Ultrahigh spatiotemporal resolved pump-probe signal on a metal nanostructure is detected by femtosecond-SNOM. By using two-color pump-probe configuration, ultrafast hot electron transportation is clearly observed on a time scale of a few hundred femtoseconds. (C) 2010 Optical Society of America
Ultrahigh spatiotemporal resolved pump-probe signal near a gold nano-slit is detected by femtosecond-SNOM. By employing two-color pump-probe configuration and probing at the interband transition wavelength of the gold, signal contributed by surface plasmon polariton is avoided and spatiotemporal evolvement of excited electrons is successfully observed. From the contrast decaying of the periodical distribution of the pump-probe signal, ultrafast diffusion of excited electrons with a time scale of a few hundred femtoseconds is clearly identified. For comparison, such phenomenon cannot be observed by the one-color pump-probe configuration. (C) 2010 Optical Society of America