CN114590771A - A kind of micro-nano structure laser window and preparation method thereof - Google Patents

Abstract

The invention discloses a preparation method of a micro-nano-structured laser window with high transmittance and high-threshold anti-laser damage performance. The pump carries out the self-assembly of polystyrene microspheres and transfers them to the quartz glass after ultrasonic cleaning; (3) Reactive ion etching technology is used to etch the quartz substrate with polystyrene microspheres, and the quartz substrate is Prepare the micro-nano structure; (4) use chemical reagents to clean the quartz substrate to remove the incompletely reacted polystyrene microspheres; (5) test the transmittance of the laser window of the prepared quartz micro-nano structure, and use a strong laser Its performance was tested by radiation, which proved the successful preparation of a micro-nano-structured laser window with high transmittance and high-threshold anti-laser damage. The laser window of the micro-nano structure prepared by the method has high transmittance, wide anti-reflection band, strong anti-laser damage performance, and the method is simple.

Description

A kind of micro-nano structure laser window and preparation method thereof

technical field

The invention relates to a preparation method of a subwavelength scale micro-nano structure laser window with high transmittance and high threshold laser damage resistance, and belongs to the technical field of micro-nano processing.

Background technique

The development of high-power laser drivers and the research on laser inertial confinement fusion have been important hotspots in the field of high-power lasers since the 1970s, which can reflect the country's major needs. Countries around the world have carried out research on high-energy laser systems. Lasers in the near-infrared band have important uses and broad application prospects in scientific research and teaching, laser medical treatment, industrial processing, military aerospace and other fields. Laser anti-reflection window is one of the essential components in the laser system. Due to the high energy density of the laser beam in the high-power laser system, the surface damage of the laser anti-reflection window often occurs under strong laser irradiation, and the laser damage will reduce the transmittance to a certain extent; once the surface damage of the laser anti-reflection window occurs , which will affect the surface quality, and the laser irradiation on the damaged point will cause uneven light intensity distribution in the damaged area, thereby damaging the laser element again. The damage of laser components under strong laser irradiation seriously affects their service life, and is currently a major factor that inhibits the long-term safe and stable operation of high-power laser systems.

The current laser anti-reflection windows are mainly based on thin-film interference theory. However, the laser damage threshold of thin-film components is much lower than that of bare substrates. With the further development of high-power laser technology, the damage resistance of optical components and the environment Tolerance sets higher and higher requirements, which are increasingly difficult to meet with thin-film components. Based on this, the present invention proposes an antireflection laser window with a micro-nano structure. Micro-nano structure anti-reflection window refers to the preparation of micro-nano structures far smaller than the wavelength of the laser on the surface of the substrate material by etching and other methods. According to the equivalent medium theory, by adjusting the duty ratio of the microstructure, the effective refractive index of the film can be adjusted to satisfy the matching of the refractive index, thereby reducing the surface reflectivity and enhancing the transmission effect of the window. Since the micro-nano structure window is prepared by etching the material of the substrate itself, without introducing other materials, this single material system can provide a threshold of anti-laser damage similar to bulk materials on the one hand, effectively improve the anti-damage performance of the laser window, and on the other hand On the one hand, the thermal mismatch between the film material and the substrate caused by strong light radiation can be effectively avoided, and its stability can be improved.

Summary of the invention: Based on this, we propose to use colloidal sphere self-assembly technology combined with reactive ion etching technology to prepare micro-nano structures on a quartz substrate as a laser window. The laser window has high transmittance, wide antireflection band, and large antireflection angle range At the same time, this method is simple in operation, low in cost, can be fabricated in a large area, and can meet the development needs of large-diameter strong lasers.

The preparation method of a micro-nano structure laser window with high transmittance and high threshold laser damage resistance provided by the present invention, the specific steps are as follows:

1. Ultrasonic cleaning of the quartz glass substrate;

2. Using colloidal sphere self-assembly technology to prepare polystyrene monolayer film mask;

3. Using reactive ion etching technology to etch the quartz substrate;

4. Use organic solvent to remove incompletely reacted polystyrene microspheres;

5. The structure, morphology and performance characterization of the micro-nano-structured laser window.

In the above method, the cleaning of the quartz glass substrate mentioned in step 1 includes the following steps;

The quartz glass substrate is immersed in acetone, chloroform, ethanol, and deionized water for ultrasonic cleaning successively, with a power of 40-60w and a time of 3-10min. The polarities of the three chemical reagents are from small to large, which can fully remove the contamination on the surface of the quartz glass substrate. The cleaned quartz glass substrate is immersed in deionized water and is ready to use.

In step 2, the polystyrene monolayer film mask is prepared by using the colloidal ball self-assembly technology, and the specific steps are as follows:

(1) Prepare a water-ethanol mixture of monodispersed polystyrene microspheres with a particle size of 300nm-3000nm with a concentration of 1%-20% and a volume ratio of 1:1-1:5, and then place it in Ultrasound is carried out in an ultrasonic cleaner with a power of 40-100w, and the time is 10-60min, so that the mixture is evenly mixed;

(2) Add deionized water to the glass petri dish, immerse the quartz substrate in it, and use a micro-syringe pump to extract the sonicated monodisperse polystyrene microsphere mixture with a volume of 100uL-2mL, and inject it into the On the surface of deionized water in the glass petri dish, control the injection rate to be 0.1-2mL/h until the entire liquid surface is covered with polystyrene microspheres;

(3) The deionized water in the glass petri dish is slowly led out by using a U-shaped tube, and the polystyrene monolayer film is lowered as the liquid level drops until it falls to the surface of the quartz substrate. The quartz substrate is taken out and dried at room temperature. stand-by.

In step 3, reactive ion etching technology is used to etch the quartz substrate, and the specific steps are as follows: put the quartz substrate with the polystyrene microsphere monolayer film into the cavity of the reactive ion etching machine, evacuate, and set reaction conditions. The etching gas is oxygen (O ₂ ) and trifluoromethane (CHF ₃ ) gas, the gas flow is O ₂ : 5-50sccm, CHF ₃ : 20-50sccm, the etching radio frequency power (RF) is 30-200w, inductive coupling The power (ICP) is 0-100w, the cavity pressure (P) is 10-30mtorr, and the etching time is 10-100min. After the etching, the vacuum was broken, and the quartz substrate was taken out.

In step 4, use organic solvent to remove incompletely reacted polystyrene microspheres, and the specific steps are as follows:

The quartz substrate after reactive ion etching is immersed in tetrahydrofuran, anhydrous ethanol, and deionized water in turn, and ultrasonically cleaned, the ultrasonic power is 40-200w, and the ultrasonic time is 5-10min. Its blow dry.

The structure, morphology and performance characterization of the micro-nano-structured laser window in step 5, the specific steps are as follows:

Scanning tunneling electron microscopy was used to characterize the morphology of the microstructured laser window, measure its transmittance, and irradiate it with a high-power laser to test its anti-laser damage performance.

Compared with the existing laser window, the micro-nano structure laser window prepared by the present invention has the following advantages:

(1) The micro-nano-structured laser window prepared by this method has strong resistance to laser damage. Since the micro-structured window is prepared by etching the material of the substrate itself, no other materials are introduced. On the one hand, this single material system can provide similar substrate materials. The intrinsic laser damage resistance threshold can effectively improve the damage resistance of the laser window. On the other hand, it can effectively avoid the thermal mismatch between the film material and the substrate caused by strong light radiation, and improve its stability. The anti-laser damage threshold of the micro-nano-structured laser window can be close to the intrinsic threshold of the base material.

(2) The micro-nano-structured laser window prepared by this method has a wide antireflection band, a large antireflection angle and adjustable transmission properties.

(3) The method is low in cost, simple in operation, can be prepared in a large area, and can meet the development needs of large-diameter strong lasers.

Description of drawings

Fig. 1 is the preparation flow chart of the micro-nano structure quartz laser window according to the present invention, wherein a figure is a schematic diagram of self-assembly of polystyrene microspheres, b figure is a schematic diagram of reactive ion etching quartz substrate, (1) is deionization Water level, (2) Micro injector, (3) Polystyrene microspheres (4) Oxygen plasma, (5) Trifluoromethane plasma, (6) Quartz micro-nano structure.

In Figure 2, a is the actual process of the self-assembly of polystyrene microspheres, and b is the planar SEM image of the PS microsphere monolayer film with a diameter of 600 nm.

FIG. 3 is a cross-sectional SEM image of a micro-nano structure on a quartz substrate.

Figure a in Figure 4 shows the actual transmittance and the calculated residual reflectance of the blank substrate and the quartz substrate with micro-nano structure on one side. Figure b shows the transmittance of the quartz substrate with micro-nano structure on one side at different angles.

FIG. 5 is a graph showing the relationship between the surface temperature and the laser power density of the radiation of the micro-nano structure laser window under the laser radiation of 1030 nm wavelength.

Detailed ways

In order to make the objects and advantages of the present invention more clear, the present invention will be further described in detail below with reference to specific embodiments. It should be noted that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention. The invention mainly uses the colloidal ball etching technology and the reactive ion etching technology to prepare the laser window of the micro-nano structure. Large-area preparation can meet the development needs of large-diameter strong lasers.

Example 1:

As shown in Figure 1-5;

Polystyrene microsphere monolayer film was prepared by colloidal sphere self-assembly technology. Prepare a water-ethanol solution of monodispersed polystyrene microspheres with a particle size of 600nm and a concentration of 10% in a volume ratio of 1:1, and then place them in an ultrasonic cleaner with a power of 100w for 30min. , so that the solution is fully mixed.

Then, the ultrasonically cleaned quartz glass substrate was immersed in deionized water, and the ultrasonicated polystyrene microsphere monodisperse was extracted with a micro syringe and mounted on a micro syringe pump. The monodisperse of the spheres was injected into the deionized water surface at a constant speed, the injection speed was controlled to be 1mL/min, and the needle tip of the micro-injection pump was controlled to form a meniscus with the deionized water surface to reduce the verticality of the monodispersion of polystyrene microspheres. The direction of movement prevents the polystyrene microspheres from sinking into the water surface, until the deionized water surface is covered with polystyrene microspheres, and the injection is stopped;

Then, use a U-shaped tube to export the deionized water, fill the U-shaped tube with deionized water, insert one end into the glass petri dish, and connect the empty beaker at the other end, so that the liquid level in the glass petri dish is always higher than the liquid level in the beaker. The liquid level in the glass petri dish continued to drop, and the polystyrene microsphere monolayer film floating on the liquid surface also dropped. When the liquid level drops below the glass-quartz substrate, the polystyrene microsphere monolayer film is adsorbed on the glass-quartz substrate, the substrate is slowly taken out, and dried at room temperature to obtain the quartz with polystyrene microsphere-layered film. glass substrate. Using SEM to characterize the polystyrene microspheres on the quartz substrate, it can be seen that the polystyrene microspheres form a large-area ordered monolayer.

Quartz glass substrate with polystyrene microsphere tape layer film was etched by reactive ion etching technology.

The quartz substrate with polystyrene beads was etched by reactive ion etching.

The quartz substrate with polystyrene balls was loaded into a reactive ion etching machine, and after vacuuming, CHF ₃ and O ₂ gases were flushed. Under the glow discharge of the radio frequency power supply, the gases were ionized into plasma, which was mixed with polystyrene. The ethylene microspheres react with the quartz substrate, and finally micro-nano structures are etched on the surface of the quartz substrate. The gas flow is CHF ₃ : 50 sccm, O ₂ : 5 sccm, the RF power is 100w, the ICP power is 100w, the cavity pressure is 10mtorr, and the etching time is 20min. After the etching, the vacuum is broken, and the quartz substrate is taken out to obtain a quartz laser window with a micro-nano structure.

The structure, morphology and properties of the micro-nano-structured laser window were characterized. The etched quartz laser window of the micro-nano structure was cleaned with tetrahydrofuran to remove the incompletely reacted polystyrene microspheres, and the quartz micro-nano structure was characterized by SEM. The height of the micro-nano structure was about 550 nm and the width was about 600 nm. Next, the transmittance of the micro-nano structure quartz laser window was tested. In the range of 1000-1600nm, the transmittance of the quartz glass with micro-nano structure on one side is about 96%, and the transmittance at the wavelength of 1315nm is 96.2 %, the residual reflection is calculated to be about 0.4%. When measuring the transmittance of different incident angles, it can be seen that when the incident angle changes within 0°-40°, the transmittance at the wavelength of 1315nm has no significant change and remains above 96%. It shows that this microstructure window has a wide-angle antireflection effect. Then, the strong laser radiation experiment was carried out on the micro-nano-structured laser window to test its anti-laser damage performance. A continuous laser with a wavelength of 1030nm and a spot diameter of 3mm is used to irradiate the micro-nano structure laser window. The laser passing through the micro-nano structure laser window is used to receive and record the actual power with a power meter. The power gradually increases from 14.5w to 500w. The surface morphology of the micro-nano-structured laser window did not change. Use the convex lens to focus, reduce the diameter of the laser spot to 0.5mm, continue to irradiate the micro-nano-structured laser window, and use a thermal imager to record the temperature rise on the surface of the window. It can be seen that with the increase of power density, the temperature of the micro-structured window rises approximately Linear change, the power density increased by 1kw/cm2, the temperature increased by 0.1 ℃, indicating that the microstructure window has good resistance to strong laser radiation.

The micro-nano structure laser window prepared by this method has high transmittance, wide projection wavelength band, large transmission angle, strong anti-laser damage performance, and can realize large-area preparation, the transmittance band can be adjusted, and the performance is stable, which can meet the requirements of large-diameter and high-power The development needs of lasers.

Claims (10)

1. A method for preparing a micro-nano structure laser window is characterized by comprising the following steps:

(1) ultrasonically cleaning a quartz glass substrate, polishing the quartz glass, and then ultrasonically cleaning the quartz glass by sequentially using acetone, chloroform, absolute ethyl alcohol and deionized water;

(2) dispersing the polystyrene microspheres and transferring the polystyrene microspheres onto quartz glass after ultrasonic cleaning, and forming a single-layer film layer with the spread polystyrene microspheres on the upper surface of the quartz glass which is horizontally placed;

(3) etching the surface of a quartz substrate with polystyrene microspheres by using a reactive ion etching technology, and preparing a micro-nano structure on the quartz substrate;

(4) and cleaning the quartz substrate by using a chemical reagent to remove the incompletely reacted polystyrene microspheres.

2. The method of claim 1, wherein: the specific process of cleaning the quartz glass comprises the steps of ultrasonically cleaning the quartz glass by using acetone, chloroform, absolute ethyl alcohol and deionized water with the polarity from small to large in sequence, wherein the ultrasonic power is 40-60w, the cleaning time is 3-10min respectively, removing pollutants on the surface of the quartz glass, and immersing the cleaned quartz glass in the deionized water for later use.

3. The method of claim 1, wherein: the self-assembly process of the polystyrene microsphere comprises the following steps of (1) preparing a mixture of water and ethanol with the mass concentration of 1% -20% in a volume ratio of 1: 1-1: 5, placing the monodisperse solution of polystyrene microspheres with the particle size of 300nm-3000nm in an ultrasonic cleaner with the power of 40-100w for ultrasonic treatment for 10-60min to uniformly mix the mixed solution; (2) adding deionized water into a glass culture dish, immersing a quartz substrate in the deionized water, horizontally placing quartz glass, pumping a mixed solution of monodisperse polystyrene microspheres by using an injection pump, and injecting the mixed solution onto the surface of the deionized water in the glass culture dish at a constant speed, wherein the injection speed is controlled to be 0.1-2mL/h until the whole liquid surface is full of a layer of polystyrene microspheres; (3) and (3) leading out the deionized water in the glass culture dish, descending the polystyrene single-layer film along with the descending of the liquid level until the polystyrene single-layer film descends to the surface of the quartz substrate, taking out the quartz substrate to obtain the quartz glass substrate with the polystyrene microsphere single-layer film, and drying at room temperature for later use.

4. The method of claim 3, wherein: the deionized water in the glass culture dish is slowly led out by using a U-shaped pipe or a hose.

5. The method of claim 1, wherein: etching the quartz substrate with polystyrene microsphere by reactive ion etching, placing the quartz substrate with polystyrene microsphere single-layer film into a cavity of a reactive ion etching machine, vacuumizing, and setting reaction conditions, wherein the etching gas is oxygen (O)₂) And trifluoromethane (CHF)₃) Gas at a gas flow rate of O₂:5-50sccm，CHF₃20-50sccm, etching radio frequency power (RF) of 30-200w, Inductive Coupling Power (ICP) of 0-100w, cavity pressure (P) of 10-30mtorr, and etching time of 10-100 min; and after the operation is finished, deflating, and taking out the quartz substrate, wherein the surface of the quartz substrate forms a micro-nano structure.

6. The method of claim 1, wherein: removing the polystyrene microspheres remained on the surface of the quartz substrate after reactive ion etching by using an organic solvent, sequentially immersing the quartz substrate after reactive ion etching in tetrahydrofuran, absolute ethyl alcohol and deionized water, carrying out ultrasonic cleaning with the ultrasonic power of 40-200w and the ultrasonic time of 5-10min respectively, taking out the quartz substrate after ultrasonic cleaning is finished, and drying the quartz substrate by using nitrogen.

7. The method of claim 1, wherein: the performance of the micro-nano structure window is characterized; the method comprises the steps of utilizing a scanning tunnel electron microscope (SEM) to represent the appearance of a microstructure laser window, then measuring the transmittance of the microstructure laser window, utilizing high-power laser to radiate the microstructure laser window, and detecting the laser damage resistance of the microstructure laser window.

8. The method according to claim 1 or 7, characterized in that: and (3) carrying out transmittance test on the prepared quartz micro-nano structure laser window, and carrying out radiation detection on the quartz micro-nano structure laser window by using strong laser, thereby proving that the micro-nano structure laser window with high transmittance and high threshold value and capable of resisting laser damage is successfully prepared.

9. A laser window prepared according to the method of any one of claims 1 to 8.

10. The laser window according to claim 1 or 7, wherein: the laser window has high transmission high threshold laser damage resistance.

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