Self-action of tightly focused femtosecond laser radiation in air in a filamentation regime: Laboratory and numerical experiments

Post-focal filamentation of an externally focused femtosecond laser pulse in air

“…Regarding the model of Kerr nonlinearity of air, there are still heated debates in the scientific community about the role of the HOKE in laser pulse transverse collapse stopping since it seems to be insignificant compared to radiation defocusing by the induced plasma (see, for example, [13]). According to our experimental data [14] as well as the data in [15], the higher-order Kerr effects should be retained even under conditions of strong plasma formation in the simulation of filamentation of rather short laser pulses (up to hundreds of femtoseconds). Therefore, in the following calculations we will use the full Kerr + HOKE model of air optical nonlinearity.…”

Features of focused propagation of intense femtosecond laser pulses in air under low pressure

“…This assumption is valid at a small excess of the pulse power over the critical power of self focusing and suf ficiently strong initial focusing of the beam [10,11]. The peak of the pulse energy density w m is expressed in terms of its power, supposing also that the temporal profile of the pulse is unchanged and there are no energy losses during propagation to the focus: (2) where the parameter b designates the integral of tem poral form of the pulse (non Gaussian, in the general case).…”