Phase noise reduction and photoelectron acceleration in a high-Q RF gun

The phase noise and jitter characteristics of the laser and RF systems of a high-gradient X-band photoinjector have been measured experimentally. The laser oscillator is a self-mode-locked titanium:sapphire system operating at the 108th subharmonic of the RF gun. The X-band signal is produced from the laser by a phase-locked dielectric resonance oscillator and amplified by a pulsed TWT and klystron. A comparison between the klystron and TWT amplifier phase noise and the fields excited in the RF gun demonstrates the filtering effect of the high-Q structure, thus indicating that the RF gun can be used as a master oscillator and could be energized by either an RF oscillator, such as a magnetron, or a compact source, such as a cross-field amplifier. In particular, the RF gun can play the role of a pulsed RF clock to synchronize the photocathode laser system; direct drive of a synchronously mode-locked AlGaAs quantum well laser has been achieved using the X-band gun RF fields. This novel, gigahertz repetition rate, laser system is being developed to replace the more conventional femtosecond Ti:Al₂O₃ system. Some advantages include pumping this laser with a stabilized current source instead of a costly, low-efficiency pump laser. Finally, dark current measurements and initial photoelectron measurements are reported