Techniques To Reduce Thermal Blooming Of Pulsed Lasers

This paper discusses the reduction of thermal blooming in pulsed laser beams. Pulsed lasers are of interest because under many conditions they suffer less blooming degradation than cw systems owing to partial clear out of atmospheric density perturbations between pulses. Unfortunately, scenarios do exist where the pulsed laser system remains limited by thermal blooming. Therefore, techniques to counteract the blooming of pulsed beams merit investigation. Thermal distortion effects in pulsed beams are typically classified in two categories: single-pulse blooming (transient degradation) and multiple-pulse blooming (steady-state degradation). The different perturbing phenomena exhibit dramatically different time scales, a fact which impacts on the selection of correction techniques. Potential enhancement techniques for alleviating pulsed thermal distortion include basic parameter optimization; correction by a transmitter with adaptive phase compensation; and beam guiding by active, remote control of atmospheric density gradients with auxiliary beams. UTRC is investigating the capabilities of several compensation approaches. The results of laboratory scale experiments will be presented demonstrating improved system performance from open-loop and closed-loop phase compensation with adaptive optics and intensity enhancement with beam guiding. Finally, the experimental results will be compared with theoretical code calculations.