Abstract

The practical method for measuring displacement with laser interferometric system is proposed. The newly developed interferometric system has a simplified optical layout, less number of optical elements and a shortened optical pass. As a result, the thermal drift and nonlinearity in the displacement measurement has been decreased in both the bifrequency heterodyne system and the fringe-counting system. In addition, simplified electrical fringe counting logic has made it faster to get the measured value without losing any accuracy in fringe counting, and to calculate the corrected light wavelength by the subtraction of the two fringes' value. This two-fringe value system can make the displacement measurement more precise than single value system, and would be more useful for the position feedback system. This method achieved (1) subnanometer resolution [less than (λ)/1000], (2) 5 MHz throughput of the differential light wavelength compensated value and (3) nonlinearity within (λ)/1000.

© 1990 Optical Society of America