Publications

A semiconductor quantum-optical theory is developed and applied to address questions involving thresholdless lasing and increasing single-photon production rate. Excitation dependences of intensity, coherence time, photon autocorrelation function and carrier spectral hole burning are described.

We study theoretically the performance of electrically pumped self-organized quantum dots as a gain material in the mid-IR range at room temperature. We analyze an AlGaAs/InGaAs based structure composed of dots-in-a-well sandwiched between two quantum wells. We numerically analyze a comprehensive model by combining a many-particle approach for electronic dynamics with a realistic modeling of the electronic states in the whole structure. We investigate the gain both for quasiequilibrium conditions and current injection. Comparing different structures, we find that steady-state gain can only be realized by an efficient extraction process, which prevents an accumulation of electrons in continuum states, that make the available scattering pathways through the quantum dot active region too fast to sustain inversion. The tradeoff between different extraction/injection pathways is discussed. Comparing the modal gain to a standard quantum-well structure as used in quantum cascade lasers, our calculations predict reduced threshold current densities of the quantum dot structure for comparable modal gain. Such a comparable modal gain can, however, only be achieved for an inhomogeneous broadening of a quantum-dot ensemble that is close to the lower limit achievable today using self-organized growth.

We have theoretically and experimentally investigated the possibility of single atom deposition using laser cooled sources. In our theoretical work, we investigated an atom source composed of out-coupling from a Bose-Einstein condensate in a trap. A model was developed for Bose-Einstein-condensate-based devices. To illustrate its application, a 2-well system is studied. The results show interesting and possibly useful differences between operation with coherent (phased-locked) and incoherent (unlocked) population transfer between levels in the two wells. The two modes of operation are governed by an interplay among scattering, energy renormalizations and coupling between wells. In parallel, we have experimentally investigated the possibility of controlled deposition of single cesium atoms onto surfaces using optical tweezers. We have measured the rate limit for translation of single atoms in optical tweezers to be 45 mm/s for stepped translation, and have constructed an apparatus for deposition of single atoms on a sapphire substrate for future work.

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A revolution in lighting is well on its way. Rewind the clock a year or so and the prices of LED bulbs made many shoppers wince. But now it is possible to get a high-quality 60 W equivalent for well under $10, and that’s allowing sales of LED bulbs incorporating chips from the likes of Cree and Philips Lumileds to take off. Although these solid-state bulbs are much more pricey than incandescents, which have largely disappeared from shelves due to legislation, they more than make up for that additional up-front cost with a substantial trimming of the electricity bill. It is a more tricky decision, however, whether it makes more sense to buy an LED bulb or a cheaper compact fluorescent (CFL). In terms of durability, adaptability and environmental impact, the solid-state bulb is the clear winner. But both types of light are similar in the efficiency stakes, and thus the running costs.

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