Transmitted wavefront metrology of aspheric wavefronts using scanning Fizeau in...

03/10/2026

Transmitted wavefront metrology of aspheric wavefronts using scanning Fizeau interferometry

Abstract

Transmitted wavefront error (TWE) measures how much an optical system's output wavefront deviates from the wavefront prescribed by the optical designer. TWE captures system-level errors, such as assembly misalignment and mounting stresses, and directly characterizes the as-built performance of the system. Laser Fizeau interferometry is the workhorse for TWE measurement, but specialized null correctors are required to measure aberrated wavefronts that have a large departure from the ideal spherical wavefront. Computer-generated holograms remain the gold standard for testing a single component at volume; however, they are costly to design and fabricate and can be challenging to align in test setups. To address this inflexibility, scanning Fizeau interferometry-an established solution for aspheric surface metrology that does not require null correctors-was extended to measure TWE in aspheric wavefronts. The technique involves axially scanning the part under test and a reference surface within a spherical Fizeau cavity and reconstructing the TWE from annular zones of low fringe density. This was implemented on a commercial Zygo metrology platform for Fizeau interferometry and direct TWE measurements of five off-the-shelf plano-convex lenses were performed. To validate these measurements, ray-tracing simulations of the Fizeau cavity were created in Zemax OpticStudio, where independently measured as-built lens errors for each lens were supplied as inputs. The average peak-to-valley difference between the direct TWE measurements and the simulated TWE measurements was found to be less than 20 nm. This close agreement demonstrates potential for flexible and part-agnostic metrology of aspheric transmitted wavefronts-offering a practical alternative to complex and costly setups that require null correctors.

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