title: Two-colour hard X-ray free-electron laser with wide tunability.
abstract: Ultrabrilliant, femtosecond X-ray pulses from X-ray free-electron lasers (XFELs) have promoted the investigation of exotic interactions between intense X-rays and matters, and the observation of minute targets with high spatio-temporal resolution. Although a single X-ray beam has been utilized for these experiments, the use of multiple beams with flexible and optimum beam parameters should drastically enhance the capability and potentiality of XFELs. Here we show a new light source of a two-colour double-pulse (TCDP) XFEL in hard X-rays using variable-gap undulators, which realizes a large and flexible wavelength separation of more than 30% with an ultraprecisely controlled time interval in the attosecond regime. Together with sub-10-fs pulse duration and multi-gigawatt peak powers, the TCDP scheme enables us to elucidate X-ray-induced ultrafast transitions of electronic states and structures, which will significantly contribute to the advancement of ultrafast chemistry, plasma and astronomical physics, and quantum X-ray optics.
authors.affiliation: RIKEN SPring-8 Center, Kouto 1-1-1, Sayo, Hyogo 679-5148, Japan.
authors.forename: Toru
authors.initials: T
authors.lastname: Hara
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Inubushi
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Katayama
authors.forename: Takahiro
authors.initials: T
authors.lastname: Sato
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Tanaka
authors.forename: Takashi
authors.initials: T
authors.lastname: Tanaka
authors.forename: Tadashi
authors.initials: T
authors.lastname: Togashi
authors.forename: Kazuaki
authors.initials: K
authors.lastname: Togawa
authors.forename: Kensuke
authors.initials: K
authors.lastname: Tono
authors.forename: Makina
authors.initials: M
authors.lastname: Yabashi
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Ishikawa
mesh_terms: D003116:Color; D004867:Equipment Design; D007834:Lasers; D013997:Time Factors; D014965:X-Rays