Range of multiple filamentation of a terawatt-power large-aperture KrF laser beam in atmospheric air

The range of multiple low-ionized filaments, either stochastically distributed or regularly arranged, produced in atmospheric air by terawatt-power picosecond pulses of a KrF laser was investigated for a nearly collimated beam of 60 mm in diameter. Filamentation patterns, energy attenuation, and spectra evolution were monitored along a 100 m pass in the laboratory air. Resonance-enhanced multiphoton (2 + 1) ionization of water vapor naturally contained in the atmosphere and stimulated rotational Raman scattering in nitrogen are identified as the main features of the filamentation mechanism, while a self-induced loss of laser radiation coherence is the main factor limiting a multiple-filamentation range. (C) 2019 Optical Society of America