Fabrication of optics by use of plasma chemical vaporization machining with a pipe electrode

Abstract

We figure optical surfaces by plasma chemical vaporization machining (CVM) with a pipe electrode, in which an rf plasma generated at the electrode tip under approximately atmospheric pressure moves over the surfaces. We propose a shaping method in which the movement of plasma on the surfaces can be determined. Flat and aspheric surfaces are successfully figured with the desired peak-to-valley shape accuracy of 0.1 microm. The root-mean-square roughness of the resultant surfaces is at the subnanometer level. These results confirm that the plasma CVM and the shaping method have the capability to fabricate optics with high accuracy.

Innovations in optics manufacturing

“…It is important that the angle of the nozzle be automatically adjusted to maintain normal incidence of the plasma on the surface during scans. Manufacture of a 160 mm diameter fused silica asphere was recently reported [5], where 0.5 µm of departure was introduced into a best fit sphere (404 mm radius of curvature) with a series of 3 runs. After 3.8 h of total processing time, figure error was reduced to 130 nm p-v / 17 nm rms, and final rms surface roughness was 0.37 nm (line-scan over 250 µm).…”

Shape correction of optical surfaces using plasma chemical vaporization machining with a hemispherical tip electrode

“…Several high-precision removal methods based on chemical reactions that use plasma have been proposed [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. One such method is plasma chemical vaporization machining (CVM) proposed by Mori et al [11], which uses an rf plasma generated close to an electrode in an atmospheric-pressure environment.…”

“…Plasma CVM allows high-speed material removal with high spatial resolution because the plasma generation is confined to the proximity of an electrode under atmospheric pressure. In the plasma CVM, various types of electrodes, such as a wire electrode [11], a plane electrode [11], a rotary electrode [12][13][14][15], and a pipe electrode [16][17][18][19], are applicable to tools for high-precision fabrication. Thus, the electrode can be used in plasma CVM in a similar manner to the way tools are used in mechanical shaping methods.…”

Roughness evolution of fused silica during plasma polishing processes

“…Among the technologies, Plasma Assisted Chemical Etching (PACE), Chemical Vapor Machining (CVM) and Ion Beam Finishing (IBF) have attracted more interests [1][2][3][4][5] .…”