Local density of electromagnetic states within a nanometric gap formed between two thin films supporting surface phonon polaritons

We present a detailed physical analysis of the near-field thermal radiation spectrum emitted by a silicon carbide (SiC) film when another nonemitting SiC layer is brought in close proximity. This is accomplished via the calculation of the local density of electromagnetic states (LDOS) within the gap formed between the two thin films. An analytical expression for the LDOS is derived, showing explicitly that (i) surface phonon polariton (SPhP) coupling between the layers leads to four resonant modes, and (ii) near-field thermal radiation emission is enhanced due to the presence of the nonemitting film. We study the impact of the interfilm separation gap, the distance where the fields are calculated, and the thickness of the nonemitting layer on the spectral distribution of the LDOS. Results show that for an interfilm gap of 10 nm, the near-field spectrum emitted around the SPhP resonance can increase more than an order of magnitude as compared to a single emitting thin layer. Interfilm SPhP coupling also induces a loss of spectral coherence of resonance, mostly affecting the low frequency modes. The effect of the nonemitting film can be observed on LDOS profiles when the distance where the fields are calculated is close to the interfilm gap. As the LDOS is calculated closer to the emitter, the near-field spectrum is dominated by SPhPs with small penetration depths that do not couple with the modes associated with the nonemitting film, such that thermal emission is similar to what is observed for a single emitting layer. Spectral distribution of LDOS is also significantly modified by varying the thickness of the nonemitting film relative to the thickness of the emitting layer, due to an increasing mismatch between the cross-coupled SPhP modes. The results presented here show clearly that the resonant modes of thermal emission by a polar crystal can be enhanced and tuned, between the transverse and longitudinal optical phonon frequencies, by simply varying the structure of the system. This analysis provides the physical grounds to tune near-field thermal radiation emission via multilayered structures, which can find application in nanoscale-gap thermophotovoltaic power generation.publisher versio

Small dielectric spheres with high Refractive index as new multifunctional elements for optical devices

The future of ultra-fast optical communication systems is inevitably connected with progress in optical circuits and nanoantennas. One of the key points of this progress is the creation of elementary components of optical devices with scattering diagrams tailored for redirecting the incident light in a desired manner. Here we demonstrate theoretically and experimentally that a small, simple, spatially homogeneous dielectric subwavelength sphere with a high refractive index and low losses (as some semiconductors in the visible or near infrared region) exhibits properties allowing to utilize it as a new multifunctional element for the mentioned devices. This can be achieved by taking advantage of the coherent effects between dipolar and multipolar modes, which produce anomalous scattering effects. The effects open a new way to control the directionality of the scattered light. The directional tuning can be obtained in a practical way just by a change in the frequency of the incident wave, and/or by a well-chosen diameter of the sphere. Dielectric nanoparticles with the required optical properties in the VIS-NIR may be now readily fabricated. These particles could be an efficient alternative to the widely discussed scattering units with a more complicated design.This research was partly supported by MICINN (Spanish Ministry of Science and Innovation) through project FIS2013-45854-P and by the Ministry of Education and Science of Russian Federation through grant 14.Z50.31.0034

The Euclid mission design

Euclid is a space-based optical/near-infrared survey mission of the European Space Agency (ESA) to investigate the nature of dark energy, dark matter and gravity by observing the geometry of the Universe and on the formation of structures over cosmological timescales. Euclid will use two probes of the signature of dark matter and energy: Weak gravitational Lensing, which requires the measurement of the shape and photometric redshifts of distant galaxies, and Galaxy Clustering, based on the measurement of the 3-dimensional distribution of galaxies through their spectroscopic redshifts. The mission is scheduled for launch in 2020 and is designed for 6 years of nominal survey operations. The Euclid Spacecraft is composed of a Service Module and a Payload Module. The Service Module comprises all the conventional spacecraft subsystems, the instruments warm electronics units, the sun shield and the solar arrays. In particular the Service Module provides the extremely challenging pointing accuracy required by the scientific objectives. The Payload Module consists of a 1.2 m three-mirror Korsch type telescope and of two instruments, the visible imager and the near-infrared spectro-photometer, both covering a large common field-of-view enabling to survey more than 35% of the entire sky. All sensor data are downlinked using K-band transmission and processed by a dedicated ground segment for science data processing. The Euclid data and catalogues will be made available to the public at the ESA Science Data Centre

The Multi-Spectral Reordering (MSR) technique for the narrow band modeling of the radiative properties of nonuniform gaseous paths: the correlated/uncorrelated approximations

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Optimizations of photovoltaic cells including the minimization of internal heat sources

International audienceA new approach is introduced and illustrated for optimizing the performances of photovoltaic cells. A thermal criterion, the minimization of the internal heat sources, is added to the usual criteria that consist of minimizing the optical and electrical losses. A proof of concept is delivered by means of modeling in the case of a standard crystalline silicon (cSi) cell for which the dependence on temperature of optical, electrical, and thermal properties is well known. A numerical code named TASC-1D-cSi simulating the optical-radiative, electrical, and thermal behaviors of cSi solar cells is used. Besides the current-voltage characteristics, this simulation tool provides the spectral variations of the thermalization, recombination, and radiative internal heat sources as well as the equilibrium temperature of the cell which depends on the outdoor conditions. The cell or the anti-reflection coating thickness is varied while the other parameters are prescribed. It is demonstrated in given outdoor conditions that considering the minimization of the internal total heat source in addition to the minimization of the optical and electrical losses modifies significantly the value of each of these parameters that maximizes the output power of the cell. For example, in a thermal condition with natural convection at the front and insulation at the back of the cell, the optimum cell thickness is found to be 55 μm and the optimum antireflection coating thickness 87 nm, instead of, respectively, 75 μm and 80 nm when the cell is maintained at 25 °C. These results suggest that a thermal design rule involving the internal heat source might be included in the improvement of solar cells at use and in the development of the next generation photovoltaics

A full thermal model for photovoltaic devices

International audienc

Optimization of solar thermophotovoltaic systems including the thermal balance

International audienc

Thermal and Electrical Behaviors of Silicon Photovoltaic Cells with Antireflection Layers

International audienc

Numerical simulation of a vertical solar collector integrated in building frame: radiation and turbulent natural convection coupling

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