Comparison between a FEL amplifier and oscillator

Previous experiments with the Raman FEL, situated at the Twente University, showed that the output was influenced by the rather strong increase of the current density with time . The field emission diode has been modified to produce a more constant current pulse to simplify the analysis of the measurements . This resulted in a lower current density of the electron beam . With this new diode two set-ups are studied . In the first set-up the laser is still configured as an amplifier whereas m the second set-up the laser configuration is changed into an oscillator using a Bragg reflector with a space-variable corrugation height . For both set-ups we measured the frequency spectrum for specific values of undulator and guide magnetic fields . The relative performance of the amplifier and the oscillator configuration will be presented .