| The use of free-electron lasers (FELs) is quickly expanding in electro-optics and other fields. FEL applications include nonlinear optics, photochemistry, and multiple stage amplification. These applications require a laser beam of known spatial characteristics. Previous theory and experiments have shown that gain amplitude guiding and refractive optical guiding of the laser beam by a narrower electron beam within the laser resonator is significant. Those experiments averaged over the longitudinal extent of the laser beam and were not designed to observe longitudinal effects.;In this dissertation I first report the results of a full spatial and temporal free-electron laser computer simulation code, FELEX, which was used to predict the behavior of the MKIII FEL at the Stanford Photon Research Laboratory. These results show that the optical guiding in short pulses has a monotonic dependence on longitudinal position, which is strongest at the trailing edge of the pulses.;Second, I describe the autocorrelation measurements performed on the MKIII. This was the first experiment designed to detect longitudinally dependent guiding within the picosecond optical pulses. The measurements were performed using a variable aperture in the far field of the laser beam. The dependence on electron beam parameters (pulse length) and resonator length detuning was studied. The results of this experiment were inconclusive because laser instability and drift was as significant as any observed effect. Nevertheless, an upper limit of a 5% difference in the peak value of the normalized autocorrelation functions with and without the aperture was measured.;Third, the development of sidebands, or optical spikes, was studied, and I present the autocorrelation results showing the growth of spikes. The experimental data agrees with the FELEX predictions. These autocorrelation results are the first observation of the spiking behavior in the time domain. |
