Mid-infrared laser filaments in the atmosphere

TLDR

Filamentation of ultrashort laser pulses in air enables long‑range high‑power transmission and standoff sensing, but the critical power for self‑focusing scales with the square of the wavelength, so longer wavelengths promise much higher peak powers, a goal limited by available sources to the near‑infrared and visible over the past two decades. This work demonstrates, for the first time, atmospheric filamentation of ultrashort mid‑infrared pulses. Using a 3.9‑μm femtosecond laser, the authors exploit the λ² scaling of critical power to generate a single filament with peak powers exceeding 200 GW and energies above 20 mJ. The resulting mid‑infrared filament produces a powerful supercontinuum and unusual harmonic generation, yielding a broadband spectrum from the visible to the mid‑infrared.

Abstract

Abstract Filamentation of ultrashort laser pulses in the atmosphere offers unique opportunities for long-range transmission of high-power laser radiation and standoff detection. With the critical power of self-focusing scaling as the laser wavelength squared, the quest for longer-wavelength drivers, which would radically increase the peak power and, hence, the laser energy in a single filament, has been ongoing over two decades, during which time the available laser sources limited filamentation experiments in the atmosphere to the near-infrared and visible ranges. Here, we demonstrate filamentation of ultrashort mid-infrared pulses in the atmosphere for the first time. We show that, with the spectrum of a femtosecond laser driver centered at 3.9 μm, right at the edge of the atmospheric transmission window, radiation energies above 20 mJ and peak powers in excess of 200 GW can be transmitted through the atmosphere in a single filament. Our studies reveal unique properties of mid-infrared filaments, where the generation of powerful mid-infrared supercontinuum is accompanied by unusual scenarios of optical harmonic generation, giving rise to remarkably broad radiation spectra, stretching from the visible to the mid-infrared.