Filaments and post-filaments formation during high-power Ti:sapphire laser pulses propagation in air and optical glasses

Abstract

While propagating in air in the filamentation regime a high-power ultrashort laser pulse experiences the self-organizing into spatially localized light channels, which represent parts of laser beam with the highest intensity and have angular divergence reduced in comparison with the beam as a whole. We present the experimental results on the main characteristics of post-filamentation channels formed by the filamentation of Ti:Sapphire-laser pulses (744 nm, 90 fs) in air. We found that these post-filamentation channels are characterized by a number of features, namely, broader spectral composition with pronounced red shift against the initial pulse spectrum, strong nonlinear phase modulation, and reduced pulse duration. We showed that the increase of initial pulse energy from 0.5 to 2 mJ does not affect post-filamentation channel energy (about 0.4 mJ) though leads to significant change in its spectrum. Thereby, relatively high intensity (more than 0.1 TW/cm2), low angular divergence (fractions of mrad) and wide spectral range of post-filamentation channel help to obtain an ultra supercontinual pulse spectrum by means of post-filamentation channel recurrent filamentation in a medium with high optical nonlinearity (e.g., solid dielectric). The obtained results can be useful in solving the practical task of high-intensive post-filamentation light channels application in laser pulse energy long-range delivery.