Shortening X-ray Pulse Duration via Saturable Absorption

TL;DR

This paper demonstrates a nonlinear optical method using core-hole atoms to shorten x-ray pulses by approximately 35%, advancing the potential for nonlinear x-ray optics in the hard x-ray region.

Contribution

It introduces a novel saturable absorption technique utilizing core-hole atoms to effectively reduce x-ray pulse durations.

Findings

Achieved ~35% reduction in x-ray pulse duration.

Validated core-hole atoms as nonlinear optical media for hard x-rays.

Extended nonlinear optical concepts to the hard x-ray regime.

Abstract

To shorten the duration of x-ray pulses, we present a nonlinear optical technique using atoms with core-hole vacancies (core-hole atoms) generated by inner-shell photoionization. The weak Coulomb screening in the core-hole atoms results in decreased absorption at photon energies immediately above the absorption edge. By employing this phenomenon, referred to as saturable absorption, we successfully reduce the duration of x-ray free-electron laser pulses (photon energy: 9.000 keV, duration: 6-7 fs, fluence: 2.0-3.5$\times$10$^5$ J/cm$^2$) by $\sim$35%. This finding that core-hole atoms are applicable to nonlinear x-ray optics is an essential stepping stone for extending nonlinear technologies commonplace at optical wavelengths to the hard x-ray region.