Abstract
We explore the nonlinear photoemission in cesium telluride (Cs2Te) photocathodes where an ultrashort (∼100 fs full width at half max) 800-nm infrared laser is used as the drive-laser in lieu of the typical ∼266-nm ultraviolet laser. An important figure of merit for photocathodes, the quantum efficiency, we define here for nonlinear photoemission processes in order to compare with linear photoemission. The charge against drive-laser (infrared) energy is studied for different laser energy and intensity values and cross-compared with previously performed similar studies on copper [P. Musumeci et al., Phys. Rev. Lett. 104, 084801 (2010)], a metallic photocathode. We particularly observe two-photon photoemission in Cs2Te using the infrared laser in contrast to the anticipated three-photon process as observed for metallic photocathodes.
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