MODE CONTROL ON SHORT-PULSE FELS USING A MICHELSON-MIRROR RESONATOR

We have studied the effects of a Michelson-mirror resonator on the axial optical mode structure of short-pulse FELs driven by an rf linac. By providing an extra delay of one rf period in the secondary arm of the interferometer, successive micropulse in the macropulse can be coupled via the beam splitter and be made to build up from noise with a definite phase relationship. We describe one-dimensional simulations of the FEL interaction with Gaussian resonator modes, including both shot noise and quantum noise, for practical resonator configurations, and derive a linear analysis which accurately predicts the evolution of the axial mode structure. Finally, we discuss applications to high-resolution spectroscopy and describe preliminary experimental results using the Mark III FEL. © 1990.