Design and Characteristics of a Population Inversion X-ray Laser Oscillator

TL;DR

This paper presents the design and realization of an X-ray laser oscillator that produces fully coherent, transform-limited 8 keV pulses with high spectral resolution, advancing X-ray laser technology beyond current SASE-based sources.

Contribution

It introduces a novel X-ray laser oscillator using a Bragg cavity and population inversion in a Cu compound, enabling stable, coherent X-ray pulses from 5 to 12 keV.

Findings

Produced intense, fully coherent 8 keV X-ray pulses

Achieved transform-limited pulses with 48 meV spectral resolution

Demonstrated potential extension to other elements and energies

Abstract

Oscillators are at the heart of optical lasers, providing stable transform limited pulses. In contrast, X-ray free electron lasers use self-amplified spontaneous emission (SASE), resulting in large stochastic intensity and spectral fluctuations. Amplified spontaneous emission (ASE) of the $K\alpha_1$ line has been recently observed for Ne gas, Cu compounds and Mn solutions at the LCLS and SACLA X-ray free electron lasers (XFELs), using an X-ray SASE pulse as a pump to create population inversion. Here we describe the physics and realization of an X-ray laser oscillator (XLO) based on periodically pumping a Cu compound gain medium in a tunable Bragg cavity with a SASE pulse train, generating intense ($\sim$ 5 x 10$^{10}$ ph/pulse), fully coherent, transform limited 8 keV pulses with 48 meV spectral resolution. We also discuss extending these results to other elements to operate XLO from about 5 to 12 keV, improving X-ray-based research beyond current capabilities.