We present a method for the calibration of a spatially phase-shifted digital speckle pattern interferometer (SPS–DSPI), which was designed and built for the purpose of testing the James Webb space telescope (JWST) optical structures and related technology development structures. The need to measure dynamic deformations of large, diffuse structures to nanometer accuracy at cryogenic temperature is paramount in the characterization of a large diameter space and terrestrial based telescopes. The techniques described herein apply to any situation, in which high accuracy measurement of diffuse structures are required. The calibration of the instrument is done using a single-crystal silicon gauge. The gauge has four islands of different heights that change in a predictable manner as a function of temperature. The SPS–DSPI is used to measure the relative piston between the islands as the temperature of the gauge is changed. The measurement results are then compared with the theoretical changes in the height of the gauge islands. The maximum deviation of the measured rate of change of the relative piston in nm∕K from the expected value is 3.3%.
© 2007 Optical Society of America
Instrumentation, Measurement, and Metrology
Original Manuscript: January 24, 2007
Revised Manuscript: May 14, 2007
Manuscript Accepted: May 15, 2007
Published: August 8, 2007
Babak Saif, Bente Hoffmann Eegholm, Marcel Bluth, Perry Greenfield, Warren Hack, Peter Blake, Ritva Keski-Kuha, and Michael North-Morris, "Calibration of spatially phase-shifted DSPI for measurement of large structures," Appl. Opt. 46, 5622-5630 (2007)