The micro-arcsecond metrology testbed (MAM) provides a testing ground for SIM to perform optical path difference measurements with picometer (pm) precision. Because of imperfect optics and non-ideal laser sources it is inevitable that the cyclic bias is one of the major error sources for SIM. Many experiments have been conducted to diagnose and to characterize cyclic bias in the laser gauges, and in white light fringe detection. Our data analysis indicates that cyclic bias in MAM has a predictable frequency and a relatively stable amplitude. It has been proposed to use phase measurements at different wavelengths to solve for the cyclic bias. The experiment results have shown that the cyclic bias in SAVV are reduced from nm level to the level of hundred picometers. Besides the cyclic bias the effective wavelengths of spectral channels have to be calibrated also. At present, a new method using FFT technique and new metrology gauge demonstrates that the wavelength determination has a precision of 10^-4. The spectrometer in MAM is stable. The changes of effective wavelengths in a few weeks is about one nanometer, or less. Systematic biases above must be periodically calibrated.

Date Published: 26 February 2003
PDF: 11 pages
Proc. SPIE 4852, Interferometry in Space, (26 February 2003); doi: 10.1117/12.460723

Published in SPIE Proceedings Vol. 4852:
Interferometry in Space
Michael Shao, Editor(s)