Article | Published:

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.

Access optionsAccess options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

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.


  1. 1.

    Laser Beam Propagation in the Atmosphere (ed. Strohbehn, J. W.) Topics in Applied Physics Vol. 25 (Springer, Berlin, Heidelberg, 1978).

  2. 2.

    Lubin, P. et al. Toward directed energy planetary defense. Opt. Eng. 53, 025103 (2014).

  3. 3.

    Daukantas, P. Breakthrough starshot. Opt. Photon. News 28, 26–33 (2017).

  4. 4.

    Nicholls, R. W. Wavelength-dependent spectral extinction of atmospheric aerosols. Appl. Opt. 23, 1142–1143 (1984).

  5. 5.

    Andrews, L. C. & Phillips, R. L. Laser Beam Propagation through Random Media (SPIE Optical Engineering Press, Bellingham, 1998)

  6. 6.

    Braun, A. et al. Self-channeling of high-peak-power femtosecond laser pulses in air. Opt. Lett. 20, 73–75 (1995).

  7. 7.

    Couairon, A. & Mysyrowicz, A. A femtosecond filamentation in transparent media. Phys. Rep. 44, 47–189 (2007).

  8. 8.

    Chin, S. L. Femtosecond Laser Filamentation Springer Series on Atomic, Optical and Plasma Physics Vol. 55 (Springer, New York, 2010).

  9. 9.

    Mitrofanov, A. V. et al. Mid-infrared laser filaments in the atmosphere. Sci. Rep. 5, 8368 (2015).

  10. 10.

    Shumakova, V. et al. Filamentation of mid-IR pulses in ambient air in the vicinity of molecular resonances. Opt. Lett. 43, 2185–2188 (2018).

  11. 11.

    Mechain, G. et al. Long range self-channeling of infrared laser pulses in air: a new propagation regime without ionization. App. Phys. B 79, 379–382 (2004).

  12. 12.

    Durand, M. et al. Kilometer range filamentation. Opt. Express 21, 26836–26845 (2013).

  13. 13.

    Zhao, X. M., Diels, J.-C., Wang, C. Y. & Elizondo, J. M. Femtosecond ultraviolet laser pulse induced lightning discharges in gases. IEEE J. Quantum. Electron. 31, 599–612 (1995).

  14. 14.

    Kartashov, D. et al. Free-space nitrogen gas laser driven by a femtosecond filament. Phys. Rev. A 86, 033831 (2012).

  15. 15.

    Stelmaszczyk, K. et al. Long-distance remote laser-induced breakdown spectroscopy using filamentation in air. Appl. Phys. Lett. 85, 3977–3979 (2004).

  16. 16.

    Point, G. et al. Superfilamentation in air. Phys. Rev. Lett. 112, 223902 (2014).

  17. 17.

    Chateauneuf, M., Payeur, S., Dubois, J. & Kieffer, J.-C. Microwave guiding in air by a cylindrical filament array waveguide. Appl. Phys. Lett. 92, 091104 (2008).

  18. 18.

    Rohwetter, P. et al. Laser-induced water condensation in air. Nat. Photon. 4, 451–456 (2010).

  19. 19.

    Geints, Y. E. & Zemlyanov, A. A. Single and multiple filamentation of multi-terawatt CO2 laser pulses in air: numerical simulations. J. Opt. Soc. Am. B 31, 788–797 (2014).

  20. 20.

    Panagiotopoulos, P., Schuh, K., Kolesik, M. & Moloney, J. M. Simulations of 10 μm filaments in a realistically modeled atmosphere. J. Opt. Soc. Am. B 33, 2154–2161 (2016).

  21. 21.

    Schuh, K., Kolesik, M., Wright, E. M. & Moloney, J. M. Self-channeling of high-power long-wave infrared pulses in atomic gases. Phys. Rev. Lett. 118, 063901 (2017).

  22. 22.

    Haberberger, D., Tochitsky, S. & Joshi, C. Fifteen terawatt picosecond CO2 laser system. Opt. Express 18, 17865–17877 (2010).

  23. 23.

    Polyanskiy, M. N., Babzien, M. & Pogorelsky, I. V. Chirped-pulse amplification in a CO2 laser. Optica 2, 675–679 (2015).

  24. 24.

    Polyanskiy, M. N., Pogorelsky, I. V. & Yakimenko, V. Picosecond pulse amplification in isotope CO2 active medium. Opt. Express 19, 7717–7725 (2011).

  25. 25.

    Pigeon, J. J., Tochitsky, S. Ya., Welch, E. C. & Joshi, C. Measurements of the nonlinear refractive index of air, N2 and O2 at 10 μm using four-wave mixing. Opt. Lett. 41, 3924–3927 (2016).

  26. 26.

    Tochitsky, S. Ya. et al. Efficient shortening of self-chirped picosecond pulses in a high-power CO2 amplifier. Opt. Lett. 26, 813–815 (1995).

  27. 27.

    Keldysh, L. V. Ionization in the field of a strong electromagnetic wave. Sov. Phys. JETP 20, 1307–1314 (1965).

  28. 28.

    Raiser, Y. P. Gas Discharge Physics (Springer, New York, 1987)..

  29. 29.

    Pigeon, J. J., Tochitsky, S. Ya., Welch, E. C. & Joshi, C. Experimental study of the third-order nonlinearity of atomic and molecular gases using 10-μm laser pulses. Phys. Rev. A 97, 043829 (2018).

  30. 30.

    Geints, Y. E. & Zemlyanov, A. A. Dynamics of CO2 laser filamentation in air influenced by spectrally selective molecular absorption. Appl. Opt. 53, 5641–5648 (2014).

  31. 31.

    Bendtsen, J. The rotational and rotation-vibrational Raman spectra of 14N2, 14N15N, and 15N2. J. Raman Spectrosc. 2, 133–145 (1974).

  32. 32.

    Kira, M. & Koch, S. W. Semiconductor Quantum Optics (Cambridge University Press, Cambridge, 2012).

  33. 33.

    Schuh, K., Moloney, J. M. & Koch, S. W. Influence of many-body interactions during the ionization of gases by short intense optical pulses. Phys. Rev. E 89, 033103 (2014).

  34. 34.

    Kolesik, M. & Moloney, J. V. Nonlinear optical propagation simulation from Maxwell’s to unidirectional equations. Phys. Rev. E 70, 0366604 (2004).

  35. 35.

    Pasenow, B. et al. Nonequilibrium evolution of strong-field anisotropic ionized electrons towards a delayed plasma state. Opt. Express 20, 2310–2318 (2012).

  36. 36.

    Gao, X. et al. Picosecond ionization dynamics in femtosecond filaments at high pressure. Phys. Rev. A 95, 013412 (2017).

  37. 37.

    Rothman, L. S. et al. The HITRAN 2012 molecular spectroscopic database. J. Quant. Spectrosc. Radiat. Transfer 130, 4–50 (2013).

  38. 38.

    Couairon, A. et al. Practitioner’s guide to laser pulse propagation models and simulation. Eur. Phys. J. Spec. Top. 199, 5–76 (2011).

  39. 39.

    Agrawal, G. P. Nonlinear Fiber Optics (Academic Press, USA, 2001).

  40. 40.

    Adair, R., Chase, L. L. & Payne, S. A. Nonlinear refractive index of optical crystals. Phys. Rev. B 39, 3337–3349 (1989).

Download references


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.

Author information

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.

Correspondence to Sergei Tochitsky.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Supplementary information

Supplementary Information

Additional data, analysis and modelling

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Further reading

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.