Measurements Of The Dispersive And Absorptive Properties Of The Free-electron-laser Gain Medium

Measurements of the dispersive and absorptive properties of the free-electron-laser gain medium carried out on the United Kingdom Free Electron Laser Scotland are presented. We show how measurements of gain can be used, both with and without the optical cavity, to establish the correct cavity length for synchronism and determine important physical parameters. We present results of optical injection experiments.