Plasma-assisted light bullets and wavelength scaling of laser filamentation in the long-wavelength infrared

We model laser filamentation in ZnSe in the mid-infrared (Mid-IR, wavelengths λ = 4 and 6 µm) and the long-wavelength infrared (LWIR, λ = 8 and 10 µm) using carrier-resolved unidirectional pulse propagation equations (UPPE) [1]. We predict an unprecedented propagation regime at λ = 8 µm that supports light bullets [2], which are spatio-temporally non-spreading electromagnetic pulses. Furthermore, in contrast to the previous report in air in the mid-IR [3], we predict that LWIR light bullets in solids critically rely on plasma-mediated dispersion, which dynamically evolves during multiphoton and tunneling ionization as peak plasma densities reach ρ ∼ 6.6 x 10¹⁸ cm^-3. Finally, the plasma-assisted light bullets propagate with sub-cycle pulse durations and peak intensities I ∼ 1.1 x 10¹² W/cm², making them useful for high-harmonic generation and attosecond pulse generation. [1] M. Kolesik and J. V. Moloney, Phys. Rev. E 70, 036604 (2004). [2] Y. Silberberg, Opt. Lett. 15, 1282 (1990). [3] P. Panagiotopoulos, P. Whalen, M. Kolesik, and J. V. Moloney, Nat. Photon. 9, 543 (2015).