DEPRESSED PHOTOEMISSION FROM GORLICH CATHODES AT HIGH LASER-LIGHT INTENSITIES

The current density of electrons emitted from surfaces irradiated by l ight is known to follow either a linear or quadratic dependence with i ntensity for single- or double-photon absorption respectively or, at h igh incident light intensities, a square root dependence (depressed ph otoemission). In separate experiments, a Gorlich (Cs3Sb) cathode was i rradiated with the green (lambda=5140 Angstrom) and blue (lambda=4880 Angstrom) lines of an Ar+ laser at various intensities in an effort to determine over what range depressed photoemission continued above the current density threshold of about 10(-5) A cm(-2). The results have confirmed and extended the existence of depressed photoemission to int ensities of up to five orders of magnitude higher than previously obse rved threshold values with no apparent evidence of saturation of the e ffect. The consequences of this are discussed in relation to surface t raps and two-photon-plasmon excitation in the photocathode. (C) 1995 A merican Institute of Physics.