Atomic inner-shell radiation seeded free-electron lasers

Abstract

In order to effectively improve the output quality of x-ray free electron laser (XFEL), we theoretically propose an XFEL scheme seeded by atomic inner-shell laser. Atomic inner-shell lasers based on neutral atoms and pumped by XFEL have been experimentally demonstrated [Rohringer et al., Nature (London) 481, 488 (2012), Yoneda et al., Nature (London) 524, 446 (2015)], which produced sub-femtosecond X-ray pulses with increased temporal coherence. It shows that, by using the inner-shell laser as a seed to modulate the electron bunch, very stable and almost fully-coherent short-wavelength XFEL pulses can be generated. The proposed scheme holds promising prospects in x-ray wavelengths, and even shorter.

Recent progress in angle-resolved photoemission spectroscopy

“…It is the most straightforward and cost-effective method to generate FEL radiation, but it can suffer from shot-to-shot intensity and photon-energy fluctuations, longitudinal coherence limits, broad bandwidth, and instability of the output [198]. For the self-seeded mode [199][200][201], as shown in figure 3(b), it typically consists of three sections: the first section is a short undulator to generate a low-energy SASE FEL pulse as a seed for later FEL generation, the second section is a monochromator to reduce the pulse bandwidth [202][203][204][205] and a chicane to delay the electron beam and destroy the micro-bunching formed in the prior SASE process, and the third section is an FEL amplifier to increase power. This method can improve spectral brightness by an order of magnitude compared to SASE FEL and effectively reduce the bandwidth, but it will suffer from low seed power and large fluctuations due to the SASE process.…”

Features and futures of X-ray free-electron lasers

“…For the same setup, if the monochromator is replaced by an atomic gas, the inner-shell laser pumped by an upstream XFEL pulse can be used as the monochromatic seed for a downstream undulator that generates fully coherent XFEL pulses. 46 …”