Femtosecond X-rays from relativistic electrons: new tools for probing structural dynamics

Abstract

Femtosecond x-ray science is a new frontier in ultrafast research in which time-resolved measurement techniques are applied with x-ray pulses to investigate structural dynamics at the atomic scale on the fundamental time scale of an atomic vibrational period (~100 fs). This new research area depends critically on the development of suitable femtosecond x-ray sources with the appropriate flux (ph/sec/0.1% BW), brightness (ph/sec/mm 2 /mrad 2 /0.1% BW), and tunability for demanding optical/x-ray pump probe experiments. In this paper we review recently demonstrated techniques for generating femtosecond x-rays via interaction between femtosecond laser pulses and relativistic electron beams. We give an overview of a novel femtosecond x-ray source that is proposed based on a linear accelerator combined with x-ray pulse compression.

Ultrafast X-ray Absorption Spectroscopy

“…This necessitates the continued production of fresh time-sliced pulses with the femtosecond laser. Schoenlein and his group pioneered this scheme at a bend magnet beamline of the Advanced Light Source in Berkeley for a repetition rate of 1 kHz. − While this scheme does deliver ultrashort pulses, its disadvantage is that it discards most of the electrons in the original electron bunch and, as a result, the femtosecond X-ray beam it produces is only a thousandth of a typical SR pulse. Furthermore, its extraction from the large pedestal due to the picosecond X-ray pulse is still problematic.…”

Design and validation of an accelerator for an ultracold electron source

“…Here, the electrons are emitted from a submicron surface and are able to produce a current of up to 1 A. Some applications, as, for example, ultrafast electron diffraction [6], x-ray free-electron lasers [7], or x-ray production by Compton scattering [8], can also benefit from higher brightness, but require much larger currents than CNTs can provide. In fact, the required currents can only be produced in pulsed mode.…”

Femtosecond electron diffraction: Direct probe of ultrafast structural dynamics in metal films

“…The importance of these research activities is underlined by the fact that structural changes in materials govern many fundamental processes in nature, such as phase transitions, surface dynamics, and chemical and biological reactions. Although these processes span a broad temporal range of milliseconds to hundreds of femtoseconds, ultimately all of them are driven by the motions of atoms on the time scale of a single vibrational period of 1 picosecond or less (Schoenlein et al, 2001;Sundström, 1996;Zewail, 2000). A real-time and atomiclevel view of these dynamics holds the potential to fully reveal the physical mechanisms and the structurefunction correlations that would otherwise be impossible to extract.…”