Resonant electron emission of silver spheroids induced by laser surface plasmon excitation

Laser excitation of surface plasmons on a silver granular surface has been studied as a function of light frequency. Both light absorption and electron emission have been measured by varying continuously the wavelength between 275 and 700 nm. Resonance effects at the Fröhlich frequencies of the silver spheroids are displayed and a correlation between absorption and emission is clearly exhibited. The lux-ampere characteristics performed at selected increasing wavelengths display slopes with integer orders, indicating that the emission process remains a photoeffect even in the presence of a surface-plasmon resonance. The photoemission process shows net switches of these slopes that turn from linear into quadratic and then cubic integer values. The position of the first switch yields W_s = 4.15 ± 0.05 eV for the work function of the granular surface. The position of the second switch defines the threshold energy for the two-photon emission process, which is found to differ significantly from the expected photon minimum energy (Latin small letter h with stroke sign)ω = 1/2 W_s.