2-PHOTON EXCITATION PROCESSES AND LINEWIDTHS OF SURFACE AND IMAGE STATES ON CU(111)

The occupied surface state and the first image state on Cu(111) have b een observed by high-resolution, two-photon photoemission as a functio n of photon energy. A pronounced narrowing of the linewidth is found f or the resonant excitation from the occupied surface state into the fi rst image state. The product of two Lorentzians convoluted with a Gaus sian leads to a satisfactory description of the complete series of spe ctra. The intrinsic linewidth of the first image state on Cu(111) is o btained as 85 +/- 10 meV, in agreement with recent time-resolved measu rements. The occupied surface state has an intrinsic linewidth of 65 /- 15 meV, as also observed in one-photon photoemission experiments. ( C) 1997 Elsevier Science B.V.