In inertial confinement (ICF) experiments at the NIKE laser facility, the high-power krypton fluoride (KrF) laser output beams propagate through long ($\sim 75\mathrm{m}$) air paths to achieve angular multiplexing, which is required because the KrF medium does not store energy for a sufficiently long time. Recent experiments and simulations have shown that, via stimulated rotational Raman scattering, this propagation can spectrally broaden the laser beam well beyond the $\sim 1$ THz laser linewidth normally achieved by the induced spatial incoherence (ISI) technique used in NIKE. These enhanced bandwidths may be enough to suppress the laser-plasma instabilities which limit the maximum intensity that can be incident on the ICF target. In this paper we investigate an alternative technique that achieves spectral broadening by self-phase modulation in Xe gas, which has a large, negative nonlinear refractive index $\sim 248$ nm, and thus completely avoids transverse filamentation issues. The collective, nonlinear atomic response to the chaotic, nonsteady state ISI light is modeled using a two-photon vector model, and the effect of near-resonant behavior on the spectral broadening is studied.

• Received 25 April 2019

DOI:https://doi.org/10.1103/PhysRevA.100.023831