On-Chip Waveguide Integrated GaAs Photocathodes

The development of high brightness photocathodes is of significant importance in advancing the field of accelerator applications
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. One of the most prominent materials for such photocathodes is Cesiated-GaAs, owing to its high quantum efficiency and negative electron affinity
³
. To increase the efficiency of light coupling into the photoemissive surface, a waveguide in combination with a grating coupler has been introduced to facilitate the integration of the photoemission process. This was achieved by transferring a 40 nm thick layer of p-GaAs onto a nanofabricated Si3N4 waveguide through the epitaxial transfer method. The grating coupler was designed and positioned in front of the waveguide to optimize the transmission efficiency and effectively couple light into the waveguide. Furthermore, wavelength-dependent grating designs allow for the coupling of various wavelengths of light into the GaAs photoemissive surface. Absorption of photons by the GaAs layer through evanescent coupling can initiate new photoemission mechanisms, leading to brighter electron beams and enabling unprecedented shaping of emitted electrons. This research lays the groundwork for integrating photonics and nanofabrication advancements with photocathodes to create high brightness electron sources for accelerator applications.