used for cleaning the ion source preferably include ion source oxygen, ion source argon, and neutralizer argon. The flow rate of the ion source oxygen is preferably 50-60 SCCM. The flow rate of the ion source argon is preferably 0 SCCM. The flow rate of the neutralizer argon is preferably 8-10 SCCM.

[0030] In this invention, the deposition is performed after the ion source cleaning is completed. Preferably, the deposition is performed using a vacuum evaporation deposition method. The ultraviolet antireflection film is deposited using a vacuum evaporation deposition machine. The deposition process is monitored for film velocity and thickness using a crystal oscillator. The auxiliary configuration used in this invention includes: a molecular pump, a radio frequency ion source, and a Nanjing Shibuya electron gun.

[0031] In this invention, during the plating process, the substrate is preferably placed within a collar, and the collar containing the substrate is placed on a perforated umbrella-shaped fixture on the machine. The plating conditions preferably include: an initial vacuum degree preferably ≤1.8E-3Pa; and a substrate heating temperature preferably 180~300℃.

[0032] In this invention, the raw material for preparing the first hafnium oxide layer, the second hafnium oxide layer, and the third hafnium oxide layer is metallic hafnium. This invention uses metallic hafnium (Hf) as the raw material when preparing the first hafnium oxide layer, the second hafnium oxide layer, and the third hafnium oxide layer, abandoning the conventional use of HfO2 as the raw material. This effectively avoids the problem of uneven defects in the film layer during the deposition process, which in turn affects its poor damage resistance.

[0033] In this invention, the film formation rates of the first hafnium oxide layer, the second hafnium oxide layer, and the third hafnium oxide layer are preferably 0.1~0.25 nm / s. The deposition conditions for the first, second, and third hafnium oxide layers preferably include: an ion source voltage of 1000~1100V; an ion source current of 900~950mA; and a bias voltage of 750~800V. The gas used for cleaning the ion source preferably includes ion source oxygen, ion source argon, and neutralizer argon. The flow rate of the ion source oxygen is preferably 80~90 SCCM. The flow rate of the ion source argon is preferably 0 SCCM. The flow rate of the neutralizer argon is preferably 8~10 SCCM. The oxygen filling rate of the APC is preferably 50~55 SCCM.

[0034] In this invention, the film formation rate of the first silicon oxide layer, the second silicon oxide layer, and the third silicon oxide layer is preferably 0.3~0.7 nm / s, and in the embodiment, it can be 0.6 nm / s. The deposition conditions for the first silicon oxide layer, the second silicon oxide layer, and the third silicon oxide layer preferably include: an ion source voltage preferably of 900~950V; an ion source current preferably of 800~850mA; and a bias voltage preferably of 600~650V. The gas used for cleaning the ion source preferably includes ion source oxygen, ion source argon, and neutralizer argon. The flow rate of the ion source oxygen is preferably 30~35 SCCM. The flow rate of the ion source argon is preferably 10~15 SCCM. The flow rate of the neutralizer argon is preferably 8~10 SCCM. APC oxygenation is preferably 0 SCCM.

[0035] The present invention provides an ultraviolet antireflection film element, comprising a substrate and an antireflection film disposed on both surfaces of the substrate; the antireflection film is the ultraviolet band antireflection film described in the above technical solution or the ultraviolet band antireflection film prepared by the preparation method described in the above technical solution.

[0036] In this invention, the substrate is preferably ultraviolet-fused silica glass. The substrate can be cylindrical. The dimensions of the substrate are: a diameter preferably of 25.4 mm, and a thickness preferably of 0.6~6 mm, which is 5 mm in the embodiment. The transparent region of the substrate is in the range of 185~2100 nm. The transparent region of the ultraviolet-fused silica glass has advantages such as high transmittance, low absorption, and high chemical stability.

[0037] In this invention, the ultraviolet antireflective coating is disposed on the two bottom surfaces of the cylindrical substrate, while the sides of the cylindrical substrate are not coated.

[0038] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0039] Comparative Example 1 1. Based on optical specifications, 355nm, R max <0.25%. A three-layer antireflection film system was designed, with the following structural sequence: silicon oxide layer (12.93 nm) – hafnium oxide layer (23.78 nm) – silicon oxide layer (73.67 nm). The total thickness of the hafnium oxide layer is 23.78 nm, the total thickness of the silicon oxide layer is 86.6 nm, and the total film thickness is 110.38 nm. The hafnium oxide layer thickness accounts for approximately 21.54% of the total thickness (23.78 / 110.38). The design curve of the three-layer antireflection film system provided in this comparative example is shown below. Figure 1 As shown. By Figure 1 It can be seen that the wavelength range with reflectivity less than 0.25% is approximately 346~374nm, about 28nm. From Figure 1 From a design perspective, it not only meets optical specifications but also satisfies wide wavelength requirements, resulting in stronger resistance to wavelength drift. Preliminary design assessment indicates it meets the requirements.

[0040] 2. Film deposition, specific parameters are as follows: Domestic evaporation deposition machine, configuration: molecular pump, RF ion source, Nanjing Shibuya electron gun. Film deposition conditions: initial vacuum ≤1.8E-3Pa, heating: 260℃, ion source cleaning: 3 minutes, 180s; Hafnium metal (Hf) is used for deposition, and oxygen is used to ultimately form hafnium oxide (HfO2). The ion source oxygenation is 80 SCCM, and the APC oxygenation is 55 SCCM. The purpose is to make the hafnium metal reaction more complete, reduce absorption, and improve damage resistance. Its deposition rate is set to 0.1 nm / s. The silicon oxide (SiO2) deposition rate is 0.6 nm / s. The power of the ion source cleaning and deposition processes is relatively high to reduce substrate absorption and improve film density, avoiding internal defects in the film due to insufficient energy, which would affect laser damage resistance. Detailed process parameters are shown in Table 1. After coating the two bottom surfaces of the substrate, the reflectance was measured using an MSP-100B-UV reflectance meter to obtain the actual reflectance curves of the three-layer film system in Comparative Example 1, as shown below. Figure 2 As shown. It meets optical specifications, with a reflectivity of less than 0.25% in the range of approximately 348~371nm, about 23nm, which is sufficient for stable production.

[0041] Table 1 Film-forming process parameters in Comparative Example 1

[0042] 3. The double-sided coated window was subjected to laser damage resistance testing using a domestically produced 355nm picosecond ultrafast laser. Specific parameters were set as follows: 355nm, pulse width <10ps (picosecond), single pulse energy 120μJ, average power 20W, and spot diameter approximately 6mm. Calculations showed that the repetition frequency = average power / single pulse energy = 20W / 120μJ = 166kHz. Given the extremely high repetition frequency and the picosecond ultrafast laser, the laser is highly destructive. The optical path for the damage resistance test is as follows: Figure 3 Transmittance data was collected twice daily. As the testing period progressed, the transmittance gradually decreased, falling below 98% in less than 60 hours and dropping to 95.09% after 7 days. Transmittance data was collected using a power meter, and detailed transmittance data are shown in Table 2. The test piece was simultaneously removed for visual inspection; blackening marks were visible to the naked eye, and significant damage was observed under a microscope. Figure 4 .

[0043] Table 2. Damage resistance transmittance test data of the three-layer membrane system in Comparative Example 1

[0044] 4. Cause Analysis: The above-mentioned process offers superior damage resistance in terms of ion source energy intensity, substrate material, and membrane material. This invention uses the controlled variable method, making changes only to the membrane system design for verification.

[0045] Comparative Example 2 1. While maintaining optical specifications and unchanged film materials, an optimized design was implemented based on Comparative Example 1, adjusting the number and thickness of film layers. A six-layer film system was designed, with the following structural sequence: hafnium oxide layer (20.47 nm) – silicon oxide layer (14.22 nm) – hafnium oxide layer (47.37 nm) – silicon oxide layer (48.67 nm) – hafnium oxide layer (17.6 nm) – silicon oxide layer (86.6 nm). The total thickness of the hafnium oxide layer is 85.44 nm, the total thickness of the silicon oxide layer is 149.49 nm, and the total film thickness is 234.93 nm. The hafnium oxide layer thickness accounts for approximately 36.37% of the total thickness (85.44 / 234.93). The film system design curve for this comparative example is shown below. Figure 5 ,Depend on Figure 5 It can be seen that the wavelength range with reflectivity less than 0.25% is approximately 342~368nm, about 26nm. From a design perspective, the optical effect and resistance to wavelength drift are similar to Comparative Example 1. The only difference between this comparative example and Comparative Example 1 is the increased number and thickness percentage of hafnium oxide layers.

[0046] 2. The plating process and procedure are the same as in Comparative Example 1, and the obtained plating curve meets the optical requirements, as shown in the figure. Figure 6 As shown.

[0047] 3. The damage test of the six-layer film system in Comparative Example 2 was conducted using the same system as in Comparative Example 1. Detailed data are shown in Table 3 below.

[0048] The initial transmittance was 99.68%, higher than that of Comparative Example 1 (99.2%). This is because the six-layer film system of Comparative Example 2 and its reflectance at 355 nm in the actual deposition curve are both lower than those of the three-layer film system of Comparative Example 1, resulting in higher transmittance. However, as the testing time progressed, the transmittance of the six-layer film system prepared in Comparative Example 2 also gradually decreased. Within 84 hours, the transmittance was already below 98%, decreasing to 96.88% after 4 days, and further decreasing to 94.73% after 7 days, approximately 180 hours later. Simultaneously, the test piece prepared in Comparative Example 2 was removed for visual inspection. Under a microscope, obvious damage was observed, such as... Figure 7 As stated above.

[0049] Table 3. Test data on the damage resistance transmittance of the film deposited in Comparative Example 2.

[0050] 4. Cause Analysis: Comparison of damage test data revealed that Comparative Example 2, by increasing the number of film layers and the proportion of hafnium oxide layer thickness, achieved a slightly higher initial transmittance, and the transmittance decreased slowly in the first few days. However, over time, the transmittance essentially dropped to the same level. The analysis is as follows: Increasing the hafnium oxide layer thickness can improve damage resistance to some extent. However, increasing the thickness of the hafnium oxide layer increases the probability of insufficient oxidation during the deposition process, leading to gap defects. This results in a slow decrease in transmittance in the first few days, followed by a rapid decrease in transmittance due to the numerous defects causing intense internal heating and burn-through during laser irradiation. Therefore, this invention further shifts its approach to verify the hypothesis. While ensuring optical specifications, the thickness proportion of the hafnium oxide layer is optimized from a design perspective.

[0051] Example 1 1. Under the premise of meeting optical specifications and keeping the film material unchanged, the film system was optimized by considering reducing the proportion of the total thickness of the hafnium oxide layer. After adjustment, Comparative Example 2 also obtained a six-layer film system with the following structural sequence: hafnium oxide layer (7.445nm) – silicon oxide layer (150.67nm) – hafnium oxide layer (14nm) – silicon oxide layer (99.535nm) – hafnium oxide layer (12.645nm) – silicon oxide layer (78.725nm). The total thickness of the hafnium oxide layer is approximately 34.09nm, and the total film thickness is 363.02nm. The proportion of the hafnium oxide layer thickness to the total thickness is 34.09 / 363.02, approximately 9.39%. The film system design curve of this embodiment is shown below. Figure 8 ,Depend on Figure 8 It can be seen that the wavelength range with reflectivity less than 0.25% is approximately 345~364nm, or about 19nm.

[0052] 2. The plating process parameters are the same as those in Comparative Example 1, and the actual plating curve is as follows: Figure 9 .Depend on Figure 9 It can be seen that the wavelength range with reflectivity less than 0.25% is approximately 344-366nm, about 22nm, and has strong resistance to wavelength drift. (Generally, for mass production with single-point requirements, ≥15nm is sufficient).

[0053] 3. The UV antireflection film element coated in Example 1 was subjected to a damage resistance test, using the same method as Comparative Examples 1 and 2. The final transmittance data is shown in Table 4. Analysis of the transmittance data shows that after 15 days of testing, although the transmittance fluctuated (due to testing error), it remained around 99% overall, with the lowest set at 98.66%, meeting the required specification: transmittance greater than 98% after continuous testing for half a month. Upon inspection, no damage was observed on the surface or under a microscope. The results of visual and microscopic observations after the damage test are as follows: Figure 10 As shown.

[0054] Table 4. Damage resistance transmittance test data of the membrane prepared in Example 1

[0055] 4. Weak Absorption and Temperature Rise Test: The high-power UV antireflection film deposited in Example 1 met both optical specifications and damage resistance standards. Therefore, its weak absorption rate and temperature rise under 355nm laser irradiation at room temperature were tested. Weak absorption was tested using a weak absorption meter from Hefei Zhichang. The area scanning method was used, and the weak absorption was 16.32ppm at 355nm and 1.91ppm at 1064nm. For the temperature rise test, under room temperature conditions, the film was irradiated with a 355nm picosecond ultrafast laser. After the laser stabilized, the partition was first opened, and a temperature gun was used to record the initial temperature of the test piece. Then, after a 1-minute interval, the temperature was measured and recorded. This was repeated after another 10-minute interval. The data was analyzed, and detailed data is shown in Table 5. The temperature rise test revealed a maximum difference of only 0.2℃, indicating virtually no temperature rise. It is generally considered that a temperature rise of less than 3℃ is excellent for high-power laser components. The film system solution provided in this example demonstrates significantly better temperature rise control than existing technologies.

[0056] Table 5. Test data on the damage resistance transmittance of the film deposited in Example 1.

[0057] 5. This embodiment provides a method for preparing a UV-resistant high-power antireflective film. By controlling the thickness ratio of the hafnium oxide layer, the film's ability to withstand UV-resistant high-power picosecond ultrafast lasers is improved. The film layer provided in Example 1 exhibits the following effects: 1. Strong resistance to wavelength drift (the wavelength range meeting the requirement of maximum reflectivity less than 0.25% reaches 22nm, far exceeding the 15nm required for normal mass production), high yield, and can meet the requirements for stable large-scale industrial production. 2. Strong resistance to damage testing, meeting the requirement of continuous irradiation by a picosecond pulsed laser for more than 15 days (approximately 360 hours), with transmittance >98% and no visible damage. 3. Low weak absorption; weak absorption at 355nm is <20ppm, and weak absorption at 1064nm is 1.91ppm. 4. Temperature rise at room temperature is only 0.2℃, far superior to the <3℃ of existing technologies.

[0058] Example 2 Further optimization based on Example 1 yielded the membrane system curve as shown below. Figure 11 , Figure 11 It can be seen that the wavelength range with reflectivity <0.25% is approximately 21~22nm. The corresponding film structure sequence is: hafnium oxide layer (4.445nm) → silicon oxide layer (188.64nm) → hafnium oxide layer (9.87nm) → silicon oxide layer (118.23nm) → hafnium oxide layer (12.27nm) → silicon oxide layer (77.805nm). The total thickness of the hafnium oxide layer is approximately 26.585nm, and the total film thickness is 411.26nm. The proportion of hafnium oxide layer thickness to the total thickness is 26.585 / 411.26, approximately 6.46%, which also meets all performance indicators and damage resistance tests.

[0059] As can be seen from the above embodiments, the preparation methods of Embodiments 1-2 of the present invention can be extended to other ultraviolet bands without changing the film material and the number of layers: the single-point target band is in the far ultraviolet to near ultraviolet range, i.e., 280~400nm. The hafnium oxide layer accounts for 6.46%~9.39% of the total film thickness, and it needs to meet optical specifications while ensuring strong resistance to wavelength shift and damage resistance of the film.

[0060] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. An antireflective film for the ultraviolet band, characterized in that, The ultraviolet antireflective coating has a film structure comprising a first hafnium oxide layer, a first silicon oxide layer, a second hafnium oxide layer, a second silicon oxide layer, a third hafnium oxide layer, and a third silicon oxide layer stacked sequentially, wherein the first hafnium oxide layer is in contact with the surface of the substrate; the total thickness of the first hafnium oxide layer, the second hafnium oxide layer, and the third hafnium oxide layer accounts for 5 to 10% of the total thickness of the film structure.

2. The ultraviolet antireflective film according to claim 1, characterized in that, The thickness of the first hafnium oxide layer is 4~8nm, the thickness of the first silicon oxide layer is 146~194nm, the thickness of the second hafnium oxide layer is 9~15nm, the thickness of the second silicon oxide layer is 97~121nm, the thickness of the third hafnium oxide layer is 11~13nm, and the thickness of the third silicon oxide layer is 75~81nm.

3. The ultraviolet antireflective film according to claim 1 or 2, characterized in that, The total thickness of the first hafnium oxide layer, the second hafnium oxide layer, and the third hafnium oxide layer is 32~36 nm; the total thickness of the film structure is 351~375 nm.

4. The ultraviolet antireflective film according to claim 3, characterized in that, The thickness of the first hafnium oxide layer is 7~8 nm, the thickness of the first silicon oxide layer is 146~155 nm, the thickness of the second hafnium oxide layer is 13~15 nm, the thickness of the second silicon oxide layer is 97~103 nm, the thickness of the third hafnium oxide layer is 12~13 nm, and the thickness of the third silicon oxide layer is 76~81 nm.

5. The ultraviolet antireflective film according to claim 1 or 2, characterized in that, The total thickness of the first hafnium oxide layer, the second hafnium oxide layer and the third hafnium oxide layer is 24~29 nm, and the total thickness of the film structure is 398~424 nm.

6. The ultraviolet antireflective film according to claim 5, characterized in that, The thickness of the first hafnium oxide layer is 4~5nm, the thickness of the first silicon oxide layer is 184~194nm, the thickness of the second hafnium oxide layer is 9~11nm, the thickness of the second silicon oxide layer is 115~121nm, the thickness of the third hafnium oxide layer is 11~13nm, and the thickness of the third silicon oxide layer is 75~80nm.

7. The method for preparing the ultraviolet antireflective film according to any one of claims 1 to 6, characterized in that, Includes the following steps: Based on the film material, optical band, and optical properties of the ultraviolet band antireflection film, film system design software is used to design the film system and obtain the film system design results of the ultraviolet band antireflection film. A first hafnium oxide layer, a first silicon oxide layer, a second hafnium oxide layer, a second silicon oxide layer, a third hafnium oxide layer, and a third silicon oxide layer are sequentially deposited on the surface of the substrate according to the film system design results to obtain the ultraviolet band antireflection film.

8. The preparation method according to claim 7, characterized in that, The deposition is performed using a vacuum evaporation deposition method; the deposition conditions include: initial vacuum degree ≤ 1.8E-3Pa; substrate heating temperature of 180~300℃; deposition rate of the first hafnium oxide layer, the second hafnium oxide layer and the third hafnium oxide layer of 0.1~0.25nm / s, and deposition rate of the first silicon oxide layer, the second silicon oxide layer and the third silicon oxide layer of 0.3~0.7nm / s.

9. An ultraviolet antireflection film element, characterized in that, It includes a substrate and an antireflection film disposed on both surfaces of the substrate; the antireflection film is the ultraviolet antireflection film according to any one of claims 1 to 6 or the ultraviolet antireflection film prepared by the preparation method according to claim 7 or 8.

10. The ultraviolet antireflection film element according to claim 9, characterized in that, The substrate is ultraviolet-fused silica glass; the substrate is cylindrical in shape, and the dimensions of the substrate are: diameter of 25.4 mm and thickness of 0.6~6 mm.

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