Recent technological developments make it possible to consider use of the Stanford linear accelerator to drive a linac coherent light source (LCLS)—a laser operating at hard x-ray wavelengths. In the LCLS, stimulated emission of radiation would be achieved in a single pass of a high-energy, extremely bright electron beam through an undulator, without the optical cavity resonator normally used in storage ring-based free-electron lasers. The x-ray laser beam would be nearly diffraction limited with very high transverse coherence, and would exhibit unprecedented peak intensity and peak brightness, and sub-picosecond pulse length. Such an x-ray source offers unique capabilities for a large number of scientific applications.

Free electron lasers have the promise of producing extremely high-intensity short pulses of coherent, monochromatic radiation in the 1-10 keV energy range. For example, the Linac Coherent Light Source at Stanford is being designed to produce an output intensity of 2x10 14 W/cm 2 in a 230 fs pulse. These sources will open the door to many novel research studies. However, the intense x-ray pulses may damage the optical components necessary for studying and controlling the output. At the full output intensity, the dose to optical components at normal incidence ranges from 1-10 eV/atom for low-Z materials (Z<14) at photon energies of 1 keV. It is important to have an understanding of the effects of such high doses in order to specify the composition, placement, and orientation of optical components, such as mirrors and monochromators. Doses of 10 eV/atom are certainly unacceptable since they will lead to ablation of the surface of the optical components. However, it is not precisely known what the damage thresholds are for the materials being considered for optical components for xray free electron lasers. In this paper, we present analytic estimates and computational simulations of the effects of high-intensity x-ray pulses on materials. We outline guidelines for the maximum dose to various materials and discuss implications for the design of optical components.

No abstract