Inspection of linear axicon surface by double-pass interferometry

A novel and simple double-pass interferometer is proposed for the inspection of linear axicon surfaces by leveraging their rotational symmetry. We demonstrate that positioning a flat mirror at the waist of the depth of focus ensures perfect overlap between the incoming and reflected beams, enabling a double-pass configuration. This position is confirmed to be located at half the depth of focus of the linear axicon, measured from the first focal point. The proposed configuration is integrated with a Michelson interferometer to inspect commercial off-the-shelf axicons. The measurement results show agreement with the specifications provided by the manufacturer.