JPH0579462B2 - - Google Patents

Description

Detailed Description of the Invention The present invention provides soft crystals such as lead molybdate (PbMoO ₄ ) single crystal (hereinafter abbreviated as PbMoO ₄ crystal) used in acousto-optic devices such as ultrasonic optical deflectors.
The present invention relates to a polishing method for finishing the surface of a mirror to an optically smooth surface without scratches, that is, a mirror surface.

In order to use PbMoO ₄ crystal as an acousto-optic device, a scratch-free mirror surface that does not interfere with laser light transmission or ultrasonic oscillation is required, but PbMoO ₄ crystal has not been artificially developed. Since it has only been a short time since then, there has been little research on mirror finishing technology. As a polishing method for crystals for optical elements, such as TeO ₂ , which have similar properties to PbMoO ₄ crystals,
Conventionally, a method combining a lapping process and a pitch polishing process has been used. That is, Al ₂ O ₃ and SiC
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 and a liquid such as water or oil to correct the dimensions and flatness.
This is a polishing process in which a mirror finish is created on a pitch board using a polishing agent that is a mixture of abrasive grains such as CeO ₂ and Fe ₂ O ₃ and liquids such as water and oil. Among these polishing methods, when the processing method using water was applied to PbMoO ₄ crystals, the wrapping process was carried out without any problems, but a scratch-free mirror surface could not be obtained in the polishing process.

Although the reason for this is not clear, it is thought that the processing mechanism differs due to the difference in deliquescent properties and melting points of the crystals. In other words, in the case of TeO ₂ crystal, the hardness at the crystal surface is considerably softer than the hardness of the crystal itself (Mohs hardness: 5) due to its deliquescent property; ₂ or Fe ₂
Even with O ₃ abrasive grains (Mohs hardness: 6), processing proceeds due to plastic flow action, whereas PbMoO ₄ crystals (Mohs hardness: 3) are not deliquescent and have a melting point of 1060°C (the melting point of TeO ₂ Since the temperature is quite high (733℃), it is assumed that a mirror surface cannot be obtained because no plastic flow phenomenon occurs.

Processing methods using oil can provide mirror surfaces without scratches, but they have the disadvantage of 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 it is an object of the present invention to provide a method for polishing soft crystals in which a scratch-free mirror surface can be easily obtained by the micro-cutting action of the tips of highly hard diamond abrasive grains.

Examples according to the present invention will be described below regarding PbMoO ₄ crystals.

Example 1 A PbMoO ₄ crystal material is cut into blocks with dimensions of 10 x 20 x 30 mm using, for example, an internal cutting wheel.
Approximately 60 μm of the cutting strain layer and surface irregularities on each surface of this block body are removed by wrapping to create a flat matte surface with a surface roughness of approximately 1.0 μm. This wrapping is performed on the Sn plate using a lapping agent that is a mixture of SiC abrasive grains with a grain size of 5 μm and water, for example. Diamond 1μm surface roughness caused by wrapping
Using a polishing agent containing about 1.3% (weight ratio) of abrasive grains in pure water, remove approximately 20 μm by polishing on a Sn board with concentric grooves. 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, use a polishing agent containing 1μm diamond abrasive grains diluted to 1.3% with pure water to remove scratches that have occurred on the polished surface.
For example, polish it on a K-3 pitch plate with lattice grooves to approximately 4 μm.
Remove. Thereafter, the supply of the polishing agent containing diamond abrasive grains is stopped, and polishing is carried out on the K-3 pitch plate described above while supplying only pure water to remove approximately 1 to 2 μm. At this time, a mirror surface with no minute scratches was achieved, and the best surface for processing an acousto-optic element was obtained. Furthermore, even when the pitch polishing with the aforementioned diamond abrasive grains was processed to a depth of 6 μm, a mirror surface with no scratches was achieved by further performing pitch polishing with pure water only.

In the above example, nothing was mentioned about both positions of the PbMoO ₄ crystal, (100), (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 PbMoO ₄ 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 PbMoO ₄ crystal, which was difficult with conventional polishing techniques, can be easily achieved, and an acousto-optical process using a crystal material having a composition and properties similar to PbMoO ₄ crystal can be achieved. This is an extremely effective polishing technique for manufacturing devices.

Claims (1)

[Claims] 1. After cutting a crystal material into a predetermined shape, the surface of a mechanically wrapped block crystal is subjected to the following steps (1), (2), and (3) in order. A method for polishing soft crystals characterized by mirror finishing. (1) A polishing process that uses a combination of a soft metal polisher and a polishing agent made by mixing diamond abrasive grains with pure water. (2) A pitch polishing process using a combination of pitch polisher and a polishing agent made by mixing diamond abrasive grains with pure water. (3) Water polishing process using a combination of pitch polisher with diamond abrasive grains left in step (2) and pure water.