An interferometer based on the differential heterodyne configuration and wavelength-scanning interferometry for measuring large step heights is presented. The proposed interferometer is less sensitive to environmental disturbances than other interferometers and can accurately measure interference phases. A tunable diode laser is utilized to illuminate the interferometer and thus solve the phase ambiguity problem. Counting the interference fringes as the wavelength is scanned through a known change in wavelength directly determines the step height. Three gauge blocks of different lengths, 5, 10, and 50 mm, are individually wrung on a steel plate to simulate large step heights. Comparing the results measured by the proposed interferometer with those by the gauge block interferometer reveals that the accuracy is approximately 100 nm.
© 2002 Optical Society of America
Original Manuscript: January 11, 2002
Revised Manuscript: June 20, 2002
Published: October 1, 2002
Sheng-Hua Lu, Ching-I Chiueh, and Cheng-Chung Lee, "Differential wavelength-scanning heterodyne interferometer for measuring large step height," Appl. Opt. 41, 5866-5871 (2002)