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Pump-probe investigation of fs-LIOB in water by simultaneous spatial and temporal focusing

: Kammel, Robert; Ackermann, Roland; Tünnermann, Andreas; Nolte, Stefan


Heisterkamp, A. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
Frontiers in Ultrafast Optics: Biomedical, Scientific, and Industrial Applications XIII : 2 - 7 February 2013, San Francisco, California
Bellingham, WA: SPIE, 2013 (Proceedings of SPIE 8611)
ISBN: 978-0-8194-9380-4
Paper 86110A
Conference "Frontiers in Ultrafast Optics - Biomedical, Scientific, and Industrial Applications" <13, 2013, San Francisco/Calif.>
Conference Paper
Fraunhofer IOF ()
simultaneous spatial and temporal focusing; laser-induced optical breakdown; laser tissue interaction; fs-laser surgery; femtosecond laser materials processing; self-focusing

Femtosecond lasers are a versatile tool to process transparent materials like glasses, polymers or ophthalmic tissue. However, when focusing pulses of several µJ into the material, the high intensity near the laser focus leads to undesired nonlinear side effects like self-focusing and filamentation, resulting in an increased length of the induced plasma or the fragmentation of the breakdown volume. To overcome this limitation, we studied the influence of simultaneous spatial and temporal focusing (SSTF) on the laser induced optical breakdown (LIOB) in water. For this purpose, the incoming laser pulse is spectrally separated by a grating stretcher setup and recompressed by the focusing optics. Due to the increased pulse duration outside of the laser focus, the nonlinear laser-material interaction is confined to the focal region. We investigated the formation of the plasma and the resulting disruption in water by shadow imaging. With conventional focusing (T = 70 fs, NA = 0.1) self-focusing, filamentation and breakup of the disruption volume was observed for pulse energies > 2 µJ, leading to a breakdown length of ~ 800 µm at a pulse energy of 8 µJ. With SSTF the axial length of the breakdown is significantly reduced by a factor of ~ 2. Plasma formation and the resulting disruption stay within the focal region. No self-focusing could be observed for pulse energies up to 8 µJ. Therefore, SSTF appears to be a promising tool to induce photodisruptions in transparent materials even with low numerical aperture, e.g. for precise fs-laser surgery within the posterior segment of the eye.