An additive manufacturing method for a laser window with a micro-nano structure and a laser window

Abstract

The present invention discloses an additive manufacturing method for a laser window with a micro-nano structure and a laser window. The steps include: 1) ultrasonically cleaning the polished quartz glass with a chemical reagent; (2) self-assembling polystyrene microspheres using a micro-injection pump and transferring them onto the ultrasonically cleaned quartz glass; (3) reducing the diameter of the polystyrene microspheres using an ion beam assisted coating technique and then coating a silica material thereon; (4) cleaning the quartz substrate with a chemical reagent to wash away the polystyrene microspheres with a part of silica; (5) performing secondary ion beam assisted coating on the cleaned quartz substrate. The laser window with a micro-nano structure prepared by this method has a high transmittance, a wide anti-reflection band, and strong laser damage resistance.

Description

Technical Field

[0001] The invention relates to a method for preparing a large-caliber micro-nano structure laser window with high transmittance, high threshold and anti-laser damage performance, belonging to the technical field of micro-nano processing. Background Art

[0002] With the rapid development of high-energy lasers, the demand for large-aperture optical components is increasing. For example, in the field of laser inertial confinement nuclear fusion, the National Ignition Facility (NIF) in the United States requires 7,360 large-aperture optical components with an aperture range of 0.5 to 1.0 m. As one of the key components in the laser, the damage caused by the laser window under strong laser irradiation is currently a major factor inhibiting the long-term safe and stable operation of high-power laser systems. Since the damage threshold of traditional dielectric film transmission components is difficult to improve, and with the further development of high-power laser technology, higher and higher requirements are put forward for the laser damage resistance and environmental tolerance of optical components, and thin film components are increasingly difficult to meet. In contrast, micro-nanostructure anti-reflection can achieve an anti-laser damage threshold close to the intrinsic material, so the micro-nanostructure laser window is expected to replace the traditional dielectric film transmission component. The micro-nanostructure anti-reflection window refers to a micro-nanostructure much smaller than the laser wavelength prepared on the surface of the substrate material. The laser cannot recognize the micro-nanostructure on the surface of this window, which can be approximated to be incident on a layer of thin film. According to the equivalent medium theory, by adjusting the duty cycle of the microstructure, the effective refractive index of the film can be adjusted to meet the refractive index matching, thereby reducing the surface reflectivity and enhancing the transmission effect of the window. Since the micro-nanostructure window and the substrate are made of the same material and no other materials are introduced, this single material system can provide a laser damage threshold close to that of the bulk material, effectively improving the damage resistance of the laser window, and on the other hand, it can effectively avoid the thermal mismatch between the film material and the substrate caused by strong light radiation, thereby improving its stability. There are many methods for preparing micro-nanostructures, which can be simply divided into subtractive manufacturing and additive manufacturing. Subtractive manufacturing refers to obtaining a microstructure by removing part of the substrate material through dry or wet etching. Wet etching is limited by the isotropy of etching and it is difficult to prepare microstructures with high aspect ratios, and the anti-reflection effect is poor. Dry etching, as a commonly used method for preparing microstructures, can be divided into purely physical ion beam etching and physical and chemical combined reactive ion etching. Ion beam etching uses high-energy rare gas ions to physically collide with the substrate material to etch the substrate material. It has poor selectivity for the substrate material, low etching efficiency, and a small microstructure aspect ratio, which is not conducive to the preparation of quartz microstructure windows. Reactive ion etching technology is mainly an etching method used in the field of chip manufacturing. It is difficult to ensure the uniformity of etching for large-aperture laser windows with a certain thickness, which limits the practical application of microstructure laser windows. Additive manufacturing methods can prepare large-aperture, uniform anti-reflection laser windows, but additive manufacturing methods represented by grazing angle deposition find it difficult to adjust the size and morphology of the microstructure.

[0003] Invention content: Based on this, we propose to use the additive manufacturing method of colloidal sphere self-assembly technology and ion beam assisted tilt angle deposition technology to prepare a micro-nano structure as a laser window on a quartz substrate. The laser window has the properties of high transmittance, wide anti-reflection band, and strong resistance to laser damage. At the same time, this method is simple to operate, low in cost, and can be prepared on a large area. It is expected to achieve the preparation of meter-level laser windows and meet the development needs of large-caliber strong lasers.

[0004] The present invention proposes a method for preparing a micro-nanostructure laser window with high transmittance, high threshold and anti-laser damage performance, and the specific steps are as follows:

[0005] 1. Ultrasonic cleaning of quartz glass substrate;

[0006] 2. Preparation of polystyrene monolayer mask using colloidal sphere self-assembly technology;

[0007] 3. Use ion source assisted coating technology to reduce the diameter of the polystyrene balls, and then coat them with a certain thickness of silicon dioxide layer;

[0008] 4. Using an organic solvent to remove the remaining polystyrene microspheres and the silicon oxide film deposited on their surface;

[0009] 5. Perform a second ion beam assisted tilt angle deposition of silicon oxide on the cleaned microstructure surface

[0010] 6. Structural morphology and performance characterization of micro-nanostructure laser windows.

[0011] In the above method, the cleaning of the quartz glass substrate mentioned in step 1 includes the following steps:

[0012] (1) Immerse the quartz glass substrate in acetone, chloroform, ethanol, and deionized water for ultrasonic cleaning in turn, with a power of 40-60w and a time of 3-10min. The polarity of the three chemical reagents increases from small to large, and the pollutants on the surface of the quartz glass substrate are fully removed. The cleaned quartz glass substrate is immersed in deionized water and set aside.

[0013] In step 2, a polystyrene monolayer mask is prepared by using colloidal sphere self-assembly technology, and the specific steps are as follows: (1) a water-ethanol mixture of monodispersed polystyrene microspheres with a particle size of 300nm-3000nm and a volume ratio of 1:1-1:5 with a concentration of 1%-20% is prepared, and then the mixture is placed in an ultrasonic cleaner with a power of 40-100W for ultrasonic cleaning for 10-60min to mix the mixture evenly;

[0014] (2) Deionized water is added to a glass culture dish, and the quartz substrate is immersed therein. A volume of 100 uL-2 mL of the mixed solution of monodisperse polystyrene microspheres after ultrasound is extracted by a microinjection pump, and the mixed solution is uniformly injected into the surface of the deionized water in the glass culture dish, and the injection speed is controlled to be 0.1-5 mL / h until the entire liquid surface is covered with polystyrene microspheres;

[0015] (3) Deionized water in the glass culture dish is slowly drained out using a U-shaped tube. The polystyrene monolayer film descends as the liquid level drops until it reaches the surface of the quartz substrate. The quartz substrate is taken out and dried at room temperature for later use.

[0016] In step 3, the diameter of the polystyrene balls is reduced by using ion source assisted coating technology, and a certain thickness of silicon dioxide layer is coated on them. The steps are as follows: the quartz substrate with a single layer of polystyrene microspheres is loaded into a fixture and placed in the chamber of an ion source assisted coating machine, vacuuming is performed, reaction conditions are set, the etching gas is oxygen (O2), the gas flow rate is set to 40-100sccm, the ion beam current is set to 600-1300mA, the beam voltage is 600-1300V, and the etching time is 10-60min during the etching process, which can effectively adjust the etching speed and morphology of the polystyrene balls. After etching, ion beam assisted coating is directly performed to deposit silicon dioxide material, and the deposition rate is controlled to be 0.1-1nm / s, the deposition temperature is 25-80°C, the deposition thickness is 100-500nm, and the beam current of the ion beam during the deposition process is 700-1300mA, the beam pressure is 700-1300V, and the oxygen flow rate is 40-100sccm, so that high-quality and low-absorption silicon oxide film can be obtained. After the silicon oxide deposition is completed, the vacuum is broken and the quartz substrate is taken out.

[0017] In step 4, an organic solvent is used to remove the remaining polystyrene microspheres and the silicon oxide film deposited on the surface thereof. The specific steps are as follows:

[0018] The quartz substrate after ion beam assisted tilt angle deposition was immersed in tetrahydrofuran, anhydrous ethanol, and deionized water in turn, and ultrasonically cleaned with an ultrasonic power of 40-200w and an ultrasonic time of 5-20min. After the ultrasonic cleaning, the quartz substrate was taken out and blown dry with nitrogen.

[0019] Step 5: Perform a second ion beam-assisted tilted angle deposition of silicon oxide on the cleaned microstructure surface. The specific steps are as follows: load the cleaned micro-nanostructure quartz substrate into a fixture and place it in the chamber of an ion source-assisted coating machine, evacuate the chamber, set the reaction conditions, use oxygen as the auxiliary gas, set the flow rate to 40-100 sccm, set the ion beam current to 700-1300 mA, and the beam pressure to 700-1300 V. Control the deposition rate to 0.1-1 nm / s, the deposition temperature to 25-80 ° C, and the deposition thickness to 20-500 nm. After the deposition is completed, break the vacuum and take out the sample.

[0020] The structural morphology and performance characterization of the micro-nanostructure laser window in step 6 are as follows:

[0021] The morphology of the microstructured laser window was characterized by a scanning tunneling electron microscope, its transmittance was measured, and it was irradiated with a high-power laser to detect its resistance to laser damage.

[0022] Compared with the existing laser windows, the micro-nanostructure laser window prepared by the present invention has the following advantages:

[0023] (1) The micro-nanostructure laser window prepared by this method has strong resistance to laser damage. Since the microstructure window and the substrate are made of the same material, silicon oxide, this single material system can effectively avoid the thermal mismatch between thin film materials of different materials and the substrate caused by strong light radiation, thereby improving its stability and anti-laser damage threshold.

[0024] (2) The micro-nanostructure laser window prepared by this method has a wide anti-reflection band, a large anti-reflection angle, and adjustable transmission properties.

[0025] (3) This method has low cost, simple operation, and can be prepared on a large scale. It is expected to realize the preparation of meter-level laser windows and meet the development needs of large-aperture high-intensity lasers. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Figure a is a planar SEM image of a PS ball monolayer film with a diameter of 500 nm, and figure b is a physical picture of a self-assembled PS ball monolayer film on the surface of a 300 mm diameter quartz substrate.

[0027] Figure 2 (a) The planar SEM image and cross-sectional SEM image of the polystyrene spheres after oxygen ion beam etching.

[0028] Figure 3 The planar SEM image (a) and cross-sectional SEM image (b) of the micro-nano structure after the first tilt angle deposition of silicon oxide and ultrasonic removal of polystyrene beads. The scale bars in the figures are 500nm.

[0029] Figure 4This is a planar SEM image of the microstructure finally prepared after two tilt-angle depositions, and the inset is its cross-sectional SEM image.

[0030] Figure 5 (a) is the transmittance spectrum of the micro-nano structure, and (b) is its weak absorption spectrum. DETAILED DESCRIPTION

[0031] In order to make the purpose and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments. It should be pointed out that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. The present invention mainly utilizes the colloidal sphere self-assembly technology combined with the ion beam assisted tilted angle plating deposition additive manufacturing method to prepare a micro-nano structure laser window. The laser window prepared by this method has high transmittance, a wide anti-reflection band, and strong resistance to laser damage. The method is simple and can be prepared on a large area. It is expected to achieve the preparation of meter-level laser windows and can meet the development needs of large-caliber strong lasers.

[0032] Embodiment 1:

[0033] 1) Ultrasonic cleaning of quartz glass substrate. Ultrasonic cleaning of quartz glass with a diameter of 300 mm and a thickness of 30 mm. The specific process is as follows: acetone, chloroform, anhydrous ethanol, and deionized water with increasing polarity are used to ultrasonically clean the quartz glass in sequence. The ultrasonic power is 60w, and the cleaning time is 5 minutes to remove pollutants on the surface of the quartz glass. The cleaned quartz glass is immersed in deionized water for standby use.

[0034] 2) Prepare a monolayer film of polystyrene microspheres using colloidal sphere self-assembly technology. Configure a water-ethanol solution with a volume ratio of 1:1 of monodisperse polystyrene microspheres with a particle size of 500 nm and a mass concentration of 10%. Then place it in an ultrasonic cleaner with a power of 100 W and ultrasonicate for 30 min to fully mix the solution evenly. Next, horizontally immerse the ultrasonically cleaned quartz glass substrate in deionized water. Use a micro syringe to extract 1 mL of the ultrasonically prepared monodisperse polystyrene microsphere solution and install it on a micro syringe pump. Use the micro syringe pump to uniformly inject the monodisperse polystyrene microsphere solution onto the surface of the deionized water, control the injection speed at 0.6 mL / min, and control the micro syringe pump needle tip to form a meniscus with the deionized water surface to reduce the vertical movement of the monodisperse polystyrene microsphere solution and prevent the polystyrene microspheres from sinking to the water surface until the deionized water surface is covered with polystyrene microspheres and stop injecting. The polystyrene microspheres gradually form a monolayer film from the edge of the container to the center of the container; then, use a U-shaped tube to drain the deionized water. Fill the U-shaped tube with deionized water, insert one end into the inside of a glass petri dish, and connect the other end to an empty beaker so that the liquid level in the glass petri dish is always higher than the liquid level in the beaker. According to the principle of the communicating vessel, the liquid level in the glass petri dish continuously drops, and the monolayer film of polystyrene microspheres floating on the liquid surface also drops accordingly. When the liquid level drops to the glass quartz substrate, the monolayer film of polystyrene microspheres adsorbs onto the glass quartz substrate. Slowly take out the substrate and dry it at room temperature to obtain a quartz glass substrate with a monolayer film of polystyrene microspheres. Characterize the polystyrene microspheres on the quartz substrate using SEM, and it can be seen that the polystyrene microspheres form a large-area ordered monolayer film, as shown in Figure 1 (a). Using this method, a large-area monolayer film can be formed on a 300 mm diameter quartz substrate, and the physical picture is as shown in Figure 1 (b).

[0035] 3) Use ion source assisted coating technology to reduce the diameter of the polystyrene microspheres and then deposit a certain thickness of silicon dioxide layer. Install the quartz substrate with a monolayer film of polystyrene microspheres in a fixture and place it in the cavity of an ion source assisted coating machine. Evacuate the air. O2 is used as the reaction gas and is ionized by the ion source to generate high-energy oxygen ions, which react with the polystyrene microspheres and the quartz substrate to etch the polystyrene microspheres. Set the gas flow rate to 60 sccm. During the etching process, set the ion beam current to 750 mA, the beam voltage to 750 V, and the etching time to 20 min. Control the etching temperature at about 50 °C, which can effectively adjust the etching morphology of the polystyrene microspheres. The morphology of the etched polystyrene microspheres is as shown in Figure 2As shown, the particle size of the etched polystyrene microspheres is about 70% of the original particle size. After the etching is completed, silicon dioxide material is directly deposited by ion beam-assisted coating. The deposition rate is controlled at 0.4 nm / s, the deposition temperature is 50 °C, the deposition thickness is 200 nm, and during the deposition process, the beam current of the ion beam is 900 mA, the beam voltage is 900 V, and the oxygen flow rate is 60 sccm to obtain a high-quality and low-absorption silicon oxide film. After the silicon dioxide deposition is completed, the vacuum is broken and the quartz substrate is taken out.

[0036] 4) Use organic solvents to remove the unreacted polystyrene microspheres completely. Immerse the quartz substrate deposited by ion beam-assisted tilting angle in tetrahydrofuran, absolute ethanol, and deionized water in sequence, and perform ultrasonic cleaning. The ultrasonic power is 100 w, and the ultrasonic time is 10 min. After the ultrasonic cleaning is completed, take out the quartz substrate and dry it with nitrogen. The plan view and cross-sectional view of the washed micro-nano structure are shown as Figure 3 shown.

[0037] 5) Perform the second ion beam-assisted tilting angle deposition of silicon dioxide on the surface of the washed micro-structure. A thin layer of quartz micro-structure has been formed on the surface of the washed quartz substrate, but due to its small size, it cannot meet the transmittance requirements, so the secondary ion source-assisted coating technology is required. Install the washed quartz substrate of the micro-nano structure in the fixture and place it in the cavity of the ion source-assisted coating machine. Evacuate the air, set the reaction conditions, the auxiliary gas is O2, the flow rate is set at 60 sccm, the beam current of the ion beam is 900 mA, the beam voltage is 900 V, and control the deposition rate at 0.4 nm / s and the deposition thickness at 150 nm. During the deposition process, the quartz substrate rotates at a constant speed, and the upper surface of the quartz substrate and the silicon dioxide deposition direction always maintain an angle of 75°, forming a structural shadow. Utilize the shadow shielding effect of the small-size micro-structure to deposit silicon dioxide in both the horizontal and vertical directions of the nano-pores. After the deposition is completed, break the vacuum and take out the sample. The plan view and cross-sectional SEM images of the micro-nano structure after the second tilting angle deposition are shown as Figure 4 shown. Compared with before the second deposition, the diameter of the nano-pores becomes smaller and the depth increases. Finally, a micro-nano pore array structure with a uniform period of 500 nm, a pore diameter of 300 nm, and a depth of 280 nm is formed on the surface of the quartz substrate.

[0038] 5) Characterize the properties of the micro-nano structure laser window. Test the transmittance of the quartz laser window with the micro-nano structure. In the wavelength range of 900 - 1800 nm, except for the absorption peak of JGS1 itself near the 1400 nm wavelength band, the transmittance of the quartz glass with a micro-nano structure on one side is greater than 95%. At a wavelength of 1315 nm, its transmittance is 96.0%, as shown in Figure 5 (a). This indicates that this micro-structure window has an anti-reflection effect in a wide wavelength band. Then, the weak absorption test of the micro-nano structure laser window was carried out, and the test results are shown in Figure 5(As shown in (b), the absorption of this microstructure at a wavelength of 1315 nm is less than 20 ppm, indicating that the components of our microstructure are single and the light absorption is weak, which helps to obtain a high laser damage threshold. Subsequently, a high-power laser radiation experiment was carried out on the micro-nano structured laser window to test its laser damage resistance performance. Using a continuous laser with a wavelength of 1030 nm and focusing it onto the sample surface with a convex lens, it was found that damage points began to appear on the sample surface only when the power density exceeded 100,000 watts per square centimeter, indicating that the microstructure window has good high-power laser radiation resistance performance.)

[0039] The micro-nano structured laser window prepared by this method has high transmittance, a wide projection band, strong laser damage resistance performance, and can be prepared on a large scale. It is expected to realize the preparation of a meter-level laser window. The transmittance band is adjustable, and the performance is stable, which can meet the development needs of large-aperture high-power lasers.)

Claims

1. An additive manufacturing method for a laser window with a micro-nano structure, characterized in that: (1) Ultrasonic cleaning of the quartz glass substrate: After the quartz glass is polished, it is successively ultrasonically cleaned with acetone, chloroform, absolute ethanol, and deionized water. (2) Polystyrene microspheres are dispersed in a solvent and transferred to the upper surface of the horizontally placed quartz glass after ultrasonic cleaning, forming a monolayer film layer with a flat paving of polystyrene microspheres on the upper surface of the horizontally placed quartz glass. (3) The diameter of the polystyrene microspheres is reduced by using an ion source-assisted coating technology, and then a silicon dioxide layer is deposited, and the deposition thickness of the silicon dioxide layer is 100 - 500 nm. (4) The quartz substrate is cleaned with a chemical reagent to wash away the polystyrene microspheres with part of the silicon dioxide. (5) The cleaned quartz substrate is subjected to secondary ion source-assisted deposition of silicon dioxide, and a certain thickness of silicon dioxide material is continuously deposited on the surface of the original structure to obtain the final structure, wherein the deposition thickness of the silicon dioxide material is 20 - 500 nm, and the angle between the silicon dioxide deposition direction and the surface of the quartz substrate is 60 - 85 degrees.

2. The method according to claim 1, wherein: Clean the quartz glass with a diameter of Ф10 - 300 mm and a thickness of 1 - 50 mm. The specific process is as follows: The quartz glass is successively ultrasonically cleaned with acetone, chloroform, absolute ethanol, and deionized water with increasing polarity. The ultrasonic power is 40 - 60 w, and the cleaning time is 3 - 10 min respectively, to remove the pollutants on the surface of the quartz glass. The cleaned quartz glass is immersed in deionized water for later use.

3. The method according to claim 1, wherein: The self-assembly process of polystyrene microspheres: (1) Prepare a monodisperse solution of polystyrene microspheres with a mass concentration of 1% - 20% and a particle size of 300 nm - 3000 nm. The solvent is a mixed solution of water and ethanol with a volume ratio of 1:1 - 1:

5. Then place it in an ultrasonic cleaner with a power of 40 - 100 w for ultrasonic treatment for 10 - 60 min to make the mixed solution evenly mixed; (2) Add deionized water to a glass petri dish and immerse the cleaned quartz substrate in it. The quartz glass is placed horizontally. Use a syringe pump to extract a mixed solution of 100 uL - 2 mL of ultrasonically treated monodisperse polystyrene microspheres and inject it evenly onto the surface of the deionized water in the glass petri dish at a controlled injection speed of 0.1 - 2 mL / h until the entire liquid surface is covered with a layer of polystyrene microspheres; (3) Drain the deionized water in the glass petri dish. The polystyrene monolayer film drops as the liquid level drops until it reaches the surface of the quartz substrate. Take out the quartz substrate to obtain a quartz glass substrate with a polystyrene microsphere monolayer film, and dry it at room temperature for later use.

4. The method according to claim 3, characterized in that: Use a U-shaped tube or a hose to drain the deionized water in the glass petri dish.

5. The method according to claim 1, wherein: The process of reducing the diameter of polystyrene microspheres and coating them with a silica layer using ion source-assisted coating technology is as follows: Place a quartz substrate with a monolayer film of polystyrene microspheres into the chamber of an ion source-assisted coating machine, evacuate the air, set the reaction conditions. The etching gas is oxygen (O2), the gas flow rate is 40 - 100 sccm, during the etching process, the ion beam current is 600 - 1300 mA, the beam voltage is 600 - 1300 V, and the etching time is 10 - 60 min; The etching temperature is controlled at 25 - 80 °C; after etching, the diameter of the polystyrene microspheres is 60 - 90% of the original diameter; After etching, directly carry out ion beam-assisted coating to deposit silica material. The deposition rate is 0.1 - 1 nm / s. During the deposition process, oxygen ion-assisted deposition is carried out. The oxygen flow rate is 40 - 100 sccm, the ion beam current is 700 - 1300 mA, the beam voltage is 700 - 1300 V, and the coating temperature is controlled at 25 - 80 °C; after the operation is completed, release the vacuum and take out the quartz substrate.

6. The method according to claim 1, wherein: Use an organic solvent to remove the polystyrene microspheres with a partial silica thin film. Immerse the coated quartz substrate successively in tetrahydrofuran, absolute ethanol, and deionized water, and perform ultrasonic cleaning. The ultrasonic power is 40 - 200 w, and the ultrasonic time is 5 - 20 min respectively. After ultrasonic cleaning is completed, take out the quartz substrate and dry it with nitrogen.

7. The method according to claim 1, characterized in that: Perform secondary ion source-assisted coating on the washed quartz substrate: The surface of the washed quartz substrate already has a thin layer of quartz microstructures, but due to their small size, they cannot meet the transmittance requirements, so secondary ion source-assisted coating technology is required; the coating conditions are as follows: the oxygen flow rate is 40 - 100 sccm, the ion beam current is 700 - 1300 A, the beam voltage is 700 - 1300 V, the deposition rate is 0.1 - 1 nm / s, and the deposition temperature is 25 - 80 °C; using the shadow masking effect of small-sized microstructures, the silica microstructures formed by secondary coating increase in size in both the vertical and horizontal directions; after coating is completed, break the vacuum and take out the quartz substrate.

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