First realization of an inner-shell atomic x-ray laser in the keV photone-energy regime

January 31, 2012

Since the invention of the laser fifty years ago, laser amplification of atomic transitions have been extended to increasingly high power and shorter wavelength. The photo-ionization based inner‐shell x‐ray lasing scheme was first proposed in 1967 (M. A. Duguay and G. P. Rentzepis), but due to the requirement of an extremely fast and intense x‐ray pump, could never be realized so far. Recently, we successfully demonstrated this lasing scheme at the Linac Coherent Light Source (LCLS) at SLAC. By focusing LCLS x‐ray pulses into a neon gas sample, a long narrow plasma column is produced on femtosecond time scale, by photoionization of a K‐shell electron. Thereby, a population inversion of the 2p‐1s transition (850 eV) in singly ionized neon is established, lasting for only a few femtoseconds due to the subsequent Auger decay of the created core hole. Fluorescence photons, emitted at the front‐end of the plasma column, get amplified by stimulated emission, resulting in ultra bright, femtosecond x‐ray pulses at 850 eV photon energy at the exit of the plasma column.

N. Rohringer et al., Atomic inner-shell x-ray laser at 1.46 nm pumped by an x-ray free electron laser, Nature 481, 488 (2012).