Experimental investigation of birefringence of a parabolic gradient-index lens on the basis of astigmatic transformation of a Bessel beam

A method for the investigation of birefringence of mechanically free parabolic gradient-index lenses based on the astigmatic transformation of a zero-order Bessel beam has been experimentally verified. Special features of the alignment of the optical setup are described and practical recommendations for selecting the setup components are given. By the example of a quarter-wave lens, we show experimentally that the optical path difference can be reliably measured within a 0.05$\lambda_0$ accuracy. A significant difference between the birefringence properties of the gradient-index lenses in their central and edge regions is confirmed.