Comparing the Gain of the Ne K-α Inner-Shell X-Ray Laser Using the XFEL to Drive the Kinetics with Photo-Ionization Versus Photo-Excitation

Abstract

Over the last four decades many photo-pumped X-ray laser schemes have been proposed. However, demonstrating these schemes in the laboratory has proved to be elusive because of the difficulty of finding a strong resonant pump line or X-ray source. With the advent of the X-ray free electron laser (XFEL) at the SLAC Linac Coherent Light Source (LCLS) we now have a tunable X-ray laser source that can be used to replace the pump line or X-ray source in previously proposed laser schemes and allow researchers to study the physics and feasibility of photo-pumped laser schemes. Many of these photo-pumped schemes are driven by photo-excitation from a resonant line source but others are driven by photo-ionization from a strong non-resonant X-ray source. Three years ago an inner-shell X-ray laser was demonstrated at 849 eV (1.46 nm) in singly ionized neon gas using the XFEL at 960 eV to photo-ionize the 1s electron in neutral neon followed by lasing on the 2p—1s transition in singly-ionized neon. In this paper we model the neon inner shell X-ray laser under similar conditions to those used at LCLS. We investigate how we can improve the efficiency of the neon laser and reduce the drive requirements by tuning the XFEL to the 1s-3p transition in neutral neon in order to create gain on the 2p-1s line in neutral neon. We explore the sensitivity to the drive intensity, pulse duration, and line-width of the XFEL to better understand how to optimize this inner shell laser by understanding the trade-offs between using photo-ionization versus photo-excitation to drive gain in these systems. We also discuss how photo-ionization of L-shell electrons can be used to create lasing on n = 3 − 2 transitions in materials such as Ar and Cu.