Article:Stevenson, R.M., Astratov, V.N., Skolnick, M.S. et al. (6 more authors) (2000) Continuous wave observation of massive polariton redistribution by stimulated scattering in semiconductor microcavities. Physical Review Letters, 85 (17 ReuseUnless indicated otherwise, fulltext items are protected by copyright with all rights reserved. The copyright exception in section 29 of the Copyright, Designs and Patents Act 1988 allows the making of a single copy solely for the purpose of non-commercial research or private study within the limits of fair dealing. The publisher or other rights-holder may allow further reproduction and re-use of this version -refer to the White Rose Research Online record for this item. Where records identify the publisher as the copyright holder, users can verify any specific terms of use on the publisher's website. TakedownIf you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing eprints@whiterose.ac.uk including the URL of the record and the reason for the withdrawal request. A massive redistribution of the polariton occupancy to two specific wave vectors, zero and ϳ3.9 3 10 4 cm 21 , is observed under conditions of continuous wave excitation of a semiconductor microcavity. The "condensation" of the polaritons to the two specific states arises from stimulated scattering at final state occupancies of order unity. The stimulation phenomena, arising due to the bosonic character of the polariton quasiparticles, occur for conditions of resonant excitation of the lower polariton branch. High energy nonresonant excitation, as in most previous work, instead leads to conventional lasing in the vertical cavity structure.

It is experimentally shown that barium titanate glass microspheres with diameters (D) in the range 2–220 μm and with high refractive index (n ∼ 1.9–2.1) can be used for super-resolution imaging of liquid-immersed nanostructures. Using micron-scale microspheres, we demonstrate an ability to discern the shape of a pattern with a minimum feature size of ∼λ/7, where λ is the illumination wavelength. For spheres with D > 50 μm, the discernible feature sizes were found to increase to ∼λ/4. Detailed data on the resolution, magnification, and field-of-view are presented. This imaging technique can be used in biomedical microscopy, microfluidics, and nanophotonics applications.

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Self-organized synthetic opals possessing a face centered cubic (fcc) lattice are promising for fabrication of a three-dimensional photonic crystal with a full photonic band gap in the visible. The fundamental limiting factor of this method is the large concentration of lattice defects and, especially, planar stacking faults, which are intrinsic to self-assembling growth of colloidal crystal. We have studied the influence of various types of defects on photonic band structure of synthetic opals by means of optical transmission, reflection and diffraction along different crystallographic directions. We found that in carefully chosen samples the stacking probability alpha can be as high as 0.8-0.9 revealing the strong preference of fcc packing sequence over the hexagonal close-packed (hcp). It is shown that scattering on plane stacking faults located perpendicular to the direction of growth results in a strong anisotropy of diffraction pattern as well as in appearance of a pronounced doublet structure in transmission and reflection spectra taken from the directions other than the direction of growth. This doublet is a direct manifestation of the coexistence of two crystallographic phases--pure fcc and strongly faulted. As a result the inhomogeneously broadened stop-bands overlap over a considerable amount of phase space. The latter, however, does not mean the depletion of the photonic density of states since large disordering results in filling of the partial gaps with both localized and extended states.

A polariton relaxation bottleneck is observed in angle-resolved measurements of photoluminescence emission from a semiconductor microcavity. For low power laser excitation, low k polariton states are found to have a very small population relative to those at high k. The bottleneck is found to be strongly suppressed at higher powers in the regime of superlinear emission of the lower polariton states. Evidence for the important role of carrier-carrier scattering in suppression of the bottleneck is presented.Semiconductor microcavities ͑MC's͒ with embedded quantum wells ͑QW's͒ have attracted great interest recently. In these structures, two-dimensional ͑2D͒ confinement of photon and exciton modes is realized. In high finesse MC's, as a result of exciton-photon coupling, mixed 2D polariton states occur 1 which exhibit a strong dependence of their properties on their relative exciton and photon contents. 2 In particular, due to the very small in-plane photon mass in MC's (M p Ϸ10 Ϫ4 m ex ), polaritons with a significant photon fraction have a very steep E -k dispersion curve, 3 and a density of states considerably smaller than that of excitons in a bare QW.Of particular relevance to the present work, energy relaxation in the polariton system is expected to be strongly modified relative to that of uncoupled excitons. Acoustic phonon scattering rates from high k exciton states into polariton states with wave vectors corresponding to the strong coupling regime (kр5 -6ϫ10 4 cm Ϫ1 ) are expected to be small due to the large energy transfer required compared to typical acoustic phonon energies of 1 meV. Furthermore, the strongly coupled states have very short radiative lifetime ͑ϳ1 psec͒ due to their high photon fraction, thus leading to a nonthermal polariton population and the occurrence of a relaxation bottleneck. Such bottleneck effects have been much discussed theoretically for the cavity polariton system. 4,5 References 4 and 5 calculate the expected population distributions for both upper and lower polariton branches, including exciton-phonon and exciton-exciton scattering. Very large depletions of the low k states, relative to those at high k, by factors up to 10 4 , are predicted. Such relaxation bottlenecks also occur in bulk semiconductors, 6 but are very difficult to study since the polaritons do not decay directly into external photons. In MC's, by contrast, direct polariton decay does occur due to photon leakage out of the cavity, permitting direct study of the population distribution. 7 A manifestation of the bottleneck has been observed in time-resolved measurements of the polariton emission in II-VI based microcavities. 8 The authors found an abrupt decrease of the polariton PL decay time when the character of the polariton states changed from photonlike to excitonlike. This observation indicates a slowdown of the relaxation process into polariton states with high photon fraction.In this paper, we present a definitive observation of the relaxation bottleneck for lower branch polaritons ͑LP's͒ from angle re...