Filament formation beyond linear focus during femtosecond laser pulse propagation in air

High intensive light channel formation in the post-filamentation region of ultrashort laser pulses in air

“…Air nonlinear optical model includes instant and inertial Kerr effects, high-order nonlinearities (saturation of Kerr nonlinearity), and complex refractive index variations upon air photoionization and free electron gas formation. Linear part of the propagation equation describes pulse group velocity dispersion (GVD) and beam diffraction providing for nonparaxiality of focused beam propagation [26]. Free electron concentration dynamics, r , e was calculated using the kinetic equation accounting for multiphoton/tunnel and avalanche ionization mechanisms of air gas constituents (N 2 , O 2 ).…”

Using the nonlinear layer model for estimation of characteristics of high-power ultrashort laser pulse beams propagating along an aerospace path

“…is the coherence radius of induced inhomogeneities in the nonlinear layer.The formation of these inhomogeneities occurs due to small-scale self-focusing, filamentation, and postfilamentation channeling. In accordance with the results of experiments of the propagation of ultrashort laser pulses in surface layer of the atmosphere[2,16,17], we assume for estimates that * k   (0.01-0.1) m in the nonlinear layer. For a wide laser beam in the region of nonlinearity…”

“…, where n20 is the medium non-linearity coefficient at sea level, z is the propagation distance, h * is the atmospheric inhomogeneity layer (h * =6.8 km according to [2]).…”