title: Atomic inner-shell X-ray laser at 1.46 nanometres pumped by an X-ray free-electron laser.
abstract: Since the invention of the laser more than 50 years ago, scientists have striven to achieve amplification on atomic transitions of increasingly shorter wavelength. The introduction of X-ray free-electron lasers makes it possible to pump new atomic X-ray lasers with ultrashort pulse duration, extreme spectral brightness and full temporal coherence. Here we describe the implementation of an X-ray laser in the kiloelectronvolt energy regime, based on atomic population inversion and driven by rapid K-shell photo-ionization using pulses from an X-ray free-electron laser. We established a population inversion of the Kα transition in singly ionized neon at 1.46 nanometres (corresponding to a photon energy of 849 electronvolts) in an elongated plasma column created by irradiation of a gas medium. We observed strong amplified spontaneous emission from the end of the excited plasma. This resulted in femtosecond-duration, high-intensity X-ray pulses of much shorter wavelength and greater brilliance than achieved with previous atomic X-ray lasers. Moreover, this scheme provides greatly increased wavelength stability, monochromaticity and improved temporal coherence by comparison with present-day X-ray free-electron lasers. The atomic X-ray lasers realized here may be useful for high-resolution spectroscopy and nonlinear X-ray studies.
authors.affiliation: Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, California 94551, USA. nina.rohringer@asg.mpg.de
authors.forename: Nina
authors.initials: N
authors.lastname: Rohringer
authors.forename: Duncan
authors.initials: D
authors.lastname: Ryan
authors.forename: Richard A
authors.initials: RA
authors.lastname: London
authors.forename: Michael
authors.initials: M
authors.lastname: Purvis
authors.forename: Felicie
authors.initials: F
authors.lastname: Albert
authors.forename: James
authors.initials: J
authors.lastname: Dunn
authors.forename: John D
authors.initials: JD
authors.lastname: Bozek
authors.forename: Christoph
authors.initials: C
authors.lastname: Bostedt
authors.forename: Alexander
authors.initials: A
authors.lastname: Graf
authors.forename: Randal
authors.initials: R
authors.lastname: Hill
authors.forename: Stefan P
authors.initials: SP
authors.lastname: Hau-Riege
authors.forename: Jorge J
authors.initials: JJ
authors.lastname: Rocca