Spectral components of laser radiation arising by the interaction of post-pulses and amplified spontaneous emission with plasma of the femtosecond filaments in air

The dynamics of spectral components arising in the time interval up to 15 ns after the main femtosecond pulse is investigated for filamentation of tightly focused laser radiation. The femtosecond pulse duration was 65 fs, the main pulse energy increased from 0.5 to 1.7 mJ. Several spectral components of laser emission in the wavelength range of 720–780 nm are registered. With increase of main pulse energy, the shape of the spectrum of the supercontinuum changes, the intensity of the post-pulse and the amplified spontaneous emission increases, and a shift of the component to the blue region is observed. It is assumed that the component whose central wavelength shifts to the blue region with is associated with Rabi splitting of the oxygen atom levels.