Self-amplified spontaneous emission in a free-electron laser has been proposed for the generation of very high brightness coherent x-rays. This process involves passing a high-energy, high-charge, short-pulse, low-energy-spread, and low-emittance electron beam through the periodic magnetic field of a long series of high-quality undulator magnets. The radiation produced grows exponentially in intensity until it reaches a saturation point. We report on the demonstration of self-amplified spontaneous emission gain, exponential growth, and saturation at visible (530 nanometers) and ultraviolet (385 nanometers) wavelengths. Good agreement between theory and simulation indicates that scaling to much shorter wavelengths may be possible. These results confirm the physics behind the self-amplified spontaneous emission process and forward the development of an operational x-ray free-electron laser.

Dase measurements made fin and around the insertion devices (IDS) at the Advanced Photon Source are reported. Attempts ar? made to ;c'mpare these dose rates to dose rate> that ha\? been reported to cause rndintipn-induced demagnctlrxion. bur comparisons are complicalted by such factors as the particular magnet material and the techniques used in its manufacture, the spectrum and type of radiation. and rhe demagnetizing field seen by the m.~gnet. The spectxm of radiation at the IDS ha5 been measured .~nd found to include J larse high-energy (7 GeV) component, at least durin,a some runs. Lead shielding installed immediately upstream of the IDS has been found to decrease the dose to the upstream ends of the IDS. It has almost no effect on the dose to the downstream ends of the IDS, however. since much of the radiation travels through the ID vacuum chamber and cannot be readily shielded. Opening the gaps of the IDS during injection and at other times also helps decrease the radiation exposure. INTRODUCTIOS

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