A method for planarizing the optical surface of potassium dihydrogen phosphate crystal

Abstract

The invention relates to an optical element surface planarization method. The method mainly focuses on potassium dihydrogen phosphate (KH2PO4, also known as KDP) nonlinear optical crystal material after turning of a single point diamond lathe as a processing target, with the method of ion beam sputtering deposition, a layer of film of silicon or silicon dioxide or the composite of silicon dioxide and silicon is deposited on the optical surface of the potassium dihydrogen phosphate optical crystal material, and then after vacuum cooling, a layer of silicon film or silicon dioxide film or silicon dioxide and silicon composite film with low surface roughness is formed on the surface of the potassium dihydrogen phosphate optical crystal material, wherein the upper surface of the film layer is a flattened surface. According to the optical element surface planarization method, a layer of silicon film or silicon dioxide film or silicon dioxide and silicon composite film with good mechanical properties, stable properties, low surface roughness and compactness is formed on the surface of the potassium dihydrogen phosphate optical crystal material, the technological process is simple, the surface of the potassium dihydrogen phosphate can achieve a good planarization effect in a low-temperature vacuum environment, and a good foundation is made for later ion beam polishing of potassium dihydrogen phosphate crystals.

Description

technical field [0001] The invention belongs to the technical field of surface planarization of optical elements, in particular to potassium dihydrogen phosphate (KH 2 PO 4 ) method for flattening crystal-like optical surfaces. Background technique [0002] Potassium dihydrogen phosphate (KH 2 PO 4 Also known as KDP) is a good nonlinear optical material and piezoelectric material, which has a large nonlinear optical coefficient, a low optical absorption coefficient and a high laser damage threshold. It is widely used in high-power laser system controlled thermonuclear reaction, nuclear explosion simulation, etc. It is the only crystal material that can be used in inertial confinement fusion ICF laser engineering, mainly for frequency doubling, photoelectric modulation and electro-optic switch. [0003] However, potassium dihydrogen phosphate (KH 2 PO 4 ) crystals have the characteristics of brittleness, deliquescence, large thermal expansion coefficient, and sensitivit...

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Problems solved by technology

[0003] However, potassium dihydrogen phosphate (KH 2 PO 4 ) crystals have the characteristics of brittleness, deliquescence, large thermal expansion coefficient, and sensitivity to temperature changes, which brings great difficulties to high-quality processing and has become one of the most difficult to process optical parts currently recognized.

Potassium dihydrogen phosphate (KH 2 PO 4 ) crystal-like optical crystal parts, if the periodic small-scale ripples and other defects are not eliminated, the surface roughness will not meet the requirements, which will affect the light transmission performance of the parts, causing light to be consumed in the optical path by scattering or other forms , so that the laser output energy and energy density are low during laser targeting, and potassium dihydrogen phosphate (KH 2 PO 4 ) crystal advantage

[0004] Potassium dihydrogen phosphate (KH) is currently used at home and abroad 2 PO 4 ) crystal-like processing and polishing methods include single-point diamond turning (SPDT), ultra-precision grinding, magnetorheological polishing, crystal micro-water mist dissolution polishing, etc. These methods inevitably give potassium dihydrogen phosphate (KH 2 PO 4 ) crystalloids cause a certain degree of subsurface damage, which in turn affects their role in optical engineering

Among the many processing methods, the mainstream processing method is single-point diamond turning, and the small-scale ripples produced by it will affect the potassium dihydrogen phosphate (KH 2 PO 4 ) optical surface quality of the crystal

And it will bring difficulty to the further polishing process in the later stage so that the surface quality cannot be guaranteed

[0005] As an important process technology, spin coating is used in many industrial fields. At present, most of the planarization methods of potassium dihydrogen phosphate (KH2PO4) optical crystal materials use spin coating, but whether it is the surface The spin coating method used for the modified layer or the surface sacrificial layer has the following disadvantages: ①Spin coating materials generally use liquid polymer glue, most of which are volatile and their stability is affected by the environment, thus limiting the choice of planarization materials. Select the flattening material that the solid phase is less affected by the environment, the present invention can select silicon, silicon dioxide; 2. the spin-coating method that can be checked at present is only used on the optical element of small aperture, as: at 50 * 50 * 10mm 2 A planarized layer with a surface roughness of about 1.25nm and edge effects is obtained by spin coating on the KDP, and the edge effect is more significant for large-aperture optical components; ③The planarized layer made by the spin coating process is easy to produce low frequency Error; ④Because of the spin coating equipment, the spin coating process is not easy to prepare a planarization layer in batches; ⑤The spin coating process is difficult to achieve uniform planarization of spherical and aspheric optical elements

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