Manipulating Light in 3+1 Dimensions Using Sharp Tips

The strongly enhanced optical near-field at the apex of a sharp tip can be used to break the diffraction barrier in scanning near-field optical microscopy, producing optical images with single-digit nanometer-scale resolution and enabling optical investigations of mesoscale hierarchical systems at nearly all relevant length scales.  The near-field interactions between a single emitter and the tip can also modify the local density of optical states, which can impart control over various optical properties of the emitter.  For example, by spatially scanning the tip in 3D close to the emitter, the emission direction (+1D) and polarization (+1D) can be simultaneously controlled.  Furthermore, temporal (+1D) fluctuations in the emission signal from, for example, semiconductor nanocrystal quantum dots, can be suppressed by balancing the near-field excitation enhancement with the fluorescence quenching rate, which varies as the QD blinks.  Together, these three +1D controls may enable the realization of a true single photon source where a photon in a particular polarization state can be delivered to a particular location at a particular time.