Two-photon photoemission from Ni (1 1 0) and (1 1 1) surfaces☆

Abstract Photoemission was observed when the samples were irradiated with photons in the energy range from 2.5 to 3.3 eV from a tunable dye laser with an intensity of 10 8 W cm −2 . The emission shows a quadratic intensity dependence. The variation with angle of incidence and polarization is different for the two surfaces. The result obtained from the (1 1 0) surface is discussed with help of the band structure as a two-photon surface photoelectric effect.