Proceedings PaperAutomated Phase-Measuring Interferometry With A Frequency-Modulated Laser Diode
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A Twyman-Green heterodyne interferometer with a laser diode source was constructed for testing an optical element. The wavelength induced by laser injection current is continuously changed to introduce a time-varying phase difference between the two beams of an interferometer with an unbalanced optical path length. An automated phase-measuring interferometric system was developed in which the laser current is changed to synchronize intensity data acquisition with vertical drive pulses of a charge-coupled device (CCD). The intensity of interference pattern is integrated with a CCD detector for intervals of one-quarter period of one fringe. A microcomputer calculates the phase to be detected. The experimental results are shown to measure the profile of a diamond-turned Al surface; the rms repeatability of λ/105 was obtained.