Surface Acoustic Wave Enhancement of Photocathode Perfomance

Novel electron gun features are required to enhance the peak and/or average beam brightness by reducing the emittances of electron bunches while allowing the guns to operate at a high repetition rate using laser excitation of the photocathode. The generation of surface acoustical waves (SAWs) on piezoelectric substrates is known to produce strong piezoelectric fields that propagate on the surface of the material. These fields can significantly suppress recombination effects and result in enhanced quantum efficiency of photoemission. This project is developing the novel use of SAWs on photocathodes to control their emittances and improve their efficiency, so that lower-power lasers can generate more intense electron beams having smaller emittances. State-of-the-art computer simulations will be developed for a device that uses Interdigital Transducers (IDT) placed on GaAs photocathode wafers to generate SAWs with the required traveling and standing wave properties to demonstrate control of the electron-hole recombination rate. The experimental apparatus to demonstrate suppression of electron-hole recombination as a function of SAW parameters will be designed and sample SAW devices will be fabricated. Measurements of the quantum efficiency of the photocathode and the beam emittance are planned for Phase II. We propose to enhance the performance of photocathode-based electron sources with a new feature, surface acoustical waves. High-current, low-emittance electron sources are needed for generation of significantly brighter electron beams than currently available to be used for electron accelerators. Photoemission enhancement techniques will be developed for production of more efficient photocathode operation. The improved quantum efficiency and parameter control expected from the use of SAW will be useful for electron accelerators, while the commercialization in such widespread fields as photon detectors and electron microscopy is also compelling.