Consequences of Negative Higher-Order Kerr Effect on Laser Filamentation

Date Mo, 06.12.2010 - Mo, 06.12.2010
Time 16:45h
Speaker Prof. Dr. Jean-Pierre Wolf, GAP-Biophotonics, Uni Geneva
Location ETHZ, Hönggerberg Campus, HPF G-6
Program Laser filamentation by numerical simulations

Filaments are generally considered to stem from a dynamic balance between Kerr focusing and defocusing by the plasma generated at the non-linear focus. Based on the recent experimental measurement of the higher-order Kerr indices n4 through n10 in N2, O2 and Ar, we investigated their influence on laser filamentation by numerical simulations. We show that their values are sufficient to provide the dominant contribution to the defocusing terms in self-channeling. However, when varying the wavelength, the respective values of the higher-order non-linear indices and ionization rates vary. We show that the contribution of plasma is weak over the whole visible and near-infrared spectrum, especially for short pulses. On the other hand, in the ultraviolet where ionization rates are higher, as well as for pulses of a few hundreds of femtoseconds or more where the plasma has time to accumulate, defocusing due to the plasma cannot be neglected. Our results renew the vision of filamentation. While the high-intensities at play in the filaments indeed ionize the propagation medium, the plasma is, over most of the spectrum, a by-product rather than a key ingredient of the filamentation process.
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