A MODE-LOCKED PULSE PRE-AMPLIFIER FOR PHOTOCATHODE ILLUMINATION

MODE-LOCKED LASER PULSES ARE REQUIRED FOR GENERATING BURSTS OF ELECTRONS FROM PHOTOCATHODES. THESE ELECTRONS ARE USED TO SEED LINEAR ACCELERATORS AND FREE ELECTRON LASERS. THE PHOTOCATHODES ARE TYPICALLY ILLUMINATED WITH 10 TO 100 MUJ PER PULSE OF ENERGY IN THE ULTRAVIOLET. DIODE-PUMPED ND:YLF AND ND:YAG MODE-LOCKED OSCILATORS HAVE RECENTLY BEEN DEVELOPED WITH LOW TIMING JITTER AND REPETITION RATES AROUND 100 MHZ THAT ARE THE PREFERRED FRONT END FOR THE PHOTOCATHODE ILLUMINATION SYSTEMS. THE APPLICATION REQUIRES SELECTING A 1 TO 10 MUS LONG SECTION OF THE MODE-LOCKED PULSE TRAIN FOR AMPLIFICATION BY 40 TO 60 DB; THIS IS CURRENTLY ACHIEVED WITH A POCKELS CELL SWITCHING TECHNOLOGY AND A TWO OR THREE STAGE LAMP-PUMPED AMPLIFIER CHAIN. THIS PHASE I EFFORT PLANS A DIODE-PUMPED MULTIPASS PRE-AMPLIFIER TO INCREASE PULSE ENERGIES FROM A DIODE-PUMPED MODE-LOCKED OSCILLATOR BY 20 TO 30 DB, ELIMINATING THE NEED FOR ONE OR TWO OF THE LAMP-PUMPED STAGES. IT ALSO PLANS A PULSE SELECTION TECHNIQUE USING AN ACOUSTO-OPTIC BRAGG MODULATOR. THE DIODE-PUMPED PREAMPLIFIER WOULD GENERATE PULSE TRAINS WITH ENERGIES UP TO ABOUT ONE MUJ PER PULSE, WITH BETTER STABILITY AND RELIABILITY THAN THE LAMP-PUMPED AMPLIFIER STAGE. THE GOALS OF THIS PROJECT ARE TO CHARACTERIZE THE DIODE-PUMPED AMPLIFIER, DEMONSTRATE PULSE-TRAIN MACROPULSE SELECTION USING AN ACOUSTO-OPTIC GRAGG MODULATOR, AND TO INVESTIGATE AMPLIFER EFFECTS ON PULSEWIDTH SUCH AS GAIN NARROWING AND GAIN SATURATION.