PHOTOELECTRON EMISSION IN FEMTOSECOND LASER-ASSISTED SCANNING-TUNNELING-MICROSCOPY

Direct illumination of the tunneling gap in an ultrahigh vacuum scanni ng tunneling microscope with ultrashort pump-probe laser pulses may of fer ultimate spatial and temporal resolution in surface experiments. T he electronic bandwidth of the tunneling gap (< 1 THz) does not limit the time resolution. Our experiments show that multiphoton photoelectr on emission from the sample limits the application of this detection s cheme at high laser fluence. However, a substrate specific pump-probe effect in the photoelectron yield with femtosecond transients is obser ved on Tantalum and on GaAs(110) surfaces.