Narrow-band hard-x-ray lasing

TL;DR

This paper proposes a scheme for generating fully coherent, narrow-band x-ray lasers using population inversion in highly charged ions created by XFEL pulses, achieving femtosecond pulses with extremely narrow bandwidths.

Contribution

The authors introduce a novel method to produce highly coherent x-ray lasers with unprecedented spectral purity using population inversion in HCIs induced by XFELs.

Findings

Achieved x-ray pulses with bandwidths of 10^{-5} to 10^{-7}.

Demonstrated potential applications in x-ray quantum optics and high-precision spectroscopy.

Predicted femtosecond, high-intensity x-ray laser pulses at sub-angstrom wavelengths.

Abstract

Since the advent of x-ray free-electron lasers (XFELs), considerable efforts have been devoted to achieve x-ray pulses with better temporal coherence. Here, we put forward a scheme to generate fully coherent x-ray lasers (XRLs) based on population inversion in highly charged ions (HCIs), created by fast inner-shell photoionization using XFEL pulses in a laser-produced plasma. Numerical simulations show that one can obtain high-intensity, femtosecond x-ray pulses of relative bandwidths $\Delta\omega/\omega=10^{-5}$ - $10^{-7}$ by orders of magnitude narrower than in XFEL pulses for wavelengths down to the sub-\aa{}ngstr\"om regime. Such XRLs may be applicable in the study of x-ray quantum optics and metrology, investigating nonlinear interactions between x-rays and matter, or in high-precision spectroscopy studies in laboratory astrophysics.