During the last 20 years much attention has been given to the study of propagation of short intense laser pulses for which the peak power exceeds the critical power of self-focusing, Pcr. For a laser power P < Pcr, a dynamic equilibrium between the Kerr self-focusing, diffraction and defocusing caused by laser-ionized plasma result in the production of a high intensity laser filament in air within which a variety of nonlinear optical phenomena are observed. However, research in the 0.8-1 m range so far has shown a fundamental limitation of guided energy to a few mJ transported within an ~100 m single channel.
A long-wavelength, 0~10 m CO2 laser is a promising candidate for nonlinear guiding because expected high Pcr values according to the modeling should allow for the increase of energy (and therefore power) in a self-guided beam from mJ (GW) to few Joules (TW). During the last decade a significant progress has been achieved in amplification of picosecond pulses to terawatt and recently to <10 TW power level at UCLA and ATF BNL. Such powerful 10 m lasers open possibility for nonlinear propagation studies in an atmospheric window with high transmission. As a natural first step in a our program on picosecond CO2 laser filamentation, we have made first measurements of Kerr coefficients of air and air constituents around 10 m. We also undertook direct measurements of n2 of air by analyzing nonlinear self-focusing in air using a ~3 ps, 600 GW pulses of the BNL CO2 laser.
Sergei Tochitsky, "Nonlinear guiding of picosecond CO2 laser pulses in atmosphere (Conference Presentation)," Proc. SPIE 10193, Ultrafast Bandgap Photonics II, 101930L (Presented at SPIE Defense + Security: April 11, 2017; Published: 7 June 2017); https://doi.org/10.1117/12.2261892.5459357363001.
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