Transmission spheres used in interferometry are specified by f-number and source wavelength. In this paper, we explore a broadband variable transmission sphere (BVTS) system based on freeform Alvarez lenses that enables variable operation across a broad range of f-numbers and wavelengths. Potential applications and performance tradeoffs are discussed in comparison to conventional spherical transmission spheres. Simulation results are presented for f/15 to f/80 configurations from visible to long-wave infrared sources in a Fizeau interferometer. Simulation results highlight that spherical, coma, and astigmatism impose limits on surface measurement quality.
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.
Conventional interferometric transmission spheres are limited by f-number and design source wavelength. We discuss a broadband variable transmission sphere system based on relative lateral translation of freeform surface pairs.
We present a broadband variable transmission sphere for Fizeau interferometry based on Alvarez lenses. The simulated system performance is compared to conventional transmission spheres for measurement of spherical surfaces.
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