Near-Infrared Dual Comb Spectroscopy for Thermal Blooming Prediction

Thermal blooming is a major nonlinear effect for high energy laser (HEL) beams propagating through the atmosphere. Due to this effect, the beam pattern is distorted through the propagation path, thus limiting the maximum power that can be efficiently transmitted through the atmosphere. There is a critical need to accurately predict thermal blooming for military applications.  Although some methods have been suggested for compensating thermal blooming using phase conjugation akin to adaptive optics, there is usually a critical power beyond which the phase conjugation does not lead to increased power on target.  For this effort, we propose using a dual-frequency comb (DFC) system for near infrared absorption spectroscopy to make predictions on thermal blooming in various outdoor/turbulence environments. Due to a fast scan rate, the DFC system will be less immune to turbulence. By putting the DFC system in situ with the HEL, we can in principle measure the absorption prior to engaging the target and predict whether the HEL will be effective or not based on the absorption measurements.