title: Observation and theory of X-ray mirages.
abstract: The advent of X-ray lasers allowed the realization of compact coherent soft X-ray sources, thus opening the way to a wide range of applications. Here we report the observation of unexpected concentric rings in the far-field beam profile at the output of a two-stage plasma-based X-ray laser, which can be considered as the first manifestation of a mirage phenomenon in X-rays. We have developed a method of solving the Maxwell-Bloch equations for this problem, and find that the experimentally observed phenomenon is due to the emergence of X-ray mirages in the plasma amplifier, appearing as phase-matched coherent virtual point sources. The obtained results bring a new insight into the physical nature of amplification of X-ray radiation in laser-induced plasma amplifiers and open additional opportunities for X-ray plasma diagnostics and extreme ultraviolet lithography.
authors.affiliation: Faculty of Physics and International Laser Center of M.V. Lomonosov Moscow State University, Moscow, Russia. sergeymagnitskiy@gmail.com
authors.forename: Sergey
authors.initials: S
authors.lastname: Magnitskiy
authors.forename: Nikolay
authors.initials: N
authors.lastname: Nagorskiy
authors.forename: Anatoly
authors.initials: A
authors.lastname: Faenov
authors.forename: Tatiana
authors.initials: T
authors.lastname: Pikuz
authors.forename: Mamoko
authors.initials: M
authors.lastname: Tanaka
authors.forename: Masahiko
authors.initials: M
authors.lastname: Ishino
authors.forename: Masaharu
authors.initials: M
authors.lastname: Nishikino
authors.forename: Yuji
authors.initials: Y
authors.lastname: Fukuda
authors.forename: Masaki
authors.initials: M
authors.lastname: Kando
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Kawachi
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Kato