FREE-ELECTRON LASER OSCILLATOR FOR SIMULTANEOUS NARROW SPECTRAL RESOLUTION AND FAST TIME RESOLUTION SPECTROSCOPY

摘要

A technique for increasing the temporal resolution of the optical pulses whitesimultaneously increasing the spectral resolu-tion of the pulse train in a free-electron laser. The increase in temporalresolution is achieved by introducing a quadratic temporalphase variation (i.e. linear frequency chirp) across the optical pulses, andthen propagating the outcoupled pulses through a dis-persive delay line such as a grating pair or prism pair in order to compressthem to the transform limit of the broadened spec-trum. Essentially, the quadratic time dependence of the optical phase broadensthe spectrum and yields Fourier componentswhose phase exhibits a quadratic frequency dependence. To operate a free-electron laser in such a configuration, electron micro-pulses with a linear time-dependent energy are produced in the RF linac bypositioning the bunches slightly off the peak of theRF wave at phases where the field gradient is large. These electronmicropulses are injected into the wiggler and lead to the for-mation of optical pulses with a corresponding linear time-dependent frequency.