Ultra-high-resolution optical monitoring system using a noise cancellation technique

The feasibility of using bi-detectors or quad-detectors for ultra-high-resolution position-monitoring systems is explored. Factors that can affect the resolution of this kind of detection system are examined. We find that one of the major limiting factors is the shifting of the laser beam. A noise cancellation technique is developed successfully to suppress this noise. Using this noise cancellation system together with a thermally compensated laser and a pinhole spatial filter in a temperature- and vibration-controlled environment, the feasibility of ultrahigh resolution (<20 Angstrom) for displacement monitoring is demonstrated using off-the-shelf components. (C) 1997 Society of Photo-Optical instrumentation Engineers.