Testing of nonlinear diamond-turned reflaxicons

The extreme alignment sensitivity of nonlinear diamond-turned reflaxicons makes them difficult to test and analyze. To evaluate the wave front it is necessary to know what portion results from alignment errors. This paper describes the setup, alignment, and testing of a nonlinear diamond-turned independent-element reflaxicon manufactured at the Union Carbide, Oak Ridge Y-12 plant. Interferograms taken with the center cone misaligned a known amount are analyzed using the axicon preprocessing option in FRINGE [J. S. Loomis (ASTM Report STP 666 and Proc. Soc. Photo-Opt. Instrum. Eng. 171, 64 (1979)]. The results show that FRINGE correctly removes the cone and decenter errors introduced by the misalignments. It is also shown how the resulting interferograms are unfolded to give the OPD errors as seen on the outer cone.