Analysis of laser source birefringence and dichroism on nonlinearity in heterodyne interferometry

This work addresses the problem of how birefringence and dichroism within a laser source affect the linearity in heterodyne interferometry. A previous paper showed that of the two, only dichroism is responsible for nonlinearity in a perfect heterodyne interferometer. However, this new analysis shows that this is not so, and further offers a new expression for the resulting nonlinearity. For perfect optical components external to the laser source the nonlinearity is approximately equal to the extent of the non-orthogonality between the major axes of the elliptical modes, provided that birefringence is small.