Low-thermal-effect laser film and preparation method thereof

Abstract

The application relates to the technical field of continuous laser optical film, in particular to a low-heat-effect laser film and a preparation method thereof. The method comprises the following steps: designing a film system according to laser wavelengths and optical performance and simulating and optimizing; precisely polishing a substrate, ultrasonic cleaning and activating; alternately preparing high and low refractive index functional layers and interface modification layers by physical vapor deposition and atomic layer deposition, setting the interface modification layers between the adjacent high and low refractive index functional layers, forming a periodic stacking structure; and annealing treatment under an inert atmosphere at 150-300 DEG C to obtain a finished product. The method has the advantages that: phonon bridging and interface passivation are realized through nano-Al2O3 interface modification, interface thermal resistance is significantly reduced, heat accumulation and thermal lens effect are inhibited, and the laser damage threshold is improved; the process is controllable, the film layer is dense and uniform, and the method is suitable for antireflection, high-reflection or light-splitting devices of high-power continuous laser systems.

Description

Technical Field

[0001] This invention relates to the field of continuous laser optical thin film technology, and in particular to a low-thermal-effect laser thin film and its preparation method. Background Technology

[0002] With the rapid development of high-energy continuous laser technology and the continuous improvement of laser system output power, extreme demands are placed on the performance of core optical components. As an indispensable core component in laser systems, the performance of optical thin films directly determines the output power limit, beam quality, and operational stability of the laser system.

[0003] Currently, the most widely used optical thin film in high-energy laser systems is the Ta2O5 / SiO2 alternating high and low refractive index film system. This system has advantages such as low optical loss, high refractive index matching, and stable mechanical properties, enabling excellent anti-reflection and high reflectivity optical properties. However, under high-energy continuous laser irradiation, this system faces a fatal technical bottleneck: the thermophysical properties of Ta2O5 and SiO2 are vastly different, resulting in extremely low overlap of phonon vibration spectra and severe phonon mismatch at the interfacial layer, leading to high interfacial thermal resistance. Under continuous laser irradiation, the laser energy absorbed by the film cannot be quickly conducted to the substrate for heat dissipation through the interface, resulting in severe steady-state heat accumulation within the film layer. This leads to thermal lensing, thermally induced wavefront distortion, thermal stress cracking, and even laser damage to the film layer, ultimately causing deterioration of laser beam quality, limited system output power, and even irreversible damage to optical components. Therefore, reducing the interfacial thermal resistance of the Ta2O5 / SiO2 film system and suppressing the thermal effects of continuous laser irradiation are core technical challenges in overcoming the performance limits of high-energy continuous laser systems.

[0004] To address the need for interface thermal resistance control and thermal effect suppression in high-energy continuous laser optical thin films, existing technologies generally suffer from the following shortcomings: Most existing solutions do not optimize for the root cause of Ta2O5 / SiO2 interface thermal resistance (i.e., phonon vibrational mode mismatch), making it difficult to fundamentally reduce interface thermal resistance. Traditional Ta2O5 / SiO2 interfaces exhibit low phonon spectral overlap and poor phonon interface transmittance. Interface thermal resistance is a major factor inducing thermal effect accumulation, and conventional methods such as doping, annealing, and substrate modification have limited effectiveness in improving this, resulting in insufficient suppression of continuous laser thermal effects. Furthermore, some existing solutions, while increasing film thermal conductivity through doping, introduce additional optical absorption and scattering losses, disrupting the film's optical interference effect and leading to reduced transmittance or reflectivity, making it difficult to meet the stringent optical performance requirements of high-energy laser systems. In addition, most optimization schemes are designed to improve the damage threshold of nanosecond and femtosecond pulsed lasers, focusing on defect passivation and anti-ionization damage optimization, without considering the characteristics of steady-state thermal accumulation in continuous lasers, resulting in poor applicability in continuous laser irradiation scenarios. Even with some similar interface control schemes, the interface layer is only used for defect passivation and environmental stability improvement. The interface material selection is not based on phonon spectrum matching, and atomic-level thickness precision control is not achieved. Therefore, an effective phonon bridging effect cannot be formed, and the interface thermal resistance control function is not available, making it difficult to effectively suppress the continuous laser thermal effect. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a low-thermal-effect laser thin film and its preparation method.

[0006] The primary objective of this invention is to provide a method for preparing a low-thermal-effect laser thin film, specifically comprising the following steps: S1. Based on the working wavelength and optical properties of the target laser, determine the thickness of the low refractive index functional layer, the interface modification layer, and the high refractive index functional layer, and optimize the film structure through optical simulation; the material of the low refractive index functional layer is SiO2, the material of the interface modification layer is Al2O3, and the material of the high refractive index functional layer is Ta2O5. S2. The substrate is subjected to ultra-precision polishing, multi-segment ultrasonic cleaning and plasma activation to make the surface roughness Ra≤0.5nm; S3. Under vacuum conditions, a first functional layer, an interface modification layer, a second functional layer, and an interface modification layer are sequentially prepared on the substrate to complete the preparation of one cycle of the base film unit; repeated deposition is used to form a base film unit with a stacking period of n; wherein, the two functional layers are a low refractive index functional layer and a high refractive index functional layer, respectively, which are prepared by physical vapor deposition; the interface modification layer is prepared by atomic layer deposition. S4. Annealing is performed in an inert atmosphere at 150~300℃ to complete the preparation of the thin film.

[0007] Preferably, the thickness of the interface modification layer is 0.5nm~10nm.

[0008] Preferably, the first functional layer, the interface modification layer and the second functional layer are SiO2, Al2O3 and Ta2O5, or Ta2O5, Al2O3 and SiO2, respectively. In step S3, physical vapor deposition includes electron beam evaporation, ion beam sputtering, and magnetron sputtering, with a deposition temperature of 150~300℃ and a deposition rate of 0.02~0.1nm / s; atomic layer deposition uses thermal atomic layer deposition or plasma-enhanced atomic layer deposition, with a deposition temperature of 80~300℃.

[0009] Preferably, the atomic layer deposition uses trimethylaluminum and high-purity water as precursors; the pulse sequence is trimethylaluminum pulse, inert gas purging, H2O pulse, and inert gas purging in sequence to form a cycle; the Al2O3 thickness deposited in each cycle is 0.1 nm.

[0010] Preferably, the stacking cycle in step S3 is 5 to 50.

[0011] Preferably, in step S2, the multi-segment ultrasonic cleaning includes: sequentially ultrasonically cleaning the substrate with acetone, anhydrous ethanol, deionized water, and petroleum ether, with each segment lasting 10-20 minutes; the surface activation includes: drying the substrate with high-purity nitrogen, sending it into the deposition chamber, and activating the substrate surface with argon / oxygen mixed plasma for 5-10 minutes.

[0012] Preferably, the substrate is fused silica, sapphire, monocrystalline silicon, or silicon carbide.

[0013] Preferably, the background vacuum degree in step S3 is ≤5×10 -4 Pa, the working gas for physical vapor deposition is a mixture of argon and oxygen.

[0014] The second objective of this invention is to provide a low-thermal-effect laser thin film, which is prepared using the aforementioned method for preparing a low-thermal-effect laser thin film.

[0015] Compared with the prior art, the present invention can achieve the following beneficial effects: Existing technologies have not optimized for phonon mismatch, the core source of interfacial thermal resistance. This invention directly solves the phonon mismatch problem between Ta2O5 and SiO2 through the phonon bridging effect of the nano-Al2O3 interfacial modification layer. It can significantly reduce the interfacial thermal resistance between films, open up the heat conduction channels inside the film, fundamentally solve the problem of film heat accumulation under continuous laser irradiation, and has a significant effect on suppressing the thermal effect of high-energy continuous laser, thus improving the performance limit of the laser system. This invention balances optical and heat dissipation performance without additional optical loss. Existing doping and modification methods, while optimizing thermal performance, introduce additional optical absorption and scattering losses, thus damaging the optical performance of the film system. This invention controls the thickness of the nano-Al2O3 interface modification layer to within 10nm and precisely compensates for the optical phase through film system design. The transmittance / reflectance of the film at the target wavelength is not significantly different from that of traditional film systems.

[0016] The film structure of this invention can be flexibly adapted to various optical thin films such as high-reflection films, anti-reflection films, beam splitters, and filters. It can be widely used in core optical components such as resonant cavity mirrors, output couplers, beam expanders, focusing mirrors, and galvanometers in various high-energy continuous laser systems such as continuous fiber lasers, solid-state lasers, and disk lasers. At the same time, it can be extended to laser optical components in the deep ultraviolet and mid-infrared bands, making it very widely applicable. Attached Figure Description

[0017] Figure 1 This is a flowchart of a method for preparing a low-thermal-effect laser thin film according to an embodiment of the present invention.

[0018] Figure 2 This is a schematic diagram of a low-thermal-effect laser thin film layer structure provided according to an embodiment of the present invention.

[0019] Figure 3 This is a transmittance test curve for a low-thermal-effect laser thin film provided according to an embodiment of the present invention.

[0020] Figure 4 This is a temperature rise test curve for a low-thermal-effect laser thin film provided according to an embodiment of the present invention.

[0021] Figure label: 1. Base; 2. Low-refractive-index functional layer; 3. Interface decoration layer; 4. High refractive index functional layer. Detailed Implementation

[0022] In the following description, embodiments of the invention will be described with reference to the accompanying drawings. In the description below, the same modules are denoted by the same reference numerals. Where the same reference numerals are used, their names and functions are also the same. Therefore, their detailed description will not be repeated.

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not constitute a limitation thereof.

[0024] This invention provides a method for preparing a low-thermal-effect laser thin film containing a nano-alumina interface modification layer, the flowchart of which is shown below. Figure 1 The preparation method specifically includes the following steps: S1. Film System Structure Design: Based on the target laser's operating wavelength and target optical properties (anti-reflection performance, high reflectivity, spectral dispersion, etc.), determine the physical thicknesses of the low-refractive-index functional layer, interface modification layer, and high-refractive-index functional layer. Optimize the film system using optical simulation software to compensate for the minor optical phase deviation introduced by the interface modification layer, ensuring that the film system meets the optical performance standards at the target wavelength without additional optical loss. The low-refractive-index functional layer is made of SiO2, the interface modification layer is made of Al2O3, and the high-refractive-index functional layer is made of Ta2O5.

[0025] S2. Optical substrate pretreatment: The optical substrate is subjected to ultra-precision polishing, multi-stage ultrasonic cleaning and surface activation to obtain a clean and highly active substrate surface; Specifically, optical materials such as fused silica, sapphire, single-crystal silicon or silicon carbide are selected as substrates, and the surface roughness Ra after pretreatment is ≤0.5nm; Ultra-precision polishing includes polishing the optical substrate to a surface roughness Ra≤0.5nm to ensure the flatness of the substrate surface and avoid introducing additional scattering loss; Multi-stage ultrasonic cleaning includes sequentially ultrasonically cleaning the substrate with acetone, anhydrous ethanol, deionized water, and petroleum ether, with each stage lasting 10-20 minutes, to remove oil and particulate impurities from the substrate surface. Surface activation includes: after cleaning, the substrate is dried with high-purity nitrogen and sent into the deposition chamber. The substrate surface is activated for 5-10 minutes using argon / oxygen mixed plasma to enhance the surface activity of the substrate and strengthen the adhesion between the film and the substrate.

[0026] S3. Composite Deposition Preparation: Physical vapor deposition (PVD) and atomic layer deposition (ALD) are alternately deposited in situ within the same vacuum chamber to achieve the insertion of an interface modification layer at each interface. The specific preparation process is as follows: S31. First functional layer deposition: The pretreated substrate is fixed in a vacuum chamber, and the vacuum level is evacuated to ≤5×10⁻⁶. -4 Pa; SiO2 or Ta2O5 is deposited on the substrate using physical vapor deposition (PVD) to obtain the first functional layer; that is, the first functional layer is a low refractive index functional layer or a high refractive index functional layer; Physical vapor deposition includes electron beam evaporation, ion beam sputtering, magnetron sputtering, etc.; the working gas is a mixture of argon and oxygen, the deposition temperature is controlled at 150~300℃, and the deposition rate is 0.02~0.1nm / s to ensure the density and uniformity of the film. S32. In-situ growth of interface modification layer by atomic layer deposition (ALD): Maintaining the vacuum level in the vacuum chamber, using thermal atomic layer deposition or plasma-enhanced atomic layer deposition process, with trimethylaluminum (TMA) and high-purity water as precursors; The deposition temperature is controlled at 80~300℃, and the pulse sequence is as follows: TMA pulse (0.05~0.2s), inert gas purging, H2O pulse (0.05~0.2s), inert gas purging, forming one deposition cycle; the number of cycles is set according to the target thickness, such as 1~20 cycles, corresponding to an Al2O3 layer thickness of 0.5~10nm; After growth, a uniform and dense nano-Al2O3 interface modification layer is obtained, which covers the surface of the first functional layer to avoid introducing additional optical scattering loss. The thickness of the interface modification layer is 0.5nm~10nm, preferably 1nm~5nm; in a specific embodiment, the thickness of each cycle deposition is 0.1nm; S33. Deposition of the second functional layer: Physical vapor deposition is used to deposit the second functional layer on the interface modification layer; the second functional layer and the first functional layer are functional layers with alternating refractive indices, that is, when the first functional layer is a low refractive index functional layer, the second functional layer is a high refractive index functional layer, and vice versa; the deposition process parameters are consistent with S31, the deposition temperature is controlled at 150℃~300℃, the deposition rate is 0.02~0.1nm / s, and the working gas is an Ar2 / O2 mixed gas to ensure the density and uniformity of the second functional layer; S34. Following the conditions in step S32, an interface modification layer is grown in situ on the second functional layer using atomic layer deposition; this completes the preparation of one cycle of the base film unit. S35. Repeat steps S31 to S34 to form a base film unit with a stacking period of n; where n = 5 to 50.

[0027] S4. Post-treatment after interface optimization: The deposited film is subjected to low-temperature annealing to optimize the interface bonding state and phonon transport channels, thereby achieving precise control of the inter-film interface thermal resistance. The specific operation is as follows: Annealing atmosphere: High-purity nitrogen or argon inert atmosphere to avoid high-temperature oxidation of the film; Annealing temperature: 150~300℃, to avoid high-temperature annealing causing grain scattering due to crystallization of Ta2O5 film; Annealing time: 1-4 hours, preferably 2 hours; After annealing, the furnace is naturally cooled to room temperature to eliminate interface defects, optimize the atomic bonding state of the interface, further improve the phonon interface transmittance, and reduce the interface thermal resistance.

[0028] The optical properties and thermal resistance to continuous laser irradiation of the prepared laser thin film were tested. The test indicators included: transmittance at the target wavelength, surface roughness of the film, and temperature rise of the film under continuous laser irradiation. The test results showed that: (1) the surface roughness Ra of the film was ≤5nm. (2) the transmittance of the film at the target wavelength was 99.9%, as shown in the attached figure. Figure 3 As shown. (3) The temperature rise of the sample was tested under 1064nm continuous laser conditions. The initial temperature of the sample was the same as the room temperature, which was 22℃. As the irradiation time increased, the temperature gradually rose. After irradiation for 180s, the temperature of the two samples tended to stabilize. At this time, the heat generated by the laser irradiation was consistent with the heat lost by the sample, and thermal equilibrium was reached. The temperature rise of the sample with the interface modification layer was about 2℃, and the temperature rise of the sample without the interface modification layer was about 2.7℃. The thermal effect was reduced by 35%, as shown in the attached figure. Figure 4 As shown. After passing the inspection, the film is encapsulated and protected in a clean environment to obtain a low-thermal-effect laser thin film product containing a nano-alumina interface modification layer.

[0029] The first functional layer, the interface modification layer, and the second functional layer of the present invention are SiO2, Al2O3, and Ta2O5, or Ta2O5, Al2O3, and SiO2, respectively. That is, the stacking order of the first functional layer and the second functional layer can be interchanged. Regardless of which layer is closer to the substrate, a nano-Al2O3 interface modification layer is inserted between adjacent functional layers to achieve full interface thermal resistance control.

[0030] In a specific embodiment, the structure of the laser thin film is as follows: Figure 2 As shown, it includes: an optical substrate 1, a low-refractive-index functional layer 2, an interface modification layer 3, and a high-refractive-index functional layer 4; the material of the low-refractive-index functional layer 2 is SiO2, the material of the interface modification layer 3 is Al2O3, and the material of the high-refractive-index functional layer 4 is Ta2O5; the interface modification layer 3 is disposed between each low-refractive-index functional layer and each high-refractive-index functional layer, forming an alternating stacked structure of "SiO2 / Al2O3 / Ta2O5 / Al2O3 / SiO2..." to achieve full interface thermal resistance control.

[0031] The core mechanism of this invention is the phonon bridging effect of the nano-Al2O3 interface modification layer, specifically as follows: The core source of interfacial thermal resistance is the mismatch of phonon vibration modes between the two materials. Phonons undergo strong inelastic scattering at the interface, failing to effectively transfer heat across the interface, which is the core bottleneck of thin film thermal conduction. In the traditional Ta2O5 / SiO2 interface, the phonon spectrum overlap between the two materials is low, resulting in severe phonon mismatch and high interfacial thermal resistance. The amorphous nano-Al2O3 layer introduced in this invention forms a transition layer at the thin film interface, reducing phonon interfacial scattering and thus significantly reducing interfacial thermal resistance. Simultaneously, the nano-Al2O3 interface modification layer prepared by ALD has atomic-level flatness, which can effectively passivate the defect states of the Ta2O5 / SiO2 interface, reduce laser absorption at the interface, further reduce thin film heat accumulation, and fundamentally suppress the thermal effects under continuous laser irradiation.

[0032] It should be understood that the various forms of processes shown above can be used to reorder, add, or delete steps. For example, the steps described in this invention disclosure can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution disclosed in this invention can be achieved, and this is not limited herein.

[0033] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for preparing a low-thermal-effect laser thin film, characterized in that: Specifically, the steps include the following: S1. Based on the working wavelength and optical properties of the target laser, determine the thickness of the low refractive index functional layer, the interface modification layer, and the high refractive index functional layer, and optimize the film structure through optical simulation; the material of the low refractive index functional layer is SiO2, the material of the interface modification layer is Al2O3, and the material of the high refractive index functional layer is Ta2O5. S2. The substrate is subjected to ultra-precision polishing, multi-segment ultrasonic cleaning and plasma activation to make the surface roughness Ra≤0.5nm; S3. Under vacuum conditions, a first functional layer, an interface modification layer, a second functional layer, and an interface modification layer are sequentially prepared on the substrate to complete the preparation of one cycle of the base film unit; repeated deposition is used to form a base film unit with a stacking period of n; wherein, the two functional layers are a low refractive index functional layer and a high refractive index functional layer, respectively, which are prepared by physical vapor deposition; the interface modification layer is prepared by atomic layer deposition. S4. Annealing is performed in an inert atmosphere at 150~300℃ to complete the preparation of the thin film.

2. The method for preparing a low-thermal-effect laser thin film according to claim 1, characterized in that: The thickness of the interface modification layer is 0.5nm~10nm.

3. The method for preparing a low-thermal-effect laser thin film according to claim 1, characterized in that: The first functional layer, the interface modification layer, and the second functional layer are SiO2, Al2O3, and Ta2O5, respectively, or Ta2O5, Al2O3, and SiO2, respectively. In step S3, physical vapor deposition includes electron beam evaporation, ion beam sputtering, and magnetron sputtering, with a deposition temperature of 150~300℃ and a deposition rate of 0.02~0.1nm / s. Atomic layer deposition employs thermal atomic layer deposition or plasma-enhanced atomic layer deposition processes, with deposition temperatures ranging from 80 to 300°C.

4. The method for preparing a low-thermal-effect laser thin film according to claim 3, characterized in that: The atomic layer deposition uses trimethylaluminum and high-purity water as precursors; the pulse sequence is trimethylaluminum pulse, inert gas purging, H2O pulse, inert gas purging, forming a cycle; the Al2O3 thickness deposited in each cycle is 0.1 nm.

5. The method for preparing a low-thermal-effect laser thin film according to claim 1, characterized in that: The stacking cycle in step S3 is 5 to 50.

6. The method for preparing a low-thermal-effect laser thin film according to claim 1, characterized in that: In step S2, the multi-segment ultrasonic cleaning includes: sequentially ultrasonically cleaning the substrate with acetone, anhydrous ethanol, deionized water, and petroleum ether, with each segment lasting 10-20 minutes; the surface activation includes: drying the substrate with high-purity nitrogen, sending it into the deposition chamber, and activating the substrate surface with argon / oxygen mixed plasma for 5-10 minutes.

7. The method for preparing a low-thermal-effect laser thin film according to claim 1, characterized in that: The substrate is fused silica, sapphire, monocrystalline silicon, or silicon carbide.

8. The method for preparing a low-thermal-effect laser thin film according to claim 1, characterized in that: In step S3, the background vacuum degree is ≤5×10⁻⁶. -4 Pa, the working gas for physical vapor deposition is a mixture of argon and oxygen.

9. A low-thermal-effect laser thin film, characterized in that: The laser thin film with low thermal effect is prepared using the method described in claim 1.

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