Photoluminescence scanning near-field optical microscopy on III-V quantum dots

We show photoluminescence images of buried quantum dots with a spatial reso lution better than 250 nm. Uncoated fibre tips are used in shared aperture mode to illuminate and to detect the excited photoluminescence intensity in the optical near-field of thr sample. In a recent publication [1], it was shown that observing only the reflected light using uncoated fibre tips in shared aperture mode it is impossible to exceed the Rayleigh diffraction li mit. Nevertheless, by detecting the photoluminescence intensity we demonstr ate here that a sub-wavelength spatial resolution of approximately lambda/5 = 250 nm can be achieved. The comparison of far-field and near-field spect ra leads to the mechanism of spatial resolution and intensity enhancement i n this experiment. The PL intensity is dominated by the coupling of the unc oated fibre tip with the luminescent quantum dot and has an exponential dec ay with the sample probe distance.