Many atmospheric applications such as free-space communication or spectroscopy require targeted delivery of high-energy ultrashort pulses with a good beam quality. Often atmospheric turbulences complicate this task, causing random variations of the refractive index and resulting in fluctuations of light intensity on the target. Propagation of light in filamentation regime, when intensity is clamped, to a certain extent helps to overtake this problem, but brings ionization-related problems, such as energy loss, temporal pulse splitting, etc. Moreover, maximum peak power , which can be delivered in a single filament is limited to about ten critical powers of self-focusing , after which multiple filamentation and hence small-scale beam distortions take place. In the case of Ti:Sapphire drivers delivering 40-fs, 800-nm pulses, the energy in a single filament in air doesn’t exceed 1 mJ, unless special conditions are applied . However, since ~2 ( is the driver wavelength), essentially more energy can be deposited in a single filament driven by 3.9-μm pulses . Furthermore, mid-IR spectral range is beneficial in virtue of lower ionization rates and higher resistance to modulation instabilities and scattering by natural atmospheric obstacles, such as water droplets . Finally, a unique combination of high atmospheric transparency and anomalous dispersion of air between 3.6-4.2 µm promote an opportunity for a lossless high-energy ultrashort pulse delivery and simultaneous solitonic self-compression .
© 2019 IEEEPDF Article