Abstract
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.
Highlights
In order to measure a convex surface, the focal length of the broadband variable transmission sphere (BVTS) must be greater than the radius of curvature (ROC) of the test surface, as illustrated in evaluated for 100 mm-diameter test surfaces
Since the BVTS entrance pupil diameter (EPD) is larger than the test surface diameter, an f/80 configuration can be used to measure a convex r/80 test surface
The results with the smallest errors in the simulated height maps were seen with IR source wavelengths in the range of f/15 to f/80
Summary
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