Abstract
A scheme is put forward to generate fully coherent x-ray lasers based on population inversion in highly charged ions, created by fast inner-shell photoionization using broadband x-ray free-electron-laser (XFEL) pulses in a laser-produced plasma. Numerical simulations based on the Maxwell–Bloch theory show that one can obtain high-intensity, femtosecond x-ray pulses of relative bandwidths Δω/ω = 10−5–10−7, by orders of magnitude narrower than in x-ray free-electron-laser pulses for discrete wavelengths down to the sub-ångström regime. Such x-ray lasers can 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.
Highlights
In order to show how the plasmas discussed in this paper can be produced with current laser facilities, we provide a conservative estimation of the laser conditions necessary to generate, e.g., a plasma consisting of highly charged Ar ions, for lasing from the 3P1 → 1S0
The codes used to generate the results reported in this study are available from the corresponding author upon reasonable request
The XRLs put forward here can be used to perform coherent x-ray pump-probe experiments for investigations of structural relaxation processes[91]
Summary
Maxwell–Bloch theory has been successfully applied to describe the amplification and absorption of light in active media[57], including the development of soft x-ray lasers in laser-produced plasmas[92]. After the experimental realization of XRL pumped by an XFEL pulse, in ref. 59, Weninger and Rohringer successfully applied this theory to model the evolution of the corresponding XRL. We extend this theory to include lasing from multipole transitions, i.e., M1 and M2 transitions. Assuming XFEL pulses www.nature.com/scientificreports propagating along the xdirection, the evolution of the XRL field in the slowly varying envelope approximation is given by. Under the two-level approximation in He-like ions, we assume all Li-like ions are pumped into the corresponding upper lasing state of such transition by the XFEL pulse.
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