Femtosecond reduction of atomic scattering factors triggered by intense x-ray pulse

TL;DR

This study demonstrates that intense femtosecond x-ray pulses can cause a rapid reduction in atomic scattering factors in silicon, leading to suppressed diffraction intensity due to ultrafast atomic ionization.

Contribution

It provides experimental evidence and simulation confirmation of femtosecond-scale atomic scattering factor reduction caused by ultrafast ionization under intense x-ray irradiation.

Findings

Diffraction intensity decreases significantly at high x-ray intensities.

Atomic scattering factors are reduced on femtosecond timescales due to ionization.

Potential for new nonlinear x-ray techniques based on this effect.

Abstract

X-ray diffraction of silicon irradiated with tightly focused femtosecond x-ray pulses (photon energy: 11.5 keV, pulse duration: 6 fs) was measured at various x-ray intensities up to $4.6\times10^{19}$ W/cm$^2$. The measurement reveals that the diffraction intensity is highly suppressed when the x-ray intensity reaches of the order of $10^{19}$ W/cm$^2$. With a dedicated simulation, we confirm the observed reduction of the diffraction intensity is attributed to the femtosecond change in individual atomic scattering factors due to the ultrafast creation of highly ionized atoms through photoionization, Auger decay, and subsequent collisional ionization. We anticipate that this ultrafast reduction of atomic scattering factor will be a basis for new x-ray nonlinear techniques, such as pulse shortening and contrast variation x-ray scattering.