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Megafilament in air formed by self-guided terawatt long-wavelength infrared laser


The diffraction-compensated propagation of high-power laser beams in air could open up new opportunities for atmospheric applications such as remote stand-off detection, long-range projection of high-energy laser pulses and free-space communications. Here, we experimentally demonstrate that a self-guided terawatt picosecond CO2 laser beam forms in air a single centimetre-scale-diameter megafilament that, in comparison with a short-wavelength laser filament, has four orders of magnitude larger cross-section and guides many joules of pulse energy over multiple Rayleigh distances at a clamped intensity of ~1012 W cm–2. We discover that this megafilament arises from the balance between self-focusing, diffraction and defocusing caused by free carriers generated via many-body Coulomb-induced ionization that effectively decrease the molecular polarizability during the long-wavelength laser pulse. Modelling reveals that this guiding scheme may enable transport of high-power picosecond infrared pulses over many kilometres in the 8–14 μm atmospheric transmission window.

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Fig. 1: Experimental set-up.
Fig. 2: Self-guiding of a picosecond CO2 laser in air.
Fig. 3: Temporal evolution of a picosecond CO2 laser pulse self-guided in air.
Fig. 4: Spectral measurements of a picosecond CO2 laser pulse self-guided in air.
Fig. 5: Simulation results of a CO2 laser pulse self-guiding in air.
Fig. 6: A few-kilometre-long propagation of a picosecond 10.2 μm pulse in the atmosphere.

Data availability

The data that supports the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.


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The authors would like acknowledge ATF BNL staff for technical support. S.T. would like to thank Y. Geints (Institute of Atmospheric Optics, Tomsk, Russia) for fruitful discussions of CO2 laser filamentation in the atmosphere. This material is based on work supported by the Air Force Office of Scientific Research under award nos. FA9550-16-1-0139 DEF, FA9550-16-1-0088, FA9550-15-1-0272, Office of Naval Research Multidisciplinary University Research Initiative (MURI) grant no. N00014-17-1-2705, and Department of Energy grant DE-SC0010064.

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S.T., E.W. and C.J. conceived and designed the experiments. S.T., E.W., M.P. and I.P. carried out the experiments, S.T., E.W., J.P. and C.J. analysed the data, contributed analysis tools and wrote the paper. P.P., M.K., E.M.W., S.W.K. and J.V.M. carried out numerical simulations, developed theory and wrote the paper.

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Correspondence to Sergei Tochitsky.

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Tochitsky, S., Welch, E., Polyanskiy, M. et al. Megafilament in air formed by self-guided terawatt long-wavelength infrared laser. Nature Photon 13, 41–46 (2019).

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