Ardi Loot

Angular shaping of fluorescence from synthetic opal-based photonic crystal

Spectral, angular, and temporal distributions of fluorescence as well as specular reflection were investigated for silica-based artificial opals. Periodic arrangement of nanosized silica globules in the opal causes a specific dip in the defect-related fluorescence spectra and a peak in the reflectance spectrum. The spectral position of the dip coincides with the photonic stop band. The latter is dependent on the size of silica globules and the angle of observation. The spectral shape and intensity of defect-related fluorescence can be controlled by variation of detection angle. Fluorescence intensity increases up to two times at the edges of the spectral dip. Partial photobleaching of fluorescence was observed. Photonic origin of the observed effects is discussed.

Goniometric Setup for Plasmonic Measurements and Characterization of Optical Coatings

Fundamentals of light-induced surface plasmon-polariton waves are considered and implemented on the example of goniometric setup assembled by the authors. The setup was used for investigation of angular dependent light transmittance, reflectance, and fluorescence in dielectric layer containing chromophores. It is explained how optical characteristics of multilayered coatings (thicknesses, refractive indices, and surface roughness) can be deduced from the properties of transmitted and reflected light. Original data about attenuated total internal reflection and plasmon-coupled rare earth fluorescence were obtained. Particularly, angular spectral dispersion and control of Sm3+ fluorescent bands were demonstrated.

Counterintuitive increase in optical scattering efficiency during negentropic orientational transition in dilute ZnO nanowire suspensions

We demonstrate experimentally that the electrophoretic manipulation of a ZnO nanowire (NW) suspension in polydimethylsiloxane (PDMS) causes a remarkable change in optical scattering. Counterintuitively, as an electric field is applied to the suspension and a negentropic orientational transition from a chaotically oriented state to a partially ordered (aligned) state is induced, the geometrical cross-section of the particles decreases whereas the scattering efficiency increases significantly, indicating an increase in the scattering cross-section. The alignment of the longer axis of oblong ZnO nanoparticles in the direction of incident light unexpectedly resulted in up to a 40% decrease in transmittance in the middle of the visible spectral range in the case of 150 μm thick composite films with below 0.1 vol% NW concentration. A prepared prototype smart window device exhibited spontaneous restoration of transmittance, persistent electro-optical performance (0% change in contrast after more than 10 cycles), and temporal stability against nanoparticle sedimentation and agglomeration.

Fluorescence of TiO2:Sm3+ composite stimulated by plasmon waves

Plasmon-coupled fluorescence of rare earth Sm3+ ions doped into the TiO2 film placed on thin gold layer is investigated. It was demonstrated that plasmon waves induced in the gold layer strongly influence rare earth emission. We revealed that each spectral peak of Sm3+ emission can be directionally separated, polarized and enhanced by intensity due to coupling with plasmon waves propagating in the gold film. It is noticeable that we obtained about 10 % of non-linear growth in Sm3+ emission intensity over the pumping strength.

Steps toward the experimental realization of surface plasmon polariton enhanced spontaneous parametric down-conversion

Abstract The realization of efficient and miniature source of entangled photon pairs stills remains a challenge. In this work, we experimentally studied the possibility to enhance the process of spontaneous parametric down-conversion by surface plasmon polaritons. The details of the experimental setup will be discussed along with theoretical calculations of the enhancement factor.

Enhanced Dynamical Casimir Effect for Surface Plasmon Polaritons and Guided Dielectric Waves

Dynamical Casimir effect - emission of surface waves due to oscillations of optical length of resonator under laser excitation is considered. If amplitude of oscillations coincides with wavelength of emission then its strong enhancement takes place.

Scale-Dependent and Seasonal Performance of SILAM Model in Estonia

The SILAM model is running in Finnish Meteorological Institute (FMI) for European air quality forecasts (http://silam.fmi.fi). The 7 km resolution of both TNO-MACC emission grid and Nordic model domain is too coarse for urban and industrial areas. The Estonian modelling domain, operated jointly by the University of Tartu and Estonian Meteorological and Hydrological Institute (http://meteo.physic.ut.ee/silam, resolution 3.3 km) includes the Baltic countries and southern Finland. In this study the database of pollution sources on the territory of Estonia is refined and performance of SILAM with the new database is studied. The new database presents better spatial distribution, differences in yearly emission budgets should be looked into in further studies. Average concentrations of NOx, SO2 and particulate matter are reproduced rather well, NOx underestimated slightly and particulate matter significantly. The new database shows an improvement in hourly and daily correlations, especially for urban stations.

Atmospheric transport model applied to understand the effect of biogenic emissions to secondary atmospheric aerosol in hemiboreal zone

The SILAM model with built-in isoprene and monoterpene emission module from natural sources was run for May to August 2006 in Baltic Sea region. In this study VOCs were advected as passive tracers. Modelled hourly VOC-tracer concentrations were compared with sub-half-micrometre aerosol concentrations, simultaneously measured in Preila (Lithuania), Tahkuse (Estonia), Hyytiala (southern Finland) and Varrio (northern Finland). Linear correlation coefficients between measured and modelled concentrations were found in range 0.45 to 0.72. Bilinear regression result, based on summary monoterpenes and sulphate (AQME II model run, FMI), is even better correlated with aerosol: coefficients from 0.58 to 0.83. Thus, biogenic VOCs and sulphates are likely two major contributors to the sub-half-micron aerosol in the Nordic-Baltic region. This study demonstrates that a state-of-art advection-diffusion model with proper emission database is capable to predict the accumulation mode aerosol concentrations in the atmosphere. More research in aerosol dynamics is needed to refine the results.

A Wintertime Local-to-Regional Scale Test Case Study of SILAM Model

The SILAM model (version 4.5.4) is applied for retrospective modelling of wintertime deposition fluxes of fly ash and sulphate near Estonian oil-shale-based industrial complex. The fluxes are validated against snow-based deposition measurements that have been carried out during nine winters since 1985. Also, the data from the Lahemaa (Estonia) and Virolahti (Finland) EMEP stations are applied for regional-scale validation. In this test case SILAM tends to systematically underestimate the deposition of fly ash and overestimate the deposition of sulphate at distances up to 30 km from the pollution sources. Overestimation of sulphate is severe during recent decade, whereas at more remote (100 km) EMEP stations the fluxes are nearly correct. As SILAM is basically developed and validated for meso-scale applications, some scale-dependent effects near the sources may appear. The recent changes in oil shale combustion technology may also play a role in increasing overestimation trend for sulphate.