Ultraintense X‐Ray Interactions at the Linac Coherent Light Source

Abstract

IntroductionUltraintense, tunable X-ray pulses recently available from the LCLS, the world's first hard X-ray free electron laser, increase the intensity and fluence available in a single X-ray pulse up to a billion-fold over that typically available at synchrotron facilities. As a result the LCLS has provided a unique opportunity to investigate nonlinear phenomena at short wavelengths. After an introduction to basic X-ray processes, we review initial experiments at the LCLS that establish basic principles of X-ray interactions with matter at intensities approaching 10 18 W/cm 2 at wavelengths down to 0.6 nm. Throughout the chapter interactions with neon atoms are discussed. Neon is taken as a prototypical example as it is a second row element with sufficient complexity to display basic inner-shell processes, Auger decay, radiative relaxation, and shakeup excitation and ionization. The complexity of innershell processes induced in molecules is briefly discussed. Nonresonant processes that selectively address inner-and outer-shell electrons and X-ray-laser-driven resonant processes, such as Rabi flopping of inner-shell electrons, are discussed. The first use of the LCLS for laser-pump/X-ray probe studies of molecular dynamics is discussed. Characterization of LCLS pulse properties, pulse energy, duration, profile, jitter, focus is described, as this knowledge is critical for predictive theoretical models. Finally, an outlook presents prospects for generating a fully coherent X-ray pulse via self-seeding techniques, a matter of considerable impact for atomic physics and imaging experiments.The first laser was built in 1960 by Ted Maiman at Hughes Research Laboratory [1]. It consisted of a flashlamp-pumped 1-cm ruby rod with silvered end faces that exhibited stimulated emission at 6943 Å. Visible lasers and their applications have since become widely appreciated and are commonly found in everyday appliances. However, long-wavelength visible lasers can not be used to fabricate objects at the nanoscale, interrogate matter on the atomic scale, or for high-resolution metrology and microscopy. Envisioning such applications, scientists have long dreamt of producing an X-ray laser. Early proposals dating from the 1960s suggested schemes to Attosecond and XUV Physics, First Edition. Edited by Thomas Schultz and Marc Vrakking.

A versatile pressure-cell design for studying ultrafast molecular-dynamics in supercritical fluids using coherent multi-pulse x-ray scattering

“…For a specific x-ray light source, by reducing d or increasing L , one increases the contrast β . 45 This, however, reduces the scattering intensity I , as shown in Eq. (3) .…”

“…The definition of the speckle contrast and its relation to the ISF in sp-XPCS is 45 where is the contrast of the speckle pattern from the pulse pair at a specific angular wave number Q and a specific relative delay time Δ t of the pulse pair. I tot is the scattering intensity from the pulse pair at a detector pixel with an angular wave number of Q and I tot = I 1 + I 2 , where I 1 and I 2 are scattering intensity contributions of each single pulse in the pulse pair.…”

“…We have assumed a Gaussian spatiotemporal beam profile of the x-ray pulse with x-ray beam parameters specified above to calculate the speckle contrast β following the derivations given in Refs. 45 and 48 .…”