JPS5919664A - Soft crystal polishing method - Google Patents

Abstract

PURPOSE:To make it possible to planish soft crystal by subjecting the surface of a block crystal body subjected to lapping to polishing and pitch grinding in combination with aqueous diamond abrasive grains in polishing of the soft crystal for an acoustooptic element. CONSTITUTION:For example, a PbMoO4 crystal raw material is cut into a block body by means of an internal periphery cutting blade cutting grindstone, and the surface of said block body is subjected to lapping to provide its flat satin-like surface with its roughness of about 1.0mum. Then, said roughly finished surface is cut away by about 20mum by polishing it on an Sn plate provided with a concentric groove by making use of a polishing agent obtained by mixing 1mum diamond abrasive grains into pure water by 1.3% of said grains against the pure water. Then, when subjecting scratches produced in the polishing surface to pitch grinding on a K-3 pitch plate equipped with grid-shaped grooves using a polishing agent obtained by diluting 1mum diamond abrasive grains by pure water to the concentration of said grains 1.3% to remove said surface by about 6mum, this surface provides a specular surface posessing only several lines of scratches per the surface.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a scratch-free optical coating for the surface of soft crystals such as lead molybdate (PbMo04) single crystals (hereinafter abbreviated as PbMoO4 crystals) used in acousto-optic devices such as ultrasonic light polarizers. The present invention relates to a polishing method for finishing a smooth surface, that is, a mirror surface.

P b FT'lOO< In order to use a crystal as an acousto-optic element, a scratch-free mirror surface is required that does not interfere with the transmission of laser light or the emission of ultrasonic waves.
Since PbMoO4 crystals have only recently been artificially developed, there has been little research into mirror finishing technology.

Conventionally, a method combining a lapping process and a pitch polishing process has been used as a method for polishing crystals for optical elements, such as Te 2 O, which have properties similar to PbMo0a crystals. In other words, the lapping process involves mechanically polishing a glass or cast iron plate using a lapping agent that is a mixture of abrasive grains such as AJ, O, or SiC and liquids such as water or oil to correct the dimensions and flatness. This is a polishing process in which mirror polishing is performed on a pitch plate using a polishing agent that is a mixture of abrasive grains such as CeO, Fe, O, etc., and a liquid such as water or oil. Among these polishing methods, when the processing method using water was applied to Pb Mo O 4 crystal, the lapping process was performed without any problems, but a scratch-free mirror surface could not be obtained in the polishing process.

The reason for this is not clear, but it is thought that the curing mechanism is different due to the difference in deliquescent properties and melting points of the crystals.

In other words, in the case of Tea, crystals have deliquescent properties, so the hardness at the surface of the crystal is the hardness of the crystal itself, Mohs hardness: Even with CeO, Fe, O, abrasive grains (Mohs hardness 26), processing proceeds due to plastic flow action, whereas PbM
In the case of oO4 crystal (Mohs hardness: 3), it is not deliquescent and has a melting point of 1060'c (TeO, (7) melting point is 733'c
), it is assumed that a mirror surface cannot be obtained because the plastic flow phenomenon does not occur.

Processing methods using oil can provide mirror surfaces without scratches, but they have drawbacks such as poor workability, such as cleaning of crystals after processing and disposal of polishing agents.

The object of the present invention was made in view of the above circumstances, and is to provide a method for polishing soft crystals that can easily obtain a mirror surface without scratches through the micro-cutting action of the tips of highly hard diamond abrasive grains. be.

Examples according to the present invention will be described below using PbMoO4 crystals.

Example 1 pl)Mo04. The crystal material is cut into blocks with dimensions of 10 x 20 x 30 mm, for example, using an internal cutting wheel.

The cutting strain layer and surface irregularities on each surface of this block body were removed by approximately 60 μm by lapping, and the surface roughness was reduced to 1.
Create a flat pear surface with a thickness of about 0 μm. This lapping is performed on the Sn plate using, for example, a lapping agent that is a mixture of SIC abrasive grains with a particle size of 5 μm and water. The surface roughness caused by lapping can be removed by using a polishing agent containing 1 μm diamond abrasive grains mixed with pure water at about 1.3% (weight ratio).
Approximately 20 μm is removed by boring on the plate. Visually, the polished surface has a mirror surface with a surface roughness of 0.01 to 0.02 μm, but there are countless minute scratches. Next, the scratches occurring on the boring surface are polished to about 6 μm using a polishing agent made by diluting 1 μm diamond abrasive grains to 1.3% with pure water, for example, on a 13-pitch plate with lattice grooves.
Remove. At this time, the surface had a mirror surface with only a few minute scratches and was fully usable as a processed surface for acousto-optic devices.

Example 2 A block body cut from a PbMoO crystal material is polished in the same manner as in Example 1 through a lapping process and a polishing process. Next, about 4 μm of scratches generated on the boring surface are removed by polishing on a 13-pitch plate with lattice grooves, for example, using a polishing agent prepared by diluting 1 μm diamond abrasive grains with pure water to a ratio of 1.3. After this, the supply of the polishing agent containing diamond abrasive grains was stopped, and while supplying only pure water, the above-mentioned surface was polished on a 13-pitch plate to approximately 1 to 2 μm.
Remove n1. At this time, a mirror surface with no minute scratches was achieved, and the best surface for processing an acousto-optic element was obtained. Further, even when the pitch polishing amount using diamond abrasive grains was 6 μm as in Example 1, a mirror surface with no cis scratches was achieved by further performing pitch polishing using only pure water.

In the above example, nothing was mentioned about the plane orientation of the PbMoO4 crystal, but (100) and (010)
.

Mirror finishing has been achieved not only on the (001) surface but also on other surfaces.

Further, in the above embodiment, the case of PbMoO4 crystal was described, but the present invention may be applicable to other soft crystal materials.

As described above, according to the present invention, mirror polishing of PbMoO4 crystal, which was difficult with conventional polishing techniques, can be easily achieved, and acoustic polishing using a crystal polishing material having a composition and properties similar to those of PbMoO4 crystal can be achieved. This is an extremely effective polishing technique for manufacturing optical elements.

Claims (1)

[Claims] 1. After cutting the raw material crystal into a predetermined shape, the surface of the mechanically wrapped block crystal is mirror-finished according to the following steps (1) and (2) in order. A method for polishing soft crystals characterized by the following. (1) A polishing process using a combination of a soft metal polisher and water-soluble diamond abrasive grains. (2) Pitch polishing process using a combination of pitch polisher and water-soluble diamond abrasive grains. 2. After cutting the raw crystal into a predetermined shape, the surface of the mechanically wrapped block crystal is mirror-finished according to the following steps (1), (2), and (3). Characteristic soft crystal polishing method. (1) A polishing process using a combination of a soft metal polisher and water-soluble diamond abrasive grains. (2) Pitch polishing process using a combination of pitch polisher and water-soluble diamond abrasive grains. (3) A water polishing process using a combination of a pitch polisher with diamond abrasive grains embedded in its surface and pure water.