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(MO-3-27)
J. Gubeli, R. Evans, A. Grippo, K. Jordan, M. Shinn, and T. Siggins
Jefferson Lab
Jefferson Laboratory's Free Electron Laser (FEL) incorporates a cesiated gallium arsenide (GaAs) DC photocathode gun as its electron source. By using a set of scanning mirrors, the surface of the GaAs wafer is illuminated with a 543.5nm Helium-Neon laser. Measuring the current flow across the biased photocathode generates a quantum efficiency (QE) map of the 1-inch diameter wafer surface. The resulting QE map provides a very detailed picture of the efficiency of the wafer surface. By generating a QE map in a matter of minutes, the photocathode scanner has proven to be an exceptional tool in determining cathode wear and availability.
FEL 2000