Single frequency laser interferometer with subnanometer accuracy

摘要

In this paper, the dynamic compensation of nonlinearity of a laser interferometer with a quadrature fringe detecting system is described. The computer measures the nonlinearity arising from unequal amplitudes and offsets in the detection system. Two phase-quadrature signals are corrected and processed for elliptical fitting with a least-square method. The DC offsets, the AC amplitudes and the phase term can be determined. These values are feedback to auto gain control circuit to minimise an elliptical distortion. Computer automatically controls all electronic adjustments. Experimental results demonstrate that nonlinear free interferometer can be easily achieved.