Nonlinear enhancement of resonance absorption at the filamentation of a mid-infrared pulse in high-pressure gases

It has been found experimentally that the filamentation of a femtosecond pulse with a central wavelength of 1.3 $\mu$m in a mixture of nitrogen at a pressure of 30 bar and water vapor at a pressure of 2 mbar results in the redshift of the spectrum of the pulse and in the corresponding enhancement of resonance absorption at water lines near a wavelength of 1.35 $\mu$m. A replica of the resonance absorption band has been detected in the continuous spectrum of a pulse transmitted through the cell. The characteristic absorption lines of water detected experimentally correspond to the results of the numerical simulation of a three-dimensional nonstationary problem taking into account the resonance and nonresonance absorption in molecular gases.