PRECISION METROLOGY FOR A MICHELSON INTERFEROMETER

TO MAKE A MICHELSON INTERFEROMETER SPECTROMETER VIABLE AT SHORT AND VERY SHORT OPTICAL WAVELENGTHS REQUIRES A SUPERB METROLOGY SYSTEM CAPABLE OF ACQUIRING AND MAINTAINING ALIGNMENT BETWEEN MIRRORS TO A SMALL FRACTION OF THE WAVELENGTH. OPTRA HAS DEMONSTRATED THAT IN THE INFRA-RED PART OF THE SPECTRUM A METROLOGY SYSTEM BASED UPON A 2FREQUENCY-HENE LASER CAN BE HIGHLY EFFECTIVE FOR THIS PURPOSE. SUCH A LASER, IN EFFECT SIMULATES A CONSTANT, CONTINUOUS AND HIGH DIFFERENTIAL MIRROR VELOCITY WITH A VELOCITY DETERMINED BY THE LASER DIFFERENCE, BEAT OR HETERODYNE FREQUENCY. THIS MAKES IT POSSIBLE TO MEASURE MIRROR POSITION, TRAVEL AND TILT AT A RATE VIRTUALLY INDEPENDENT OF MIRROR SCAN VELOCITY AND/OR DIRECTION. OPTRA PROPOSES TO DEMONSTRATE THAT BY OPTIMIZING CAPTURE RANGE, ELECTRICAL BANDWIDTH AND RADIOMETRY THE SAME SYSTEM CAN BE APPLIED TO A VERY SHORT WAVELENGTH INTERFEROMETER AND MAINTAIN MIRROR ALIGNMENT TO THE REQUISITE SMALL FRACTION OF A WAVELENGTH. THIS WILL MAINTAIN THE INTERFEROMETER MODULATION OR CHOPPING EFFICIENCY AT A HIGH LEVEL, A FACTOR OF CRITICAL IMPORTANCE FOR ANY PHOTON NOISE LIMITED MULTIPLEX SPECTROMETER.