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Research group Z. Harman – Division C. H. Keitel
Abstract:
The generation of narrow-band fully coherent x-ray lasers based on stimulated emission
in highly charged ions is investigated. The lasing scheme we put forward leads to x-ray
sources with high spatial and temporal coherence, enabling new applications in x-ray
quantum optics. Highly charged ions can be generated in plasmas created by linefocused
intense optical lasers. Population inversion between the 1s2l (l = s, p) and
1s2 states in He-like ions is obtained by inner-shell photoionization of Li-like ions with
intense x-ray free-electron laser pulses. We show that lasing can happen in elements such
as Ne, Ar, Kr and Xe through E1, M1 or M2 transitions. The corresponding Maxwell–
Bloch equations are developed with the inclusion of multipole interactions between the
x-ray fields and the ions. Numerical simulations show that the x-ray lasers generated
this way are characterized by high intensities and with femtosecond pulse durations.
The relative bandwidths of Δω/ω = 10−5 – 10−7 achieved are by up to 3 orders of
magnitude narrower than in pulses from state-of-art x-ray sources at wavelengths down
to the sub-ångström regime. Analytical solutions of the Maxwell–Bloch equations in
the exponential-gain approximation are found to give results consistent with numerical
simulations for the pulse and spectral profiles.
