Infra-red interferometer for optical testing

摘要

An infra-red interferometer for testing optical elements and assemblies in their operational wavelength band is described. The interferometer is a phase-shifting, LUPI-style Twyman-Green interferometer operating at a wavelength of 3.392 μm. The system is designed for optical testing in a vacuum chamber. For that purpose the interferometer is contained in a hermetic, vacuum-compatible enclosure, and all internal alignment functions are remotely controlled. The light source is an infra-red HeNe-laser at 3.392 μm. The camera sensing the interferograms consists of a PtSi CCD-array with 256x256 pixels. For operating the system in a vibration environment, short exposure pulses are generated from the laser light. In addition, a specialized phase-shifting data acquisition and reduction algorithm is employed which senses the random phase shifts and adapts the phase algorithm accordingly. A vacuum compatible diverger (f/2.5) and beam expander (250mm beam diameter) allow for a wide variety of optical testing configurations. Measurement results and system performance parameters are presented.