阅读说明：本技术 一种易潮解kdp功能晶体局部凹凸表面的等材修平方法 (Equal material flattening method for local concave-convex surface of deliquescent KDP functional crystal ) 是由 程健 程旭盟 彭恩鸿 王景贺 陈明君 赵林杰 杨浩 刘启 谭超 武文强 于 2020-11-13 设计创作，主要内容包括：一种易潮解KDP功能晶体局部凹凸表面的等材修平方法,属于工程光学领域,用以解决由于现有表面微机械处理方法的局限性而导致的不能实现KDP功能晶体局部凹凸表面的平整化处理的问题。该方法的技术要点在于基于KDP晶体材料的易潮解特性,不增加或减少晶体材料,通过控制晶体元件加工环境的湿度,使晶体处于高湿度环境下,在微探针与KDP晶体表面形成水半月板,利用水溶剂的介入作用,对晶体表面局部凹凸形貌进行等材修平以实现晶体元件表面局部凹凸形貌的平整化处理。本发明可用于提升光学元件的激光损伤阈值和使用寿命。(A method for flattening equal materials of a KDP functional crystal local concave-convex surface easy to deliquesce belongs to the field of engineering optics and is used for solving the problem that flattening treatment of the KDP functional crystal local concave-convex surface cannot be achieved due to the limitation of the existing surface micro-mechanical treatment method. The method has the technical key points that based on the deliquescence characteristic of the KDP crystal material, the crystal material is not increased or reduced, the crystal is in a high-humidity environment by controlling the humidity of the processing environment of the crystal element, a water meniscus is formed on the surfaces of the microprobe and the KDP crystal, and the intervention effect of a water solvent is utilized to perform equal material leveling on the local concave-convex morphology of the crystal surface so as to realize the leveling treatment of the local concave-convex morphology of the crystal element surface. The invention can be used for improving the laser damage threshold and prolonging the service life of the optical element.)

1. A method for leveling equal materials on the local concave-convex surface of a KDP functional crystal easy to deliquesce is characterized by comprising the following steps,

the method comprises the following steps of firstly, utilizing a super-depth-of-field microscope and an atomic force microscope to perform off-line analysis and statistics on the surface morphology of the KDP crystal, and determining the position information and the characteristic size information of the local concave-convex surface to be flattened of the KDP functional crystal; wherein, the atomic force microscope is provided with a microprobe;

secondly, positioning the local concave-convex surface to be flattened of the KDP functional crystal by using a CCD (charge coupled device) camera according to the position information and the characteristic dimension information, and determining the relative position of the atomic force microscope microprobe and the local concave-convex surface to be flattened of the KDP functional crystal;

thirdly, carrying out online scanning and measurement on the concave-convex surface to be flattened of the part of the KDP functional crystal by using an atomic force microscope microprobe, and recording the initial concave-convex shape of the concave-convex surface to be flattened of the part of the KDP functional crystal;

setting corresponding relative humidity on the concave-convex surface to be flattened of the part of the KDP functional crystal in the step three by using an ultrasonic humidity adjusting device, and flattening the concave-convex surface to be flattened of the part of the KDP functional crystal by moving and scanning through an atomic force microscope microprobe;

and fifthly, applying an atomic force microscope online imaging function, performing online imaging on the local concave-convex surface to be flattened of the KDP functional crystal at intervals of fixed period time, judging whether the local concave-convex surface to be flattened of the KDP functional crystal tends to be stable or not, and stopping flattening after the local concave-convex surface tends to be stable.

2. The method for trimming the local concave-convex surface of the deliquescent KDP functional crystal according to claim 1, further comprising a sixth step of recording the surface morphology of the KDP functional crystal after final trimming after trimming is finished, analyzing the trimming effect and evaluating the quality of the trimmed surface.

3. The method for isosmotic leveling of the locally concave-convex surface of the deliquescent KDP functional crystal according to claim 1, wherein the relative humidity in the fourth step is in the range of 40% -85%.

4. The method for isosmotic leveling of the locally concave-convex surface of the deliquescent KDP functional crystal according to claim 3, wherein the relative humidity in the fourth step is 75%.

5. The method for trimming the materials of the local concave-convex surface of the deliquescent KDP functional crystal according to claim 1, wherein the trimming principle in the fourth step is based on the deliquescent property of the material of the KDP functional crystal, and water meniscus is formed by adsorbing water molecules in the air under the action of capillary force between the microprobe and the surface of the KDP functional crystal in a high-humidity environment, so that the materials are transported and redistributed.

6. The method for isosmotic smoothing of the locally concave-convex surface of the deliquescent KDP functional crystal according to claim 1, wherein in the fifth step, the fixed period time is three minutes.

7. The method for trimming the deliquescent KDP functional crystal local concave-convex surface by using the equivalent material as claimed in claim 1, wherein the criterion for judging whether the local concave-convex surface to be trimmed of the KDP functional crystal tends to be stable in the fifth step is whether the curvature radius of the convex or concave part of the KDP functional crystal surface is larger than a preset value.

Technical Field

The invention relates to the field of engineering optics, in particular to a material-equivalent flattening method for a local concave-convex surface of a deliquescent KDP functional crystal.

Technical Field

The large-size KDP functional crystal is an important optical component in a high-power solid laser device, and is the only crystal material which can be used as a Pockels box and a frequency doubling converter at present. It is a typical soft and brittle material that is deliquescent, susceptible to cracking, sensitive to temperature changes, and one of the most difficult materials to process internationally recognized. Because the KDP crystal is soft and crisp, easy to crack and easy to deliquesce, the traditional processing methods such as grinding, polishing and the like cannot obtain high-quality and high-precision optical surfaces. At the present stage, single-point diamond fly-cutting machining is the most ideal ultra-precision machining method for large-caliber KDP crystals, but due to vibration of a main shaft, fluctuation of micro-feeding, size effect and plowing effect of materials during cutting and soft and brittle characteristics of crystal materials in the single-point diamond ultra-precision fly-cutting machining process, uneven morphological characteristics (such as micro-protrusions, micro-concave pits, micro scratches, micro cracks and the like) of local surfaces are inevitably introduced into the fly-cutting machining surface. When the KDP crystal after being processed and prepared is in service in a high-power solid laser system, the local concave-convex shape of the crystal surface introduced by processing can generate a strong modulation effect on incident laser, and particularly under the irradiation of frequency tripling ultraviolet strong laser, the local light intensity enhancement can induce a crystal element to generate further laser damage. The aggravation of the laser damage behavior on the surface of the crystal element can cause the reduction of the light transmission performance of the crystal element, and the energy flux density of strong laser output and the service life of the optical element are seriously influenced. If the local concave-convex morphology of the processing surface of the crystal element is not processed in time, the crystal element can be damaged and damage is increased under the irradiation of strong laser, so that the whole optical element is damaged, and the whole laser optical path system is finally influenced. Therefore, a method for quickly and effectively flattening the local concave-convex morphology of the surface of the KDP functional crystal is urgently needed.

Common optical surface treatment methods at present include methods such as CO2 laser ablation, chemical etching, ultrashort pulse machine tool ablation, micromechanical removal and the like. Because the KDP crystal material is soft and crisp, easy to deliquesce, easy to crack and the like, the micro-mechanical removal method based on material reduction processing is the most mainstream surface treatment method of the KDP crystal element. Although the method can remove the defect points on the crystal surface, thereby inhibiting the further expansion of the micro defect points on the crystal surface under the irradiation of strong laser, thereby improving the laser damage resistance of the crystal element and delaying the service life of the crystal element, the surface treatment method still has the following defects: 1. in the micromechanical processing method based on the material reduction processing, due to the size limitation of a used micro cutter, the local surface concave-convex morphology with the characteristic size smaller than 10 mu m cannot be processed, and the local surface concave-convex morphology with the characteristic size larger than 10 mu m needs to damage a large number of intact surfaces, and the processed curved surface contour is left on the processed surface, so that the 'flattening' cannot be realized in the true sense; 2. because the existing micro-mechanical processing method belongs to the field of material reduction processing, a large number of intact surfaces can be damaged in the processing process, so that the times of material reduction processing on the surfaces are limited, and the light transmission performance of the processed crystal element gradually becomes worse along with the increase of the times of processing; 3. because the micro-mechanical processing is based on the small tool head to process the crystal surface according to the set track, the residual knife-line appearance is inevitably left on the processed surface in the processing process, and the residual micro-knife-line also obviously influences the optical performance of the crystal element; 4. after the micro-machining based on the material reduction, a residual curved surface contour is left on the surface of the crystal element, and the contour structure can generate strong far-field modulation action on incident laser, so that a downstream far field of the crystal element generates an enhanced hot spot, and laser damage of a downstream optical element can be easily caused.

Disclosure of Invention

In view of the above problems, the invention provides a method for leveling an equivalent material of a local concave-convex surface of a KDP functional crystal, which is easy to deliquesce, and is used for solving the problem that the leveling treatment of the local concave-convex surface of the KDP functional crystal cannot be realized due to the limitation of the existing surface micro-mechanical treatment method.

A method for leveling iso-material of local concave-convex surface of KDP functional crystal easy to deliquesce comprises the following steps,

the method comprises the following steps of firstly, utilizing a super-depth-of-field microscope and an atomic force microscope to perform off-line analysis and statistics on the surface morphology of the KDP crystal, and determining the position information and the characteristic size information of the local concave-convex surface to be flattened of the KDP functional crystal; wherein, the atomic force microscope is provided with a microprobe;

secondly, positioning the local concave-convex surface to be flattened of the KDP functional crystal by using a CCD (charge coupled device) camera according to the position information and the characteristic dimension information, and determining the relative position of the atomic force microscope microprobe and the local concave-convex surface to be flattened of the KDP functional crystal;

thirdly, carrying out online scanning and measurement on the concave-convex surface to be flattened of the part of the KDP functional crystal by using an atomic force microscope microprobe, and recording the initial concave-convex shape of the concave-convex surface to be flattened of the part of the KDP functional crystal;

setting corresponding relative humidity on the concave-convex surface to be flattened of the part of the KDP functional crystal in the step three by using an ultrasonic humidity adjusting device, and flattening the concave-convex surface to be flattened of the part of the KDP functional crystal by moving and scanning through an atomic force microscope microprobe;

and fifthly, applying an atomic force microscope online imaging function, performing online imaging on the local concave-convex surface to be flattened of the KDP functional crystal at intervals of fixed period time, judging whether the local concave-convex surface to be flattened of the KDP functional crystal tends to be stable or not, and stopping flattening after the local concave-convex surface tends to be stable.

And further, recording the surface morphology of the KDP functional crystal after final leveling after the leveling is finished, analyzing the leveling effect and evaluating the quality of the leveled surface.

Further, the relative humidity in the fourth step is in the range of 40-85%.

Further, the relative humidity in step four was 75%.

Further, the leveling principle in the fourth step is based on the characteristic that a KDP functional crystal is easy to deliquesce, water molecules in air are adsorbed by the microprobe and the surface capillary force of the KDP functional crystal under the high humidity environment to form a water meniscus, substances are transported, and redistribution of the substances is achieved.

Further, in step five, the fixed cycle time is three minutes.

Further, the criterion for judging whether the local concave-convex surface to be flattened of the KDP functional crystal tends to be stable in the fifth step is whether the curvature radiuses of the convex or concave parts of the surface of the KDP functional crystal are both larger than a preset value.

The beneficial technical effects of the invention are as follows:

in consideration of the limitation of the existing surface micro-mechanical processing method of the KDP functional crystal, the invention provides a material leveling method of the local concave-convex surface of the KDP functional crystal based on the deliquescence characteristic of a KDP crystal material, namely, the leveling processing of the local concave-convex morphology of the surface of the crystal element is realized without increasing or reducing the crystal material. The method is characterized in that the humidity of the processing environment of a crystal element is controlled, so that the crystal is in a high-humidity environment, a water meniscus is formed on the surfaces of a microprobe and a KDP crystal, and the intervention effect of a water solvent is utilized to flatten the local concave-convex shape of the surface of the crystal by using equivalent materials. Compared with the common crystal surface treatment method, the method has the following advantages:

1. the intervention effect of the hydrosolvent can not limit the size of the processing area, so that the flattening treatment of the local micro concave-convex surface appearance with the characteristic dimension less than 10 mu m can be realized;

2. the existing intact crystal surface is not damaged, so that the flattening can be carried out for infinite times without reducing the light transmission performance of the crystal element;

3. the flattening recovery of the local concave-convex morphology on the surface of the crystal element can be realized, so that the damage and the damage of a downstream optical element caused by far-field modulation after the flattening can be avoided;

4. through the flattening treatment of the local concave-convex morphology of the crystal surface, the surface roughness of the flattened crystal element can be improved, and then the laser damage threshold value of the optical element is improved and the service life of the optical element is prolonged.

Drawings

The invention may be better understood by referring to the following description in conjunction with the accompanying drawings, in which like reference numerals are used throughout the figures to indicate like or similar parts. The accompanying drawings, which are incorporated in and form a part of this specification, illustrate preferred embodiments of the present invention and, together with the detailed description, serve to further explain the principles and advantages of the invention.

Fig. 1 shows a schematic flow chart of an iso-material flattening method for a local concave-convex surface of a deliquescent KDP functional crystal according to an embodiment of the invention.

Fig. 2 is a schematic diagram illustrating an initial concave-convex surface topography to be flattened in an equivalent material flattening method for a local concave-convex surface of a deliquescent KDP functional crystal according to an embodiment of the present invention.

Fig. 3 is a schematic diagram illustrating a flattening principle of an isogenous flattening method for a locally concave-convex surface of a deliquescent KDP functional crystal according to an embodiment of the present invention.

Fig. 4 shows a surface topography schematic diagram after the surface topography is flattened by the isogenous flattening method for the local concave-convex surface of the deliquescent KDP functional crystal according to the embodiment of the invention.

Fig. 5 shows a schematic diagram of an experimental apparatus for an iso-material flattening method of a local concave-convex surface of a deliquescent KDP functional crystal according to an embodiment of the present invention.

Detailed Description

Exemplary embodiments of the present invention will be described hereinafter with reference to the accompanying drawings. In the interest of clarity and conciseness, not all features of an actual implementation are described in the specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. It should be noted that, in order to avoid obscuring the present invention with unnecessary details, only the device structures and/or processing steps closely related to the solution according to the present invention are shown in the drawings, and other details not so relevant to the present invention are omitted.

In consideration of the limitation of the existing surface micro-mechanical processing method of the KDP functional crystal, the invention provides a material leveling method of the local concave-convex surface of the KDP functional crystal based on the deliquescence characteristic of a KDP crystal material, namely, the leveling processing of the local concave-convex morphology of the surface of the crystal element is realized without increasing or reducing the crystal material. The method is characterized in that the humidity of the processing environment of a crystal element is controlled, so that the crystal is in a high-humidity environment, a water meniscus is formed on the surfaces of a microprobe and a KDP crystal, and the intervention effect of a water solvent is utilized to flatten the local concave-convex shape of the surface of the crystal by using equivalent materials. Fig. 1 shows a schematic flow chart of an iso-material flattening method for a local concave-convex surface of a deliquescent KDP functional crystal according to an embodiment of the invention.

As shown in fig. 1, the method includes the steps of,

the method comprises the following steps of firstly, utilizing a super-depth-of-field microscope and an atomic force microscope to perform off-line analysis and statistics on the surface morphology of the KDP crystal, and determining the position information and the characteristic size information of the local concave-convex surface to be flattened of the KDP functional crystal; wherein, the atomic force microscope is provided with a microprobe.

According to the embodiment of the invention, firstly, an ultra-depth-of-field microscope (such as an ultra-depth-of-field optical microscope with the model of VHE-1000E, the maximum magnification of which is 5000 times) is adopted to observe the surface topography characteristics of a KDP crystal in a large range, the position distribution of the concave-convex topography of the surface is counted, and position information is provided for the positioning of a microprobe on an atomic force microscope; then, according to the position distribution observed by the ultra-depth-of-field microscope, observing and counting the characteristic size information of the local concave-convex morphology of the crystal surface by using an atomic force microscope (such as the atomic force microscope with the model number of Bruker Dimension Fastscan); and determining the area range to be flattened according to the statistical information, and recording the flattening quantity and the position information.

Secondly, positioning the local concave-convex surface to be flattened of the KDP functional crystal by using a CCD (charge coupled device) camera according to the position information and the characteristic dimension information, and determining the relative position of the atomic force microscope microprobe and the local concave-convex surface to be flattened of the KDP functional crystal;

thirdly, carrying out online scanning and measurement on the concave-convex surface to be flattened of the part of the KDP functional crystal by using an atomic force microscope microprobe, and recording the initial concave-convex shape of the concave-convex surface to be flattened of the part of the KDP functional crystal;

according to the embodiment of the invention, the concave-convex morphology of the initial surface to be flattened is measured and recorded by utilizing the on-line imaging function of the atomic force microscope, as shown in fig. 2, as can be seen from fig. 2, the two sides of the original surface are convex and the middle is concave before the KDP functional crystal is flattened, and the height of the concave-convex morphology is 71.7 nm.

Setting corresponding relative humidity on the concave-convex surface to be flattened of the part of the KDP functional crystal in the step three by using an ultrasonic humidity adjusting device, and flattening the concave-convex surface to be flattened of the part of the KDP functional crystal by moving and scanning through an atomic force microscope microprobe;

according to the embodiment of the invention, the ultrasonic humidity adjusting device is utilized to control the humidity according to the topography (the topography and the dimension) of the local to-be-flattened concave-convex surface of the crystal surface. Since the temperature also affects the formation of the water meniscus, the working environment is set to 20 ℃ at room temperature; and in order to facilitate the formation of water meniscus, the relative humidity is not less than 40%; to prevent deliquescence of the intact surface of the crystal, the relative humidity does not exceed 85%. Before the flattening experiment, the concave-convex shapes with different characteristic sizes are flattened in different humidity environments (the relative humidity is increased from 45% to 85%, and is increased by 10% every time), the final flattening result is recorded, the flattening effect under different humidities is compared, the appropriate relative humidity is determined to be 75%, and the flattening experiment is carried out.

The flattening experiment is based on the characteristic that KDP crystal material is easy to deliquesce, water meniscus is formed by adsorbing water molecules in the air through the capillary force action of the probe and the surface of the KDP crystal in a high humidity environment, the substance is transported, and redistribution of the substance is achieved. After the water meniscus is formed, the dissolved KDP crystal material quickly reaches saturation, and the crystal material is carried under the intervention action of the water solvent, so that the flattening effect of the local concave-convex morphology characteristics of the crystal surface is realized. Fig. 3 is a schematic diagram illustrating a flattening principle of an isogenous flattening method for a locally concave-convex surface of a deliquescent KDP functional crystal according to an embodiment of the present invention. As shown in fig. 3, at the local depression, KDP crystals are stacked on both sides to provide a substance for local depression to be leveled. With the reciprocating scanning movement of the microprobe, the surface of the crystal gradually evolves from the original appearance shown in 3 in fig. 3 to the appearance shown in 2, and with the progress of the flattening work, the surface appearance gradually evolves from the appearance shown in 2 to the appearance shown in 1 and finally tends to be stable. And for the surface convex appearance characteristics, both sides are provided with concave parts, so that a material storage space is provided for flattening the convex parts. With the reciprocating scanning movement of the microprobe, the surface of the crystal gradually evolves from the original appearance shown by 6 in fig. 3 to the appearance shown by 5, and with the progress of the flattening work, the surface appearance gradually evolves from the appearance shown by 5 to the appearance shown by 4 and finally tends to be stable.

Fifthly, applying an atomic force microscope online imaging function, performing online imaging on the local concave-convex surface to be flattened of the KDP functional crystal at intervals of a fixed period of time, judging whether the local concave-convex surface to be flattened of the KDP functional crystal tends to be stable or not, and stopping flattening after the local concave-convex surface tends to be stable;

according to the embodiment of the invention, the local concave-convex surface morphology of the crystal is flattened by using the microprobe, the surface morphology is scanned and imaged every three minutes by using the online imaging function of the atomic force microscope, and the flattening experiment is stopped after the surface morphology tends to be stable. Under the condition of 75% of relative humidity, after 87 minutes, the surface to be flattened of the crystal tends to be stable, as shown in fig. 3, when the surface appearance tends to be stable, namely the curvature radius of the convex or concave part of the surface is larger, the crystal does not move with the probe to redistribute, and the aqueous solvent does not have the material transportation capacity any more, so that the flattening effect of the local convex and concave appearance of the surface of the crystal is achieved.

And sixthly, recording the surface morphology of the KDP functional crystal after final leveling after the leveling is finished, analyzing the leveling effect and evaluating the quality of the leveled surface.

According to the embodiment of the invention, the obtained final surface is analyzed, the atomic force microscope is adopted to measure and observe the two-dimensional and three-dimensional shapes of the final surface, and whether the concave-convex shape of the surface to be repaired is restored to be flat or not and whether the surface roughness reaches the expected target or not is judged. Fig. 4 shows a surface topography schematic diagram after the surface topography is flattened by the isogenous flattening method for the local concave-convex surface of the deliquescent KDP functional crystal according to the embodiment of the invention.

As can be seen from FIG. 4, the surface of the crystal after the leveling tends to be flat, the height of the microscopic concave-convex morphology of the surface is reduced to 7.3nm, which is close to 90% relative to the height before the leveling, and the leveling effect is obvious. Through detection, the surface roughness Ra of the flattened area is reduced to 1.62nm from the initial 14.7nm, and the surface quality of the crystal after flattening is obviously improved.

Fig. 5 shows a schematic diagram of an experimental apparatus for an iso-material flattening method of a local concave-convex surface of a deliquescent KDP functional crystal according to an embodiment of the present invention.

Furthermore, the improvement of the surface quality of the crystal element can improve the laser damage threshold of the element, so that the water solvent intervention surface equal material flattening method based on the deliquescent property of the KDP crystal is a quick and effective KDP crystal surface treatment method, and has extremely high engineering practical value for improving the service performance of the crystal element in a strong laser extreme service environment.

While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this description, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as described herein. Furthermore, it should be noted that the language used in the specification has been principally selected for readability and instructional purposes, and may not have been selected to delineate or circumscribe the inventive subject matter. Accordingly, many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the appended claims. The present invention has been disclosed in an illustrative rather than a restrictive sense, and the scope of the present invention is defined by the appended claims.