Direct Machining Of A Non-Axisymmetric Phase Corrector

Abstract

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.