Reduction of retrace error from broadband variable transmission spheres in Fizeau interferometry

Abstract

We have previously presented broadband variable transmission sphere (BVTS) systems based on the Alvarez lens for use in Fizeau interferometry. A BVTS system may replace multiple conventional transmission spheres with one system composed of two plano-freeform optical elements. In this paper, we discuss retrace error as a source of aberrations in Fizeau interferometry measurements when using BVTS systems. We explore a design optimization method to decrease retrace error by optimizing freeform surfaces to reduce targeted Fringe Zernike wavefront aberrations. Significant reduction in peak-to-valley retrace error is demonstrated.