Yande XU

Graduate School of Science and Technology, Niigata University, 8050 Ikarashi 2, Niigata 950-2181, Japan

(Received April 13, 2004; Accepted July 6, 2004; Revised May 28, 2004)

This paper proposes a new measuring method called two-period interference fringe interferometry, for a step-profile altitude difference measurement. The principle of the method is different from that of the two-wavelength interferometry which is widely known. The two interference fringes with only slight difference between their spatial periods are obtained by turning a binary step-grating, and they produce a synthetic equivalent period much longer than either of the two periods alone. The interference fringes are produced by the ± 1st-order beams diffracted from the grating. The intensity distribution of the interference pattern is independent of the wavelength of the laser-diode light source used. The measuring range of this method is much larger than that of the two-wavelength interferometery. Sinusoidal phase modulating technique is easily applied to detect the phase distribution of the interference pattern by vibrating the grating sinusoidally. A plane reflector of ~3 mm thickness is measured to verify this novel method.

Key words: interferometry, grating, interference fringe, step-profile, sinusoidal phase modulating