Filamentation of chirped femtosecond radiation in compressed nitrogen: Spectral saturation effect as a universal manifestation of Kerr collapse arrest in dense gas

The formation of the supercontinuum spectrum during filamentation in compressed nitrogen with chirped femtosecond optical pulses in the sharp focusing regime has been investigated experimentally and theoretically. We show that chirped pulses exhibit a decrease in the spectral broadening of the pulse with increasing gas pressure. At the same time, pulses with a negative chirp demonstrate a wider supercontinuum than pulses equal in modulation depth but positive in chirp sign. A theoretical analysis and numerical modeling of the propagation of high-power chirped femtosecond optical pulses under conditions corresponding to the experiment are carried out, and an adequate analytical model explaining the main features of the formation of spectral characteristics of chirped optical radiation in a compressed gas is elaborated.