Interferometry is not adequate for surface measurement of large mirrors during the early stages of figuring. Edges tend to roll off with errors of many waves, and these errors are undetectable with interferometry. The Hartmann test has become very important in providing surface information during these early stages, but unfortunately, data reduction is quite slow. Itek now has an instrument to automate the Hartmann test using a scanning laser beam and a solid state sensor. A narrow laser beam scans the testpiece in an appropriate raster. A solid state detector senses the reflected spot in the vicinity of the center of curvature. Knowing the positioning of the beam, and the position of the reflected spot is sufficient information for a mirror slope determination of that raster position. A computer program integrates the slope data to produce a surface wavemap of the testpiece. This wavemap can be displayed on a contour plot within a few minutes or routed to a computer controlled Milacron robot to appropriately refigure the testpiece. A null lens is unnecessary. The measurement accuracy of the instrument is about 1/5 to 1/2 waves surface rms

Date Published: 26 March 1992
PDF: 8 pages
Proc. SPIE 1618, Large Optics II, (26 March 1992); doi: 10.1117/12.58046

Published in SPIE Proceedings Vol. 1618:
Large Optics II
Robert E. Parks, Editor(s)