REAL-TIME ELLIPSOMETRY FOR MONITORING THE GROWTH OF CESIUM-TELLURIDE PHOTOCATHODES

Semiconductor photocathodes, especially Cesium-Telluride photocathodes, are vital for generation of high brightness electron beams used in free-electron lasers. However the quantum efficiency and lifetime depends critically on manufacturing and operational conditions. Monitoring the formation of the photocathode is essential for understanding these dependencies. For example, the deposition rate of the Cs correlates to the quantum efficiency and adversely correlates to the lifetime. We will discuss the use of ellipsometry for monitoring the formation of the photocathode, describe our experimental configuration and discuss preliminary results obtained with Cesium-Telluride photocathodes. These results seems to indicate that ellipsometry is a viable method for monitoring the formation of these photocathodes.