INVESTIGATION OF THE ELEMENTARY PHYSICAL PROCESSES IN PLASMA OF FILAMENTATION AND OPTICAL BREAKDOWN REGIONS ACCOMPANYING THE PROPAGATION OF THE FEMTOSECOND LASER PULSE WITH WAVELENGTH OF 950 nm IN AIR AT ATMOSPHERIC PRESSURE

摘要

For the first time comparative investigations are performed of the emission spectra of pure air breakdown plasma initiated by a high-voltage pulse nanosecond discharge and nanosecond and femtosecond optical pulses. The plasma initiated in air by femtosecond laser pulses differs significantly from the plasma initiated by the nanosecond high-voltage discharge and optical breakdown. The propagation of femtosecond laser radiation in pure nitrogen in the filamentation region is accompanied by stimulated emission on transitions of the molecular nitrogen ion at a wavelength of 427.8 nm. The energy of the laser electromagnetic field is accumulated in the field of charged particles and is mainly dissipated in the processes of dissipative recombination. It is demonstrated that the emission spectra of air in the range 0.6-1 μm coincide almost completely for all excitation types, and in the range 0.2-0.6 μm, these spectra have the characteristic features caused by the parameters of high-voltage and optical breakdown plasma.