L. de S. Menezes

Controlled coupling of counterpropagating whispering-gallery modes by a single Rayleigh scatterer: a classical problem in a quantum optical light.

We present experiments where a single subwavelength scatterer is used to examine and control the backscattering induced coupling between counterpropagating high-Q modes of a microsphere resonator. Our measurements reveal the standing wave character of the resulting symmetric and antisymmetric eigenmodes, their unbalanced intensity distributions, and the coherent nature of their coupling. We discuss our findings and the underlying classical physics in the framework common to quantum optics and provide a particularly intuitive explanation of the central processes.

Blue upconversion enhancement by a factor of 200 in Tm3+-doped tellurite glass by codoping with Nd3+ ions

We investigated near-infrared-to-blue upconversion from thulium (Tm3+) doped in tellurite glasses upon continuous wave excitation near 800 nm. We observed an enhancement of over two orders of magnitude of the upconverted emission at ∼480 nm when neodymium (Nd3+) ions were codoped with Tm3+ ions. For comparison, using a Tm3+:Nd3+ codoped fluorozirconate glass as a reference material we observed a 40-fold enhancement of the blue emission. Analysis of the blue emission for samples with different doping levels of Nd3+ ions showed that energy transfer between Nd3+ and Tm3+ is the mechanism responsible for the enhancement in upconversion.

Continuous wave ultraviolet frequency upconversion due to triads of Nd3+ ions in fluoroindate glass

We have observed ultraviolet upconversion fluorescence from the 4D3/2 and 2P3/2 levels of Nd3+ in fluoroindate glass under infrared pumping. It was found that the excitation of a large population in the 4F3/2 metastable level allows to achieve strong upconversion emissions at 354 and 382 nm. A simple rate equation model reproduces the temporal behavior of the upconverted emission and allows us to estimate the energy transfer rate among three Nd3+ ions participating in the process.

Controlled photon transfer between two individual nanoemitters via shared high-Q modes of a microsphere resonator

We realize controlled cavity-mediated photon transfer between two single nanoparticles over a distance of several tens of micrometers. First, we show how a single nanoscopic emitter attached to a near-field probe can be coupled to high-Q whispering-gallery modes of a silica microsphere at will. Then we demonstrate transfer of energy between this and a second nanoparticle deposited on the sphere surface. We estimate the photon transfer efficiency to be about 6 orders of magnitude higher than that via free-space propagation at comparable separations.

Phonon-assisted cooperative energy transfer and frequency upconversion in a Yb3+/Tb3+ codoped fluoroindate glass

We report large thermal enhancement of the frequency upconversion (UC) process due to cooperative energy transfer (CET) in a Yb3+/Tb3+ codoped fluoroindate glass obtained by heating the sample from 308 to 530 K. To study the influence of multiphonon transitions in the UC process we chose anti-Stokes quasiresonant excitation of Yb3+ ions which were used as sensitizers. UC of radiation at 1064 nm into blue and green light was obtained. Various emission lines of Tb3+ were observed between 400 and 700 nm due to CET from Yb3+ to Tb3+ ions. A rate equation model was used to describe the temperature dependence of the UC emission intensities and the theoretical results are in good agreement with the experimental data.

Thermally enhanced frequency upconversion in Nd3+-doped fluoroindate glass

Multiphonon assisted frequency upconversion was observed in a Nd3+-doped fluoroindate glass pumped at 866 nm. A near-infrared upconverted emission at 750 nm with a peculiar linear dependence with the laser intensity was observed and explained. The intensity of the upconverted emission experienced a 40-fold enhancement when the sample’s temperature was varied from 298 to 498 K. A rate equation model that includes light pumping and multiphonon absorption via thermally coupled electronic excited states of Nd3+ was used, describing quite well the experimental results.

Optical limiting behavior of bismuth oxide-based glass in the visible range

The authors report experimental results on the optical limiting behavior of a bismuth oxide-based glass by exciting the samples with nanosecond laser pulses at 532 and 598 nm. The results show that two-photon and free-carrier absorption processes contribute for the nonlinear absorption. Values for beta, the two-photon absorption coefficient, and sigma_e, the absorption cross section due to free carriers, were determined. The values for beta and sigma_e are dependent on the amount of bismuth oxide in the glass composition.

Optimization of spectrally flat and broadband single-pump fiber optic parametric amplifiers

Abstract Using well-known theory for fiber optical parametric amplifiers in the no-depletion approximation, a simple condition relating the second- and fourth-order dispersion parameters β 2 and β 4 is demonstrated which ensures ripple-free, broadband gain spectra using realistic fiber parameters. Inclusion of pump depletion gives rise to expressions which enable optimization of fiber length and the maximum achievable ripple-free gain.

Confocal microscopy and spectroscopy of nanocrystals on a high-Q microsphere resonator

We report on experiments where we used a home-made confocal microscope to excite single nanocrystals on a high-Q microsphere resonator. In that way spectra of an individual quantum emitter could be recorded. The Q factor of the microspheres coated with nanocrystals was still up to 10 9 .W e also demonstrate the use of a prism coupler as a well-defined output port to collect the fluorescence of an ensemble of nanocrystals coupled to whispering-gallery modes.

Violet and blue light amplification in Nd3+-doped fluoroindate glasses

We report optical gain at 382 and 414 nm from Nd3+-doped fluroindate glasses after excitation with lasers operating either at 583 or 532 nm. Stimulated emission due to a frequency upconversion process results in increase of the emitted violet and blue light intensity and emission line narrowing. Large optical gain is measured by pump-probe spectroscopy using samples with various Nd3+ concentrations.