Attosecond Inner-Shell Lasing at Angstrom Wavelengths

TL;DR

This paper demonstrates that high-intensity XFELs can produce attosecond, angstrom-wavelength X-ray lasing with complex spatial and spectral features, opening new possibilities for quantum X-ray optics.

Contribution

It reveals the occurrence of strong inner-shell X-ray lasing and superfluorescence at angstrom wavelengths driven by XFELs, with detailed analysis of spatial and spectral inhomogeneities.

Findings

X-ray filamentation causes spatial inhomogeneities.

Spectral splitting and broadening driven by Rabi cycling.

Pulse lengths can be less than 100 attoseconds.

Abstract

Since the invention of the laser nonlinear effects such as filamentation, Rabi-cycling and collective emission have been explored in the optical regime leading to a wide range of scientific and industrial applications. X-ray free electron lasers (XFELs) have led to the extension of many optical techniques to X-rays for their advantages of angstrom scale spatial resolution and elemental specificity. One such example is XFEL driven population inversion of 1s core hole states resulting in inner-shell K${\alpha}$ (2p to 1s) X-ray lasing in elements ranging from neon to copper, which has been utilized for nonlinear spectroscopy and development of next generation X-ray laser sources. Here we show that strong lasing effects, similar to those observed in the optical regime, can occur at 1.5 to 2.1 angstrom wavelengths during high intensity (> ${10^{19}}$ W/cm${^{2}}$) XFEL driven inner-shell lasing and superfluorescence of copper and manganese. Depending on the temporal substructure of the XFEL pump pulses(containing ${~10^{6}}$ - ${10^{8}}$ photons) i, the resulting inner-shell X-ray laser pulses can exhibit strong spatial inhomogeneities as well as spectral splitting, inhomogeneities and broadening. Through 3D Maxwell Bloch theory we show that the observed spatial inhomogeneities result from X-ray filamentation, and that the spectral splitting and broadening is driven by Rabi cycling with sub-femtosecond periods. Our simulations indicate that these X-ray pulses can have pulse lengths of less than 100 attoseconds and coherence properties that open the door for quantum X-ray optics applications.