Analysis of nonlinearity in a high-resolution grating interferometer

Metrological feasibilities of a high-resolution grating interferometer (GI) based on a transverse Zeeman laser are investigated. When the grating pitc h equals 20 mu m, a resolution of 0.7 nm is obtained by means of a heterody ne signal processing method. The comparison of two approaches for determini ng the residual nonlinearity is presented. One is to evaluate the maximum r esidual error by determining the amplitude modulation degree of the measure ment signal. The other is to do a high precision calibration with a differe ntial dual-frequency interferometer that has a higher precision. The experi mental results show that the nonlinearity is no more than 25 nm which fits well with the estimating result. Analysis of the depolarization effect of t he grating indicates that it has little influence on the measurement accura cy. (C) 2000 Elsevier Science Ltd. All rights reserved.