Thomas W. Dey

Wide-range, high-accuracy, white light piston sensor for segmented optics

Optical systems with segmented mirrors require precision coalignment of their segments to attain the desired performance. A novel sensor for measuring piston over a ± 10 wave range by analyzing the image of a white light point source is described. The sensor combines a Youngs two-slit aperture pair for coarse sensing with another set of apertures, which include a phase retardation portion for fine sensing. The course sensor has an accuracy of ± 0.25 wave over the full range. The fine sensor works within ± 0.5 wave of zero with ± 0.005 wave accuracy, and a repeatability of the order of ± 0.001 wave. Theoretical derivation and experimental results are provided.

High-accuracy white-light optical piston sensor for segmented optics

A novel piston sensing concept is described for measuring piston over the +/- 0.5 wave range. The image of a white light point source is optically processed using a half-wave phase plate to enhance the presence of piston in the incident wavefront. The resultant point spread function is recorded on a CCD camera and analyzed using a simple intensity balance algorithm. Theoretical derivation and experimental results are provided, with emphasis on piston values below 0.25 waves. Piston values are measured to +/- 1/200 wave accuracy or better with a repeatability on the order of +/- 1/1000 wave.