title: Ultrafast Excitation of an Inner-Shell Electron by Laser-Induced Electron Recollision.
abstract: Extreme ultraviolet attosecond pulses, generated by a process known as laser-induced electron recollision, are a key ingredient for attosecond metrology, providing a tool to precisely initiate and probe subfemtosecond dynamics in atoms, molecules, and solids. However, extending attosecond metrology to scrutinize the dynamics of the inner-shell electrons is a challenge, that is because of the lower efficiency in generating the required soft x-ray (ℏω>300  eV) attosecond bursts. A way around this problem is to use the recolliding electron to directly initiate the desired inner-shell process, instead of using the currently low flux x-ray attosecond sources. Such an excitation process occurs in a subfemtosecond time scale, and may provide the necessary "pump" step in a pump-probe experiment. Here we used a few cycle infrared (λ_{0}≈1800  nm) source and observed direct evidence for inner-shell excitations through the laser-induced electron recollision process. It is the first step toward time-resolved core-hole studies in the keV energy range with subfemtosecond time resolution.
authors.affiliation: SwissFEL, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland.
authors.forename: Yunpei
authors.initials: Y
authors.lastname: Deng
authors.affiliation: State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China.|IFSA Collaborative Innovation Center, Shanghai Jiao Tong University, Shanghai 200240, China.
authors.forename: Zhinan
authors.initials: Z
authors.lastname: Zeng
authors.affiliation: State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China.
authors.forename: Zhengmao
authors.initials: Z
authors.lastname: Jia
authors.affiliation: Department of Applied Physics, Benin School of Engineering and Computer Science, Hebrew University of Jerusalem, Jerusalem 91904, Israel.
authors.forename: Pavel
authors.initials: P
authors.lastname: Komm
authors.affiliation: State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China.
authors.forename: Yinhui
authors.initials: Y
authors.lastname: Zheng
authors.affiliation: State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China.
authors.forename: Xiaochun
authors.initials: X
authors.lastname: Ge
authors.affiliation: State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China.|IFSA Collaborative Innovation Center, Shanghai Jiao Tong University, Shanghai 200240, China.|School of Physical Science and Technology, ShanghaiTech University, Shanghai 200031, China.
authors.forename: Ruxin
authors.initials: R
authors.lastname: Li
authors.affiliation: Department of Applied Physics, Benin School of Engineering and Computer Science, Hebrew University of Jerusalem, Jerusalem 91904, Israel.
authors.forename: Gilad
authors.initials: G
authors.lastname: Marcus