Effect of atmospheric turbulence in long-wave infrared (LWIR) filamentation

Atmospheric turbulence plays an important role in long-range propagation of light pulses. Mid-infrared pulses can propagate in air upto hundreds of meters by forming long channels of plasma due to lower ionization losses compared to near-IR pulses. Such long filamentation channels are useful in atmospheric sensing, remote laser-induced breakdown spectroscopy (LIBS), steering and triggering of electric discharges and other long-range applications. We study the effects of atmospheric turbulence in long-wavelength infrared (LWIR) femtosecond filamentation in air. We numerically investigate the combined effects of turbulence and nonlinearity in the long-range propagation of LWIR pulses at 6 μm. We model the nonlinear response of the atmosphere by including Kerr effect, multiphoton-ionization and rotational Raman effects in air the dispersive response of several atmospheric gas species such as N2, O2, Ar, CO2 CH4 and H2O. We model the turbulence using a phase-screen model. The inhomogeneous medium is represented by a series of phase screens located at regular intervals along the propagation direction. This provides an understanding of the robustness of long range filamentation and propagation of LWIR pulses over turbulent medium which essential for several long range applications including free-space optical communication.