Observation of Two-photon Photoemission from Cesium Telluride Photocathodes Excited by a Near-infrared Laser

TL;DR

This study demonstrates two-photon photoemission from cesium telluride photocathodes using near-infrared laser pulses, revealing nonlinear photoemission behavior with potential implications for photocathode performance.

Contribution

It is the first to observe two-photon photoemission from Cs$_2$Te photocathodes excited by near-infrared laser pulses, contrasting with previous three-photon processes in metals.

Findings

Two-photon photoemission observed in Cs$_2$Te with 800-nm laser.

Quantum efficiency defined for nonlinear photoemission processes.

Charge versus laser energy studied and compared with copper photocathodes.

Abstract

We explore nonlinear photoemission in cesium telluride (Cs$_2$Te) photocathodes where an ultrashort ($\sim 100$ fs full width at half max) 800-nm infrared laser is used as the drive-laser in lieu of the typical $\sim 266$-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., \emph{Phys. Rev. Lett.}, \textbf{104}, 084801 (2010)], a metallic photocathode. We particularly observe two-photon photoemission in Cs$_2$Te using the infrared laser in contrast to the anticipated three-photon process as observed for metallic photocathodes.