Whispering gallery modes in indium oxide hexagonal microcavities

We report on the use of In₂O₃nanowires with hexagonal cross section as optical whispering gallery resonators. The single-crystal In₂O₃nanowires were fabricated by an in situ thermal oxidation method. Whispering gallery modes(WGMs) in the visible spectral range were directly observed at room temperature. Due to the slight tapering of the nanowires, the energies and orders of the WGMs were modulated when excitations were scanned along the c-axis (length) of the nanowires. The experimental results were explained and fitted well with a plane wave interference model and Cauchy dispersion formula for refractive indices.The work is funded by the NSFC 973 projects and STCSM of China Grant Nos. 2004CB619004 and 2006CB921506. The authors thank the Australian Government Department of Innovation, Industry, Science and Research for funding this collaborative research under the International Science Linkages China Program

Single-crystalline hexagonal ZnO microtube optical resonators

High quality ZnO microtubes with hexagonal cross sections, fabricated via an oxidation-sublimation process, are studied as novel optical resonators. Whispering gallery modes, Fabry-Pérot modes, and an additional set of modes with different polarization

Weak lasing in one-dimensional polariton superlattices

Bosons with finite lifetime exhibit condensation and lasing when their influx exceeds the lasing threshold determined by the dissipative losses. In general, different one-particle states decay differently, and the bosons are usually assumed to condense in the state with the longest lifetime. Interaction between the bosons partially neglected by such an assumption can smear the lasing threshold into a threshold domain—a stable lasing many-body state exists within certain intervals of the bosonic influxes. This recently described weak lasing regime is formed by the spontaneously symmetry breaking and phase-locking self-organization of bosonic modes, which results in an essentially many-body state with a stable balance between gains and losses. Here we report, to our knowledge, the first observation of the weak lasing phase in a one-dimensional condensate of exciton–polaritons subject to a periodic potential. Real and reciprocal space photoluminescence images demonstrate that the spatial period of the condensate is twice as large as the period of the underlying periodic potential. These experiments are realized at room temperature in a ZnO microwire deposited on a silicon grating. The period doubling takes place at a critical pumping power, whereas at a lower power polariton emission images have the same periodicity as the grating

THE DETERMINATION OF VIBRATIONAL RELAXATION RATE OF PbS* A (0(+)) BY LASER-INDUCED FLUORESCENC TECHNIQUE

The vibrational relaxation rates of PbS*A(0(+)) state in Ar and S-2 have been studied by laser induced fluorescence technique. The vibrational relaxation rate of PbS*A(0(+)) in S-2 is two orders of magnitude larger than in Ar. Formation of unstable intermediate PbS3 may be responsible for the fast relaxation,The energy transfer process between A(0(+))(V' = 19) and B(1)(V' = 6) states is also suggested

Spin dependence of the magnetization step in the Pr-doped manganites

Magnetic measurements were performed to study a single crystal Pr0.5Sr0.5MnO3 and polycrystalline Pr0.6Ca0.4MnO3. Magnetic-field$\hbox{--}$induced magnetization step is observed at low temperature for Pr-doped phase-separated manganites. Magnetization measurements indicate that the spin-stiffness constant D exhibits large magnetic-field dependence. Moreover, there exists a remarkable change of the spin-stiffness constant corresponding to the variety of the step-like magnetization. Our results suggest that the spin-wave inherent to the coexistence of the antiferromagnetic and ferromagnetic phases plays a crucial role in the mechanism of these magnetic transformations

Temperature-dependent Raman spectra of bamboo-like boron nitride nanotubes

Phonon properties of boron nitride nanotubes (BNNTs) were investigated using Raman spectroscopy at different temperatures and new sp3- bonded BN vibrations were identified. The Raman peak of the E2g mode of BNNTs is found to be downshifted and broadened compared to that of hexagonal BN at the same temperature. By increasing the temperature, the energy of the E2g mode and the sp3-bonding mode are downshifted, with the temperature coefficients being -0.010 and -0.069cm-1/K, respectively. We attribute this downshifting to anharmonic effects as well as the elongation of the B-N bond in BNNT structures with increasing temperature. © 2014 The Japan Society of Applied Physics