Solid immersion lens-enhanced micro-photoluminescence: principle and   applications
  We demonstrate the combination of a hemispherical solid immersion lens with a micro-photoluminescence setup. Two advantages introduced by the SIL, an improved resolution of 0.4 times the wavelength in vacuum and a 5 times enhancement of the collection efficiency, make it an ideal system for spatially resolved spectroscopy applications. The influence of the air gap between the SIL and the sample surface is investigated in detail. We confirm the tolerance of the set--up to an air gap of several micrometers. Such a system is proven to be ideal system in the studies of exciton transport and polarization dependent single quantum dot spectroscopy. 
S. Moehl, Hui Zhao, B. Dal Don, S. Wachter, and H. Kalt