Tuesday, 12 October 2004 - 4:45 PM

This presentation is part of : Sub-wavelength Nanostructuring I

Infrared room temperature lasing of nanoparticles coated on a dielectric microsphere

S. I. Shopova and A.T. Rosenberger. Oklahoma State University, Department of Physics, Stillwater, OK 74078-3072

Ultralow-threshold lasing has been achieved in fused-silica microspheres coated with semiconductor quantum dots. The cw Ti:sapphire pump input and laser output are efficiently coupled to and from whispering-gallery modes of the microresonator by tapered fibers.

Colloidally prepared spherical HgTe or HgCdTe nanoparticles (between 3 and 4 nm in diameter) were used as the active medium of the microlaser, because of their strong room temperature infrared photoluminescence. Depending on the stoichiometry, size distribution, and method of preparation, these nanoparticles (NPs) can exhibit a broad luminescence spectrum covering the telecommunication bands.

A spherical dielectric microcavity (of diameter between 500 and 1000 um) was used as a resonator. The optical quality factor Q of a typical microcavity before coating was greater than 108. The pump wavelength was 830 nm. The narrow laser line was slowly scanned through a cavity resonance. CW laser emission was observed. Emission spectra covering the range of 1240 nm to 1780 nm were measured using samples of NPs with different stoichiometry and sizes.

Near-thresholdless behavior (threshold less than the uncertainty of the linear fit to the data, 2 um) was observed. Taking into account losses due to scattering and to outcoupling via the second fiber, the 2-um upper limit on the threshold is an overestimate by an order of magnitude. We also find that either pump polarization (TE or TM) will produce laser emission of both polarizations, though the efficiencies differ.

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