Nonparaxial solitons in air

Abstract

Abstract In the present work the soliton regime of propagation in air of ultra-short long-wavelength infrared laser pulses is investigated. The dispersion of atmospheric air in mid-infrared and long-wavelength infrared shows anomalous group velocity dispersion regions for wavelengths in the ranges of 3.5 to 4.2μm and 9.3 to 13.5μm. In these spectral regions the atmospheric air is transparent. From other hand, the nonparaxiality leads to waveguiding regime of propagation for femtosecond pulses with shape of light disks (the transverse size is much bigger than the longitudinal one). It allows reducing this 3D + 1 task to 1D + 1 problem in the same manner as in optical fibers. The combination between anomalous group velocity dispersion and atmospheric nonlinearity is a base for the observation of optical solitons in the air transparency regions for the indicated wavelengths. The main equation in our research is the 1D + 1 nonlinear nonparaxial amplitude equation, written in Galilean and Laboratory coordinate systems. New analytical solution in the form of bright soliton is found. The critical power, needed for the observation of these solitons is of two orders of magnitudes less than the critical one for self-focusing. That is why there are no conditions for ionization of the media.