Propagation-induced x-ray phenomena at ultrahigh intensities

Our understanding of x-ray interactions with single isolated particles in the ultraintense multiphoton regime has matured greatly over the past decade as focused, tunable x-ray pulses with intensities up to 10²⁰ W/cm² at wavelengths of 1 Å have become available at x-ray free-electron lasers (XFELs).  A general framework has been developed for ultraintense x-ray interactions with atoms, molecules, clusters and biomolecules – both under resonant and non-resonant conditions.  Much less studied are propagation-based phenomena at high x-ray intensities, where the target-field interaction reshapes the electromagnetic field in the spectral, temporal and spatial domains.  Following the seminal demonstrations of XFEL-pumped atomic lasers and stimulated Raman scattering there have been few investigations in gas-phase systems where theoretical studies are most tractable.  In this talk I will discuss our theoretical study that uses a coupled time-dependent Schroedinger equation/Maxwell wave equation (TDSE/MWE) approach to study propagation in gases [1] and our recent [2] and planned experimental investigations aimed at observing self-induced transparency, stimulated Raman scattering, and four-wave mixing with x-rays.