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K: Kurzzeitphysik
K 3: Laser beam - matter interaction
K 3.2: Vortrag
Donnerstag, 20. März 2003, 11:45–12:00, F04
Ionization of dielectrics by femtosecond laser pulses — •V.V. Temnov1, K. Sokolowski-Tinten1, P. Zhou1, B. Rethfeld1, V.E. Gruzdev2, D. von der Linde1, O.M. Fedotova2, T.V. Smirnova1, and O.K. Khasanov2 — 1Institute for Laser and Plasma Physics, University of Essen, 45117 Essen, Germany — 2Institute of Solid State and Semiconductor Physics NASB, P. Brovka str.17, Minsk 220072, Belarus
To directly study the ionization dynamics in dielectrics we have developed a setup for femtosecond time-resolved imaging Mach-Zehnder interferometry. A strong pump-pulse (Ti:Sa, 800 nm, 40 fs) excites the sample whereas a co-propagating weak time-delayed probe pulse (400 nm, 60 fs) experiences the changes of the refractive index induced by the pump pulse. The changes in the amplitude and phase of the probe pulses due to excitation of the sample are reconstructed from the interferograms by the application of a 2D-Fourier-transform technique. We have applied this technique to study the dynamics of fs-laser excited fused silica. At zero delay-time pump and probe pulses overlap in time leading to a positive phase shift due to cross-phase modulation (optical Kerr effect). At positive delay-times the probe pulses experience negative phase shifts and strong absorption indicating the generation of an electron gas by the pump pulse. The electron gas exhibits a very short life-time of about 100 fs. The experimental results are compared with the numerical simulation of ultrashort pulse propagation that takes into account self-focusing, dispersion and known ionization mechanisms.