Revisiting the Critical Physics for Passing Energetic Laser Pulses through Air

Program Overview

This project revised existing models for generated stimulated rotational Raman scattering (SRRS) in the air with measurements for nano-second long pulsed laser beams with a focus on beam break-up and dispersal during propagation. We have constructed a 4-dimensional split-step beam propagation model (x-y-x-t) that contains the known dominant physics components: diffraction, Kerr nonlinearity, turbulence and SRRS. We have included several accepted models from the literature for SRRS, as well as additional code enhancements, e.g., automatically adjusting propagation step size. The newly developed model was validated with available software and experimental work from literature for modest SRRS generation. The in-house code presents speed performance enhancement, additional capabilities with respect to existing codes, as well as the access to be tweaked as needed. We have measured SRRS generation using a table-top setup and folding beam path for distances of up to 50 m with J-class nano-second pulsed laser. Even though we have found that this configuration is experimentally challenging, we have managed to get agreement between the model and the measurement in relatively strong SRRS generation cases. These preliminary measurements and the model suggest that the coupled SRRS and laser beams, while exchanging energy, will typically not break-up and disperse for such beams and propagation. Modes of potential dispersal and mitigations could be further studied by the developed model and setup. Therefore, this new capability and findings could lead to a better understanding of transmission of energetic laser pulses through the air, which in turn could benefit applications of laser including high energy laser designs for inertial confinement fusion (ICF) and other high energy density sciencey (HEDS) science applications.

Mission Impact

The proposed study is strongly aligned with Lasers and Optical Science and Technology. It will enable better understanding of the design, operation, and applications of lasers and laser facilities that produce high energy laser pulses and would clearly enhance its related modeling capability and system engineering.