Steven R. Patterson

Design and testing of a fast tool servo for diamond turning

Abstract A self-contained and independently servo-operated diamond tool holder was built to increase the resolution and accuracy of a precision lathe. Its static and dynamic repeatability over a range of ± 50 μin (1.27 μm) is better than 0.05 μin (1.3 nm). Its frequency distortion from 0–100 Hz is less than 1.0 μin (25 nm) for a peak displacement of less than 28 μin (0.71 μm).

DESIGN AND CONSTRUCTION OF A LARGE, VERTICAL AXIS DIAMOND TURNING MACHINE

A 64-inch swing, vertical spindle axis precision lathe has been constructed. The machine incorporates a multiple-path laser feedback system, capacitance gauges, a 32-bit computer and capstan drives to provide two axes of tool motion in a 32-inch radius by 20-inch length working volume. Dimensional stability of critical components is achieved through the use of low coefficient-of-thermal-expansion materials and temperature-controlled heat sinks. Projected accuracy of the machine is approximately one microinch rms.

Improvement of absolute accuracy for a multiple bounce reflectometer through a detailed effort to reduce systematic errors.

We have constructed a multiple-bounce reflectometer similar to the one designed by Kelsall. Systematic errors present the reflectivities measured on our multiple-bounce reflectometer have been significantly reduced for high-reflectivity mirrors. This reduction came about through careful study of all components in our system. The diffraction effects of the apertures in the reflectometer were studied with the aid of a computer program that calculated the radial intensity distribution due to the Fresnel diffraction from each aperture. The systematic errors arising from the attempt to measure a concave spherical mirror were studied and minimized. A second computer program calculated the systematic error introduced by pathlength changes as the number of bounces in the reflectometer increased. The replacement of the sample thermopile detector with a thin-film bolometer along with other equipment changes has improved the absolute accuracy to 0.001 for the measured reflectivities with a demonstrated precision of 0.0003. Previous measurements had been about 0.008 low compared to measurements on the V-W pass reflectometer at China Lake, California.

Direct Machining Of A Non-Axisymmetric Phase Corrector

One of the most challenging optical components to fabricate is a non-axisymetric part. We at Lawrence Livermore National Laboratory recently used the Large Optics Diamond Turning Machine, (LODTM), to make a part called a phase corrector. The Phase corrector is an annular opical component that is used to generate a known spectrum of time varying aberration. If the corrector has the proper distribution of spatial frequencies and amplitudes it will function correctly. Since the frequencies and amplitudes were the important requirement on the surface figure, the surface of the part was specified in the Fourier domain. A surface profile was generated from the spectrum which contained spatial frequencies as high as 40 cycles per revolution. The spatial frequency maps into a time domain frequency for the z- axis tool bar that is dependent on the spindle speed. At 40 cycles per revolution, any reasonable spindle speed taxed the band width limits of the z-axis tool bar. In order to decrease the errors in the surface figure due to machine dynamics, a technique for compensating for the dynamics in the Fourier domain was developed. The non-axisymetric phase corrector was directly machined out of brass on the LODTM. Test measurements of the surface figure were made with an LVDT on LODTM and compared to the commanded profile both in the spatial and frequency domains. The surface quality was measured with a Wyco Model 1000P surface analyzer.

Wave-front correctors by diamond turning

The production of wave-front correctors by single-point diamond turning is reported. Interferograms are shown which demonstrate excellent agreement between the diamond-turned surface and the desired surface. It is concluded from this experiment that it is now feasible by means of single-point diamond turning to make generalized wave-front control surfaces or to produce any unusual surface desired by the optical designer. The maximum departure from the nearest regular surface is set by the dynamic range and maximum diamond point acceleration permitted by the machine.

Diamond Machining And Mechanical Inspection Of Optical Components

Displacement measurement and motion control are discussed for rotary and linear axes of motion, as necessary for the dimensional measurement and diamond-tool machining of grazing incidence x-ray optics. Examples of available performance levels are drawn from measurements made on current developmental hardware, and are coupled with speculation on possible future extensions.