DEPRESSED PHOTOEMISSION FROM GORLICH CATHODES AT HIGH LASER-LIGHT INTENSITIES

The current density of electrons emitted from surfaces irradiated by light is known to follow either a linear or quadratic dependence with intensity for single- or double-photon absorption respectively or, at high incident light intensities, a square root dependence (depressed photoemission). In separate experiments, a Gorlich (Cs3Sb) cathode was irradiated 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 intensities of up to five orders of magnitude higher than previously observed threshold values with no apparent evidence of saturation of the effect. The consequences of this are discussed in relation to surface traps and two-photon-plasmon excitation in the photocathode. (C) 1995 American Institute of Physics.