Numerical study of spatial propagation dynamics and energy delivery of TW square-aperture CO₂ laser pulses in the atmosphere

We numerically study the linear and nonlinear spatial propagation dynamics of multi-Joule 10.6 μm square beams in the atmosphere for various square obscuration locations. We show that the spatial reshaping process of these square frame shaped beams, a process normally driven by strong linear diffraction, can be significantly altered in the nonlinear regime. Depending on the input power, linear dynamics can be mostly preserved or overpowered by the optical Kerr effect leading to the formation of single or multi-filament patterns, at propagation distances of a few tens of meters in the atmosphere. Optimal power delivery downstream is dependent on the location of the square obscuration and overall input power. Our results offer significant insight to ongoing efforts of high peak power CO₂ mid-IR lasers generated in unstable resonators for atmospheric applications.