1 January 1992 Phase-locked laser diode interferometer
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Abstract
We propose a phase locked interferometer where tunability of the wavelength of a laser diode is utilized. A CCD image sensor detects an interference signal electrically scanning a measuring point along a surface of an object. The phase of the interference signal changes according to the surface profile. This phase is kept at a constant value by controlling the injection current of the laser diode with a feedback control system. The surface profile is obtained from the change in the injection current. The feedback signal is generated directly from the output of the CCD image sensor, which enables us to make high-speed measurements in real time. The scanning time required to complete the measurement for one measuring point was from approximately 2 msec to approximately 10 msec. External disturbances such as mechanical vibrations cause phase variations in the interference signal, and accurate measurements become impossible. Detection of the phase variation at a fixed point on the surface of the object is added to the phase locked interferometer. The feedback control of the injection current is done alternately for the fixed point and the measuring point. An exact surface profile is obtained by subtracting the phase variation detected at the fixed point from the surface profile detected at the measuring points. We could improve the measurement accuracy from approximately 20 nm to approximately 5 nm in surface profile measurements of diamond turned aluminum disks.
© (1992) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Osami Sasaki, Takamasa Suzuki, Katsuhiro Higuchi, "Phase-locked laser diode interferometer", Proc. SPIE 1553, Laser Interferometry IV: Computer-Aided Interferometry, (1 January 1992); doi: 10.1117/12.135293; https://doi.org/10.1117/12.135293
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