Two-photon Pumped Lasing
Ocean NanoTech and its collaborators has demonstrated upconverted lasing in the nonlinear, two-photon absorption using colloidal nanocrystal quantum dots (NQDs). Upon pulse excitation at sub-band gap photon energies the radiative recombination of excitons in close-packed CdSe/CdS/ZnS core-shell NQDs were found to be sufficiently fast to compete with the intrinsic non-radiative Auger recombination, that was confirmed by the presence of a fast decay (7 ps)in the time-resolved photoluminescence.
Colloidal semiconductor nanocrystal quantum dots (NQDs) have recently emerged as a unique material for constructing lasers operated in the strong quantum confinement regime arising from the dramatically reduced dimensionality. Quantum dot (QD) lasers offer the potential for a low and temperature insensitive lasing threshold, continuous spectral tenability over a broad and technically important wavelength range, and scalable device configuration. Since Klimov et al. first reported the amplified spontaneous emission (ASE) in UV-excited Cd(SSe) NQDs, ASE and lasing from colloidal semiconductor NQDs have been realized with a variety of photonic structures including micro rings, microspheres, photonic crystals, and distributed-feedback resonators. These optically pumped NQD lasers find promising applications from light wave communications and biological–chemical sensing to medical diagnosis.
The NQDs employed in this study have core-shell structures consisting of CdSe crystalline cores and CdS/ZnS double shells, prepared with a synthetic route based on inorganic precursors and non-coordinating solvents. The average size of the as prepared core-shell nanocrystals is 6 nm in diameter. Following the nanocrystal purification process, thin films of NQDs were spun cast from a toluene solution
to form slab waveguides on SiO2-coated quartz substrates. In the slab waveguide the nominal thickness of the nanocrystal core layer is 500 nm, whereas the bottom SiO2 cladding layer is 1 m thick, deposited via plasma-enhanced chemical vapor
deposition (PECVD). 0No. 0
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*Chunfeng Zhang, Fan Zhang, Ting Zhu, An Cheng, Jian Xu,Qi Zhang, Suzanne E. Mohney, Ron H. Henderson, and Y. Andrew Wang, “Two-photon-pumped lasing from colloidal nanocrystal quantum dots,” OPTICS LETTERS, Vol. 33, No. 21, 2437-2439, Nov. 1, 2008.