A GRATING SPECTROMETER FOR RAMAN FREE-ELECTRON LASER DIAGNOSTICS

A grating spectrometer is developed for Raman free electron laser (FEL ) diagnostics. Spectral measurements of a Raman FEL by a microwave gra ting spectrometer are presented. The aluminum reflection gratings with groove constant d = 7.5 mm, d = 3.5 mm and blaze angle theta = 30-deg rees are used. The spectrometer provides spectral coverage in the rang es of 6-10 mm and 2.2-4.8 mm with a resolution of 0.3 mm for an angle of incidence alpha = 60-degrees. The experimental results show that th e central frequency of the spectra decreases with increasing the wiggl er magnetic field, which is in accordance with the theoretical predict ions concerned with waveguide mode effects on the collective FEL. The spectrum of an FEL oscillator with distributed feedback cavity was mea sured. 3 mm FEL radiation using a small-period wiggler is obtained.