Freeform optics can reduce the cost, weight, and size of advanced imaging systems,
but it is challenging to manufacture the complex rotationally asymmetric surfaces to optical
tolerances. To address the need for disruptive, high-precision sub-aperture forming and finishing
techniques for freeform optics, we investigate an alternative, non-contact polishing methodology
using femtosecond lasers, combining modeling, experiments, and demonstrations. Femtosecondlaser-
based polishing of germanium was investigated using an experimentally-validated twotemperature
model of laser/germanium interaction to guide the understanding and selection of
laser parameters to achieve near-nonthermal ablation for polishing and figuring. For the first time
to our knowledge, model-guided femtosecond laser polishing of germanium was successfully
demonstrated, achieving precision material removal while maintaining single-digit nanometer
optical surface quality. The demonstrated femtosecond-laser-based polishing technique lays the
foundation for semiconductor optics polishing/fabrication using femtosecond lasers and opens a
viable path for high-precision, complex sub-aperture optical polishing tasks on various materials.
© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
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Femtosecond-laser-enabled simultaneous figuring and finishing of glass with a subnanometer optical surface
We demonstrate simultaneous figuring and surface finishing of glass using a femtosecond laser. For the first time, to the best of our knowledge, we have achieved deterministic material removal with nanometer precision and maintained sub-nanometer surface roughness without inducing any mid-spatial-frequency errors to the initial surface. A dynamic pulse propagation model is established to predict the interaction process, including plasma generation and surface temperature. The interactive modeling and the experiments enable the selection of a set of laser parameters to achieve controllable optical figuring and finishing. This demonstration shows the potential for using femtosecond lasers for advanced freeform optic forming, finishing, and reduction of detrimental mid-spatial-frequency errors, and laser-ablation-based patterning used for fabrication of integrated photonics and lasers.
more » « less- NSF-PAR ID:
- 10531221
- Publisher / Repository:
- Optical Society of America
- Date Published:
- Journal Name:
- Optics Letters
- Volume:
- 47
- Issue:
- 15
- ISSN:
- 0146-9592; OPLEDP
- Format(s):
- Medium: X Size: Article No. 3860
- Size(s):
- Article No. 3860
- Sponsoring Org:
- National Science Foundation
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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.
