Sub-wavelength microscopy of surface plasmon oscillations and their statistical properties

Near-field microscopy of plasmons generated in different layer structures is performed by means of a scanning tunnelling microscope. The signal fluctuations are statistically evaluated for the first time. The direct plasmon signal shows a narrow Gaussian or Poisson-like distribution, whereas the thermal signal of the plasmon oscillation corresponds to a Boltzmann-type distribution as expected for a signal of thermal origin. The width of the direct plasmon signal corresponds in most cases to the width expected for an ideal Poissonian or is narrower. If the signal fluctuations resulted uniquely from intensity variations in time, this would indicate reduced shot noise. Unfortunately, the setup cannot separate the fluctuations due to location and time. Nevertheless, the results indicate that further investigations on the statistics of plasmon would be interesting.