Observation of high gain and intensity fluctuations in self-amplified spontaneous emission free-electron lasers

This thesis presents the results of two recent free electron laser (FEL) experiments operating in the self amplified spontaneous emission (SASE) mode.; An X-ray laser would offer a unique way to explore the structure of matter at the atomic and molecular scale. Among the various schemes proposed to reach this wavelength region, the free electron laser, operating without mirrors in a self amplified spontaneous emission mode offers a favorable scaling law. It has also been shown that utilizing state of the art linear accelerators and electron sources it is possible to build an X-ray SASE FEL, and this has led to two major proposals to build a SASE X-ray FEL, one at SLAC, the other at DESY.; The theory on which the SASE X-ray FEL is based, has been developed over many years, but the experimental data to support it are few and incomplete. Very large gain in SASE has so far been observed in the centimeter to millimeter waves, and in the medium infrared (IR) at Los Alamos; recently gain in the near IR has been observed at Orsay and at Brookhaven. The intensity distribution function has been previously measured only for spontaneous undulator radiation, with no amplification, and long bunches. This thesis analyzes two recent experiments designed to verify the models of high gain FELs.; High gain FEL theory is reviewed with a emphasis on the characteristics of SASE measurable by these experiments. The accelerator, beamline components and diagnostics are described with an emphasis on the measurements. The FEL undulators and optical diagnostics are also described, again with an emphasis on the measurements.; The experimental data are compared to analytic models, where applicable, and to computer simulation codes.