Method and apparatus for optical interferometric measurements with reduced sensitivity to vibration

A system for providing interferometric measurements having reduced sensitivity to vibration comprising:

• a source of illumination
• interferometer means comprising an interferometric objective having a reference path and a test path, said illumination source producing a light beam for entering said interferometer for providing a light beam along each of said paths which combine at the output of said interferometer means to produce an interferogram;
• phase shifting means associated with said interferometer means for varying the length of one of said paths by a controlled amount;
• beam splitter means disposed with respect to said interferometer means output for amplitude splitting said recombined interferogram into first and second imaging interferograms;
• first and second detector means each having a different data acquisition rate, said first detector means having a fast frame rate for acquiring a fast data set of interferograms and said second detector means having a slow frame rate for acquiring a slow data set of interferograms, said beam splitter means imaging said first and second imaging interferograms onto said first and second detector means respectively, said first and second detector means comprising image fields and being disposed such that said image fields substantially overlap and are synchronized with each other so that the frame imegration periods are identical and overlap in time;
• said phase shifting means changing said phase difference between beams in said interferometer means during data acquisition;
• and
• means for analyzing said fast data set of interferograms for phase, determining a phase difference between said interferograms in said slow data set from said phases derived from said fast data set, and analyzing said slow data set with said phase differences while accounting for non-equal phase separations between interferograms;
• wherein the phase separation between acquired interferograms may be dynamically measured while enabling correction of phase errors due to instrument inaccuracies and external vibrations;
• means for calculating the phase at each image point on each frame of said fast data set during data analysis and calculating a phase increment for each image point of said fast data set phases.