Performance studies of a multilayer-based radiation pulse slicer for Linac Coherent Light Source (LCLS) applications

The SLAC Linac Coherent Light Source (LCLS), an X-ray Free- Electron Laser (XRFEL) designed to operate over a fundamental energy range of 1 - 8.5 keV, is expected to produce ultra-short pulse lengths down to approximately 200 fs. Even though this represents an enormous decrease with respect to currently available high-brightness X-ray sources, it is believed that for a number of proposed LCLS applications (e.g., imaging or structural studies of molecular clusters with highly focused pulses) it will become necessary to reduce the pulse duration even further, possibly by as much as 1-2 orders of magnitude. Of the various compressive or chopping (i.e., slicing) optical techniques considered for shortening the pulse, the focus of one of our recent studies has been on a recently proposed slicing scheme based on the interaction of a longitudinally chirped LCLS pulse with a specially designed multilayer. The chopping mechanism is the selective reflection of only that sub-interval of the pulse that fulfills the multilayer Bragg condition. Of particular interest are the reflection efficiency and the distortion induced in the temporal fine structure of the reflected pulse, both of which can be critical to the efficacy of the scheme for a given application. Here we present results of selected parameter studies of different multilayer-based beam chopper systems using codes and LCLS radiation models developed at SSRL and LLNL.