No abstract

We report measurements of very large output intensities corresponding to a gain larger than 10 5 for a single pass free-electron laser operating in the self-amplified spontaneous emission (SASE) mode at 12 mm. We also report the observation and analysis of intensity fluctuations of the SASE radiation intensity in the high-gain regime. The results are compared with theoretical predictions and simulations. [S0031-9007 (98)07403-1]

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Cesium telluride (Cs2Te) photocathodes, with quantum efficiencies (QEs) of 15%–18% at 251 nm, were fabricated by vapor deposition of Te and Cs onto a Mo substrate and used as an electron source for the Los Alamos Advanced Free-Electron Laser. In the fabrication chamber, the spectral response from 251 to 578 nm was measured before and after a controlled exposure of several photocathodes to air. The 251-nm QE dropped by about a factor of 20 when exposed to 2×10−4 Torr of air for 1 h. Heating degraded photocathodes to 150–200 °C partially rejuvenated their QEs to about 60% of the value before air exposure. The performance of Cs2Te as a source of electrons for accelerators was evaluated in the photoinjector stage of the Advanced Free-Electron Laser. The response time, saturation level, and dark current of cesium telluride photocathodes and the emittance and energy spread of the resulting electron beam were determined to be sufficient for free electron laser applications.

We report the first high-gain self-amplified spontaneous emission experiment at 15 mm driven by a high-brightness 17-MeV electron beam. A change of two decades in the beam current yields an increase of four decades in the measured infrared power. By fitting the measured infrared pulse energy to an analytic model, we estimate that eight power gain lengths, corresponding to a gain of 300, exist in the wiggler at 279 A. [S0031-9007 (98)06692-7] PACS numbers: 41.60. -m