Synchrotron radiation optics in the short-pulse limit: design implications for the SLAC Linac Coherent Light Source (LCLS)

Abstract

In recent years, a number of studies have been conducted on the source properties of linac-driven X-Ray Free-Electron Lasers (XRFELs) operating in the Self-Amplified Spontaneous Emission (SASE) regime. In longitudinal phase space the output of such devices typically consists of a randomly-distributed train of fully-transversely-coherent micropulses of randomly varying intensity and an average length (corresponding to the coherence length) two to three orders of magnitude smaller than the transverse diameter of the beam. Total pulse lengths are typically of the same order of size as the beam diameter. Both of these properties can be shown to significantly impact the performance of otherwise conventional synchrotron radiation optics (viz., mirrors, lenses, zone plates, crystals, multilayers, etc.) designed to filter or modulate the phase space parameters of the radiation pulses. This, in turn, can influence the design and performance of beam line instrumentation (viz., monochromators, spectrometers, etc.) employed to match the phase space acceptance of an experiment to an XRFEL source. In this paper we outline a preliminary investigation of short-pulse effects on the performance and design of selected optical components and instrumentation for the proposed 1.5 Angstrom SLAC Linac Coherent Light Source (LCLS) and discuss the implication of our results for critical applications such as microfocusing and monochromatization.