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  4. Enhancing precision in fs-laser material processing by simultaneous spatial and temporal focusing
 
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2014
Journal Article
Title

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

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 mJ, 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 mJ, 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.
Author(s)
Kammel, Robert  
Ackermann, Roland
Götte, Jörg
Thomas, Jens
G
Skupin, Stefan
Tünnermann, Andreas  
Nolte, Stefan  
Journal
Light. Online resource  
Open Access
DOI
10.1038/lsa.2014.50
Additional full text version
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Language
English
Fraunhofer-Institut für Angewandte Optik und Feinmechanik IOF  
Keyword(s)
  • filamentation

  • fs-laser surgery

  • laser-induced optical breakdown

  • materials processing

  • plasma shadowgraphy

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