METHOD AND APPARATUS FOR OPTICAL INTERFEROMETRIC MEASUREMENTS WITH REDUCED SENSITIVITY TO VIBRATION

A method and system for providing interferometric measurements having reduced sensitivity to vibrations. An interference pattern from an interferometer (35) is amplitude split into first and second interferograms and imaged onto first and second detectors (10, 11), respectively, such as CCD cameras (10, 11). The two cameras (10, 11) have different data acquisition rates. The frame integration period of the slow detector is distinctly shorter than that of the fast detector. The detectors (10,11) are disposed such that the image fields substantially overlap and are synchronized with each other for enhancing vibration insensitivity. The shorter the integration period of the slow detector with respect to the fast detector, the greater the vibration insensitivity. During data acquisition a phase shifter (45) changes the phase difference between the beams in the interferometer (35) while data from both cameras (10, 11) is taken by a frame grabber (15) and saved in a computer (25). During data analysis, the phase at each image point on each frame of the fast data set is calculated by the computer (25), with the phase difference between interferograms in the slow data set being determined from the phases derived from the fast data set and with the slow data set then being analyzed for phase at each image point using the measured phase increments.