Ultrashort Optical Pulses in the Linac Coherent Light Source

The Linac Coherent Light Source (LCLS) project at the Stanford Linear Accelerator Center (SLAC) will produce intense, coherent 0.15 nm x-rays, with an expected peak brightness many orders of magnitude greater than existing x-ray sources and energy density as high as 4 x 10{sup 25} watts/cm{sup 2}. These x-rays are produced by a single pass of a 15 GeV electron beam through a long undulator. The 15 GeV electron beam is generated using the last one third of the existing SLAC linac. This paper describes how to extend the present design of the LCLS to generate even shorter x-ray pulses than the nominal 255 femtoseconds FWHM. The goal of this study is to obtain pulse lengths as short as 50 femtoseconds. The scientific need for the shorter bunches is outlined, and electron and x-ray pulse compression options are reviewed. The analysis concludes that there are paths, albeit difficult, to obtaining shorter bunches and that the present LCLS design has the flexibility and range to test these paths.