Enhancing precision in fs-laser material processing by simultaneous spatial and temporal focusing

Kammel, R., Ackermann, R., Thomas, J., Götte, J. , Skupin, S., Tünnermann, A. and Nolte, S. (2014) Enhancing precision in fs-laser material processing by simultaneous spatial and temporal focusing. Light: Science and Applications, 3(5), e169. (doi: 10.1038/lsa.2014.50)

Abstract

In recent years, femtosecond (fs)-lasers have evolved into a versatile tool for high precision micromachining of transparent materials because nonlinear absorption in the focus can result in refractive index modifications or material disruptions. However, when high pulse energies or low numerical apertures are required, nonlinear side effects such as self-focusing, filamentation or white light generation can decrease the modification quality. In this paper, we apply simultaneous spatial and temporal focusing (SSTF) to overcome these limitations. The main advantage of SSTF is that the ultrashort pulse is only formed at the focal plane, thereby confining the intensity distribution strongly to the focal volume and suppressing detrimental nonlinear side effects. Thus, we investigate the optical breakdown within a water cell by pump-probe shadowgraphy, comparing conventional focusing and SSTF under equivalent focusing conditions. The plasma formation is well confined for low pulse energies <2 µJ, but higher pulse energies lead to the filamentation and break-up of the disruptions for conventional focusing, thereby decreasing the modification quality. In contrast, plasma induced by SSTF stays well confined to the focal plane, even for high pulse energies up to 8 µJ, preventing extended filaments, side branches or break-up of the disruptions. Furthermore, while conventional focusing leads to broadband supercontinuum generation, only marginal spectral broadening is observed using SSTF. These experimental findings are in excellent agreement with numerical simulations of the nonlinear pulse propagation and interaction processes. Therefore, SSTF appears to be a powerful tool to control the processing of transparent materials, e.g., for precise ophthalmic fs-surgery.

• Item Type: Articles
• Additional Information: This study was supported by the Thuringian Ministry of Education, Science and Culture (OptiMi 2020-Graduate Research School ‘Green Photonics’, B514- 10061), the German Research Foundation (Leibniz program) and the Carl Zeiss Foundation
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Goette, Dr Joerg
• Authors: Kammel, R., Ackermann, R., Thomas, J., Götte, J., Skupin, S., Tünnermann, A., and Nolte, S.
• College/School: College of Science and Engineering > School of Physics and Astronomy
• Journal Name: Light: Science and Applications
• Publisher: Nature Publishing Group
• ISSN: 2047-7538
• ISSN (Online): 2047-7538
• Published Online: 09 May 2014
• Copyright Holders: Copyright © 2014 CIOMP
• First Published: First published in Light: Science and Applications 3:e169
• Publisher Policy: Reproduced under a creative commons license