X-ray lasing in the keV range

A new method to generate ultra-short x-ray laser pulses, lying on a laser-driven betatron source of photo-pump inner-shell transitions, was proposed. ISPI has been the subject of several theoretical and numerical studies since its “discovery” in 1967 but no experimental demonstration has been achieved yet.
The betatron spectrum and ion population kinetics were modeled and the temporal evolution of the gain coefficient for Kα transitions was assessed. Using measured values of divergence, duration and number of photons per pulse of the LOA betatron source as input parameters, local gain values close to 60 cm^-1 were calculated for nitrogen at 3.2 nm. Significant gain values were also numerically obtained at shorter wavelengths (for neon at 1.5 nm) for a numerically optimized betatron energy distribution. Radiative transfer calculations coupled with this kinetics modeling allowed investigating the amplification behavior of the lasing transitions. It was demonstrated that saturation may be experimentally achieved by using electron bunches accelerated by a 10PW-class laser, as APOLLON in the near future.

Temporal evolution of the local gain coefficient in nitrogen (at a density of 5 10²⁰ cm^-3) for various durations of the LOA betatron pump source (left) and (left) acceleration length and laser power required to reach saturation in a 2mm long gas jet.

Relevant publications

- M. Ribière et al., Appl. Phys. B 101, 753 (2010)
- M. Ribière et al., Appl. Phys. B 106, 809 (2010)