We report single-mode and multimode lasing from isolated spherical liquid microcavities containing CdSe/ZnS nanocrystal quantum dots. Lasing is observed at densities more than 2 orders of magnitude lower than previously demonstrated or theoretically predicted, assuming a uniform nanocrystal quantum dot distribution. Charged droplets, between 10 and 40 microm in size, are electrodynamically levitated and optically pumped. Substantial laser signals at low thresholds are measured from the directional emission normal to the pump beam, owing to the high Q cavity modes.

Investigations on the breakdown and the maintenance phase in a pulsed N 2 microwave plasma at 2.45 GHz under low pressure (1-10 mbar) have been carried out.The discharge chamber has a cylindrical geometry with a length of 80 mm and a radius of 45 mm. Microwave pulses with a duration of 50-200 µs and a repetition rate of 10-500 Hz were typical for the experiments. The behaviour of the electric field in the duct has been measured and calculated. The electron number density has been determined using an HCN laser interferometer and a Langmuir probe. The microwave power absorbed in the plasma was obtained measuring the forwardly directed and the reflected time resolved power flux. The vibrational excitation of the N 2 molecules in the plasma was studied with spatial and temporal resolution on the basis of the coherent anti-Stokes Raman scattering (CARS) technique.

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The index of refraction, the extinction coefficient, and the absorptance for gold and tin were measured in a temperature range from room temperature up to the melting point for the wavelength λ=10.6 μm. All measurements were performed under ultrahigh-vacuum conditions using a photometric infrared ellipsometer with a rotating analyzer. Measurements verify a discontinuous jump of the absorptance at the solid-to-liquid phase transition from 3.5 to 6.5% in the case of gold and from 4.9 to 9.2% in the case of tin. The experimental results derived for the clean solid surface are in good agreement with the theoretical prediction by a Drude model, if additionally appropriate effective masses and the anomalous skin effect are taken into account. This theory is much less accurate if applied to the molten state of gold and tin, as was already shown previously for liquid aluminum and copper.

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