Processing method of CLBO crystal with high surface shape precision

Abstract

The invention discloses a processing method of a CLBO crystal with high surface shape precision, and belongs to the field of nonlinear optical crystals. The method comprises three procedures of cutting, heat treatment and polishing. The method comprises the following steps: firstly, cutting an oriented CLBO crystal under the cooling of cutting oil, then, carrying out heat treatment annealing on the cut crystal in an inert atmosphere, and finally, carrying out rough polishing, fine polishing and cleaning on the CLBO crystal subjected to heat treatment annealing to obtain the CLBO crystal with high surface shape precision. According to the processing method disclosed by the invention, the problems of deliquescence cracking and low processing surface shape precision in the processing of the CLBO crystal are effectively solved through a method for eliminating processing stress through heat treatment, inhibiting deliquescence by combining anhydrous polishing and water polishing and improving the polishing precision.

Description

Technical Field

[0001] This invention relates to the field of nonlinear optical crystal processing technology, and specifically to a processing method for a high-precision CLBO crystal. Background Technology

[0002] CLBO crystal (CsLiB6O10, i.e., lithium cesium borate) has excellent properties such as high nonlinear coefficient, high laser damage threshold and wide light transmission range. As the core material in the deep ultraviolet (193nm, 266nm) laser frequency conversion chain, it has irreplaceable application value in the fields of semiconductor lithography, precision micromachining, biomedical detection and ultraviolet radar.

[0003] The fabrication of high-optical-quality CLBO crystal devices for deep ultraviolet lasers faces two major challenges. First, eliminating defects such as microtubes, striations, and dislocations during crystal growth; second, ensuring high optical precision during device fabrication. The strong intrinsic hygroscopicity of CLBO crystals makes them prone to absorbing moisture from the air, leading to deliquescence and cracking. This poses a significant challenge to high-precision fabrication and is one of the main factors limiting their engineering applications. Currently, semi-bonded abrasive grinding and chemical mechanical polishing techniques, using anhydrous solvents and strictly controlling ambient temperature and humidity, have effectively suppressed the deliquescence and cracking problem of CLBO crystals during fabrication. However, issues such as low surface accuracy, poor stability, and susceptibility to cracking under operating conditions still exist.

[0004] Therefore, this invention discloses a method for processing a high-precision CLBO crystal. The method includes three steps: cutting, heat treatment, and polishing. First, the oriented CLBO crystal is cut to the required dimensions under non-aqueous cutting oil cooling. Then, the cut crystal is heat-treated and annealed in an inert atmosphere to eliminate cutting stress. Finally, the heat-treated and annealed CLBO crystal is subjected to anhydrous rough polishing, aqueous fine polishing, and anhydrous ultrasonic cleaning to obtain a high-precision CLBO crystal. This crystal can be used as a frequency doubling device for ultraviolet lasers. Summary of the Invention

[0005] This invention provides a method for processing CLBO crystals with high surface accuracy.

[0006] To achieve the above objectives, the present invention adopts the following technical solution.

[0007] A method for processing a high-precision CLBO crystal includes the following steps: First, the oriented CLBO crystal is cut to the required dimensions under cooling with non-aqueous cutting oil; then, the cut crystal is heat-treated and annealed in an inert atmosphere to eliminate cutting stress; finally, the heat-treated and annealed CLBO crystal is subjected to anhydrous rough polishing, aqueous fine polishing, and anhydrous ultrasonic cleaning to obtain a high-precision CLBO crystal.

[0008] Preferably, the heat treatment annealing temperature is 400-600℃, the holding time is 6-12h, and the cooling rate is ≤10℃ / h.

[0009] Preferably, the anhydrous coarse polishing is performed on an asphalt polishing pad using a non-aqueous polishing slurry containing SiC abrasive; the particle size of the SiC abrasive is 1-5μm, and the non-aqueous polishing slurry contains 10wt% SiC abrasive, 85wt% D80 environmentally friendly solvent oil, 3wt% Span 80 dispersant, and 2wt% organic amine.

[0010] Preferably, the water-based polishing is performed on a cloth disc using an aqueous polishing slurry containing cerium oxide abrasive; the cerium oxide abrasive has a particle size of 100 nm, and the aqueous polishing slurry contains 6 wt% cerium oxide abrasive, 90 wt% CLBO saturated aqueous solution, 1 wt% ammonium polyacrylate, and 3 wt% PEG800.

[0011] Preferably, the anhydrous ultrasonic cleaning is performed by ultrasonicating in acetone under an inert atmosphere for 3-5 minutes, followed by drying with high-purity nitrogen.

[0012] Preferably, the light-transmitting surface of the high-precision CLBO crystal has a surface precision of ≤λ / 10, and no cracks are generated when heated to 150℃.

[0013] The beneficial effects of this invention are as follows: To address the problems of low surface accuracy, poor stability, and susceptibility to cracking under operating conditions in CLBO crystal processing, this invention utilizes heat treatment annealing in an inert atmosphere to eliminate stress generated during cutting, suppressing crack nucleation and propagation caused by the coupling effect of surface processing stress and deliquescence. Furthermore, after significantly removing surface scratches and microcracks through anhydrous rough polishing, high surface accuracy is achieved by combining this with aqueous polishing. The aqueous polishing solution using saturated CLBO aqueous solution effectively suppresses short-term deliquescence of CLBO crystals, significantly improving surface accuracy. Attached Figure Description

[0014] Figure 1 This is a photograph of the actual CLBO crystal processed in Example 1.

[0015] Figure 2 This is a photograph of the actual CLBO crystal processed in Example 4. Detailed Implementation

[0016] To illustrate the present invention more clearly, the following embodiments are provided for illustrative purposes, but are not intended to limit the scope of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0017] The present invention will now be described in detail with reference to specific embodiments.

[0018] Example 1: Under non-aqueous cutting oil cooling, the oriented CLBO crystals were cut to dimensions of 10mm × 10mm × 15mm, with a machining allowance of 0.1mm. The cut blank was then heat-treated and annealed in a nitrogen atmosphere, heated to 400℃ at a rate of 10℃ / min and held for 12 hours, followed by cooling to room temperature at a rate of 5℃ / h. The annealed blank was then subjected to anhydrous rough polishing on an asphalt polishing pad, removing 70μm of material. The coarse-polished crystal was further subjected to aqueous fine polishing on a cloth disc, with a particle size of 1-5 μm, containing 10 wt% SiC abrasive with a particle size of 1-5 μm, 85 wt% D80 environmentally friendly solvent oil, 3 wt% Span 80 dispersant, and 2 wt% organic amine. The finely polished CLBO crystal was then subjected to aqueous fine polishing, with a particle size removal of 30 μm, using an aqueous polishing slurry containing 6 wt% cerium oxide abrasive with a particle size of 100 nm, 90 wt% CLBO saturated aqueous solution, 1 wt% ammonium polyacrylate, and 3 wt% PEG800. Finally, the finely polished CLBO crystal was ultrasonicated in acetone under a nitrogen atmosphere for 5 min, then removed and dried with high-purity nitrogen to obtain a CLBO crystal with high surface accuracy, as shown in the attached figure. Figure 1 As shown. The surface accuracy was measured to be λ / 12 using a laser interferometer; the CLBO crystal was heated to 150℃ in a nitrogen atmosphere, and no microcracks were generated on the surface.

[0019] Example 2: Under non-aqueous cutting oil cooling, the oriented CLBO crystals were cut to dimensions of 10mm × 10mm × 15mm, with a machining allowance of 0.1mm. The cut blank was then heat-treated and annealed in a nitrogen atmosphere, heated to 500℃ at a rate of 5℃ / min and held for 8 hours, followed by cooling to room temperature at a rate of 3℃ / h. The annealed blank was then subjected to anhydrous rough polishing on an asphalt polishing pad, removing 80μm of material. The polishing slurry contained 10 wt% SiC abrasive with a particle size of 1-5 μm, 85 wt% D80 environmentally friendly solvent oil, 3 wt% Span 80 dispersant, and 2 wt% organic amine. Further coarse polishing of the crystal involved aqueous fine polishing on a cloth disc, removing 20 μm particles. This aqueous polishing slurry contained 6 wt% cerium oxide abrasive with a particle size of 100 nm, 90 wt% CLBO saturated aqueous solution, 1 wt% ammonium polyacrylate, and 3 wt% PEG800. Finally, the finely polished CLBO crystal was ultrasonicated in acetone under a nitrogen atmosphere for 4 min, then removed and dried with high-purity nitrogen to obtain a CLBO crystal with high surface accuracy. Its surface accuracy was measured to be λ / 10 using a laser interferometer. Heating the processed CLBO crystal to 150℃ under a nitrogen atmosphere resulted in no microcracks on the surface.

[0020] Example 3: Under non-aqueous cutting oil cooling, the oriented CLBO crystals were cut to dimensions of 10mm × 10mm × 15mm, with a machining allowance of 0.1mm. The cut blank was then heat-treated and annealed in a nitrogen atmosphere, heated to 600℃ at a rate of 1℃ / min and held for 6 hours, followed by cooling to room temperature at a rate of 1℃ / h. The annealed blank was then subjected to anhydrous rough polishing on an asphalt polishing pad, removing 90μm of material. The polishing slurry contained 10 wt% SiC abrasive with a particle size of 1-5 μm, 85 wt% D80 environmentally friendly solvent oil, 3 wt% Span 80 dispersant, and 2 wt% organic amine. Further coarse polishing of the crystal involved aqueous fine polishing on a cloth disc to remove 10 μm particles. This aqueous polishing slurry contained 6 wt% cerium oxide abrasive with a particle size of 100 nm, 90 wt% CLBO saturated aqueous solution, 1 wt% ammonium polyacrylate, and 3 wt% PEG800. Finally, the finely polished CLBO crystal was ultrasonicated in acetone under a nitrogen atmosphere for 3 minutes, then removed and dried with high-purity nitrogen to obtain a CLBO crystal with high surface accuracy. Its surface accuracy was measured to be λ / 10 using a laser interferometer. Heating the processed CLBO crystal to 150℃ under a nitrogen atmosphere resulted in no microcracks on the surface.

[0021] Some embodiments The effects of heat treatment annealing temperature and cooling rate on the surface accuracy and crack formation of CLBO crystals were examined. The method and conditions were the same as in Example 1, except for the annealing temperature and cooling rate. The results are shown in the table below. Conclusion: Heat treatment temperatures as low as 300℃ cannot completely eliminate surface stress generated during processing. Even after heating to 150℃, a small number of microcracks still appear at the crystal edges, as shown in the attached image. Figure 2 As shown, when the annealing temperature is increased to 700℃, although no cracks are generated, the surface accuracy increases to λ / 6. When the cooling rate is increased to 15℃ / h, a small number of microcracks are also generated at the crystal edges. The results indicate that too low an annealing temperature and too high a cooling rate are both detrimental to stress relief during processing; while too high an annealing temperature leads to a decrease in surface accuracy.

[0022] Comparative Example 1 The difference between this comparative example and Example 1 is that the CLBO crystal was not subjected to heat treatment annealing after non-water cutting. The resulting CLBO crystal had a surface accuracy of λ / 10, but after heating to 150°C, numerous cracks appeared on the crystal surface and edges. Compared with Example 1, the results show that heat treatment annealing of the cut crystal is crucial to avoid crack formation.

[0023] Comparison Column 2 The difference between this comparative example and Example 1 is that the CLBO crystal underwent anhydrous rough polishing followed by anhydrous fine polishing. The polishing slurry used in this anhydrous fine polishing process contained 6 wt% cerium oxide abrasive with a particle size of 100 nm, 90 wt% D80 environmentally friendly solvent oil, 2 wt% Span 80 dispersant, and 2 wt% organic amine. The resulting CLBO crystal had a surface accuracy of λ / 8, but no cracks were generated after heating to 150°C. Compared with Example 1, the results show that using anhydrous rough polishing combined with aqueous fine polishing can effectively improve the surface accuracy of the processed crystal.

[0024] Comparison Column 3 The difference between this comparative example and Example 1 is that, in the aqueous polishing of the CLBO crystal, pure water was used instead of a saturated aqueous solution of CLBO in the aqueous polishing solution. The resulting CLBO crystal had a surface accuracy of λ / 12, but after heating to 150°C, numerous cracks appeared on the crystal surface and edges. Compared with Example 1, the results show that using a saturated aqueous solution of CLBO as the abrasive dispersion medium can effectively suppress deliquescence and avoid cracking during processing.

[0025] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A processing method of a high surface shape accuracy CLBO crystal, characterized in that, The processing method comprises the following steps: firstly, cutting the oriented CLBO crystal according to the required size under the cooling of non-aqueous cutting oil; then, performing heat treatment annealing on the cut crystal under an inert atmosphere to eliminate the cutting stress; finally, performing non-aqueous rough polishing, aqueous fine polishing and non-aqueous ultrasonic cleaning on the CLBO crystal after heat treatment annealing to obtain a high surface shape precision CLBO crystal.

2. The flux according to claim 1, wherein The heat treatment annealing temperature is 400-600 DEG C, the holding time is 6-12 h, and the cooling rate is ≤10 DEG C / h.

3. The flux according to claim 1, wherein The non-aqueous rough polishing is performed on a pitch polishing disc using non-aqueous polishing liquid containing SiC abrasive; the granularity of the SiC abrasive is 1-5 μm, and the non-aqueous polishing liquid comprises 10 wt% SiC abrasive, 85 wt% D80 environmentally-friendly solvent oil, 3 wt% Span 80 dispersant and 2 wt% organic amine.

4. The flux according to claim 1, wherein The aqueous fine polishing is performed on a flannelette disc using aqueous polishing liquid containing cerium oxide abrasive; the granularity of the cerium oxide abrasive is 100 nm, and the aqueous polishing liquid comprises 6 wt% cerium oxide abrasive, 90 wt% CLBO saturated aqueous solution, 1 wt% polyacrylamide and 3 wt% PEG 800.

5. The flux according to claim 1, wherein The non-aqueous ultrasonic cleaning is performed in acetone under an inert atmosphere for 3-5 min, and then the CLBO crystal is taken out and dried by blowing high-purity nitrogen.

6. The flux according to claim 1, wherein The high surface shape precision CLBO crystal has a surface shape precision of ≤λ / 10 on the light transmission surface, and no crack is generated when heated to 150 DEG C.

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