Using a tunable optical microresonator with subwavelength spacing, we demonstrate controlled modulation of the radiative transition rate of a single molecule, which is measured by monitoring its fluorescence lifetime. Variation of the cavity length changes the local mode structure of the electromagnetic field, which modifies the radiative coupling of an emitting molecule to that field. By comparing the experimental data with a theoretical model, we extract both the pure radiative transition rate as well as the quantum yield of individual molecules. We observe a broad scattering of quantum yield values from molecule to molecule, which reflects the strong variation of the local interaction of the observed molecules with their host environment.

We study the dimensionality of the excitation transition dipole moment for single CdSe/ZnS core-shell nanocrystals using azimuthally and radially polarized laser modes. The comparison of measured and simulated single nanocrystal excitation patterns shows that single CdSe/ZnS quantum dots possess a spherically degenerated excitation transition dipole. We show that the dimensionality of the excitation transition dipole moment distribution is the same for all individual CdSe/ZnS nanocrystals, disregarding the difference in core size and irrespective of variations in the local environment. In contrast to the emission transition dipole moment, which is oriented in one plane, the excitation transition dipole moment of a single CdSe/ZnS quantum dots possesses an isotropy in three dimensions.

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A high-power optically pumped semiconductor laser operating around 970 nm has been used as a pumping source for an upconversion laser based on an Er3+ doped LiLuF4 crystal. Nearly 0.5 W of continuous wave (cw) output power and 0.8 W peak power at a 50% pump duty cycle could be achieved at a wavelength of 552 nm. This represents the highest output power from a room temperature upconversion laser ever reported. Laser threshold and slope efficiency were measured to be below 100 mW of absorbed pump power and 30%, respectively. This experiment could be an important step along the route to realizing a compact and efficient upconversion laser emitting in the Watt level power regime.