Ultrafast laser stress figuring for accurate deformation of thin mirrors

TL;DR

This paper introduces ultrafast laser stress figuring (ULSF), a scalable and precise method for shaping thin mirrors by applying focused ultrafast laser stress, achieving nanometer-level accuracy without compromising higher-spatial frequency errors.

Contribution

The paper presents ULSF as a novel, scalable technique for accurately shaping thin mirrors with minimal impact on high-frequency errors, suitable for post-coating application and high throughput.

Findings

Achieved 10-20 nm RMS correction over 28 Zernike terms in four mirrors.

Stable optical performance over a month for dielectric-coated mirrors.

Potential for high-throughput, accurate freeform mirror shaping using laser technology.

Abstract

Fabricating freeform mirrors relies on accurate optical figuring processes capable of arbitrarily modifying low-spatial frequency height without creating higher-spatial frequency errors. We present a scalable process to accurately figure thin mirrors using stress generated by a focused ultrafast laser. We applied ultrafast laser stress figuring (ULSF) to four thin fused silica mirrors to correct them to 10-20 nm RMS over 28 Zernike terms, in 2-3 iterations, without significantly affecting higher-frequency errors. We measured the mirrors over a month and found that dielectric-coated mirrors were stable but stability of aluminum-coated mirrors was inconclusive. The accuracy and throughput for ULSF is on par with existing deterministic figuring processes, yet ULSF doesn't significantly affect mid-spatial frequency errors, can be applied after mirror coating, and can scale to higher throughput using mature laser processing technologies. ULSF offers new potential to rapidly and accurately shape freeform mirrors.