Even harder X-rays

Abstract

With the laser just over half a century old, another dream of the pioneers of this light source has been fulfilled. An atomic X-ray laser with unprecedentedly high photon energy has been demonstrated. See Letter p.488 Achieving lasing at increasingly shorter wavelengths is a long-standing goal. This paper demonstrates an X-ray laser operating on an inner-shell transition in singly ionized neon — the first atomic laser in the 1 kiloelectronvolt regime. It is pumped by X-ray free electron laser (XFEL) pulses from the Linac Coherent Light Source at the SLAC National Accelerator Laboratory in Menlo Park, California. The atomic laser's high-intensity, femtosecond X-ray pulse emission has significantly improved wavelength stability, monochromaticity and temporal coherence compared with XFEL radiation. Atomic X-ray lasers could have applications in high-resolution X-ray spectroscopy and nonlinear X-ray studies.