Ji-Yuan LIU,¹ Ichirou YAMAGUCHI,^1,2 Jun-ichi KATO² and Toshinori NAKAJIMA²

¹Graduate School of Science and Engineering, Saitama University, 255, Shimo-Okubo, Urawa, Saitama, 338 Japan, ²Optical Engineering Laboratory, The Institute of Physical and Chemical Research (RIKEN), 2-1, Hirosawa, Wako, Saitama, 351-01 Japan

(Received August 13, 1996; Accepted October 16, 1996)

We have succeeded in video rate analysis of fringes stabilized by an active interferometer placed outside optical benches. The interferometer uses the closed loop control of injection current of a laser diode to compensate for fringe movement that is detected by a spatial filtering detector. A video image of the locked fringes with tilt is supplied to the real-time fringe analyzer that delivers unwrapped phase distribution from the three phase shifted fringes generated by the electronic moirEmethod. For a concave mirror of 130 mm diameter placed on a wooden desk we observed the repeatability of λ/60 for P-V surface error of λ/5.

Key words : surface measurement, active interferometer, real-time fringe analysis, current modulation of laser diode, feedback control