Gauge block calibration by using a high speed phase shifting interferometer comprising two frequency scanning diode lasers

摘要

We developed a gauge block interferometer which utilizes the frequency tunable laser diodes as both light sources and phase shifters of a phase shifting interferometer. By using a confocal Fabry-Perot cavity made of ultra low expansion glass, and linearly modulating the laser diode current, the laser frequency could be injection locked to the resonant modes of the Fabry-Perot cavity consecutively. These equal spaced frequencies produce equally phase shifted interferometric images which are ideal to be analyzed by the Carre algorithm. Two frequency scanning lasers at the wavelengths of 636 nm and 657 nm are used as light sources for the gauge block interferometer. The system takes only 10 ms for a single measurement which acquires two sets of four equally phase shifted images with 640×480 pixels in size. Central lengths of gauge blocks are measured by using the phase shifting interferometry and exact fraction method. The performance of the high speed interferometer could be checked by comparing the measurement results on the same gauge block made by two different methods. Two results agreed well within the measurement uncertainty.