Filamentation of long-wave infrared pulses in the atmosphere [Invited]

Filamentation of a high-power laser beam in air opens the possibility of the diffraction-compensated propagation of a laser beam over long distances and as such is being considered for remote stand-off detection, lightning control, free-space communications, and long-range projection of high-energy pulses. Switching to long-wave infrared (LWIR) range for filamentation, as shown in recent experiments, allows for generation of a single centimeter-diameter channel in air that, in comparison with a short-wavelength laser filament, has 4 orders of magnitude larger cross section and guides many joules of pulse energy over multiple Rayleigh distances at a clamped intensity of ∼10¹² W/cm². Self-guiding of LWIR pulses in air arises from the balance between self-focusing, diffraction, and defocusing caused by free carriers generated via many-body Coulomb-induced ionization which effectively decrease the molecular polarizability during the long-wavelength laser pulse. Understanding where this new ionization regime plays a role, below the threshold of the well-adopted single-atom tunnel ionization in gases, could become a new frontier in strong-field interactions. This paper offers an overview of the atmospheric filamentation research at long-wave infrared wavelengths.