Photon management with nanostructures on concentrator solar cells

Optimizing the feature sizes of dielectric nanostructures on the top (ZnS) and bottom (SiO2) surfaces of a 1 μm thick GaAs solar cell, we obtain a higher efficiency (34.4%) than a similar cell with a state of the art bilayer antireflection coating and a planar mirror (33.2%). The back side nanostructure increases the photocurrent due to enhanced optical path length inside the semiconductor, while the nanostructure on the front side increases the photocurrent due to lower reflectance losses. © 2013 AIP Publishing LLC.We acknowledge the SGAI-CSIC for the allocation of computational resource and the financial support by MINECO (ENE2012-37804-C02-02, FPI grant) and CAM (S2009/ENE-1477).Peer Reviewe

Photonics Crystals on high efficiency III-V Solar Cells

Póster presentado en la 28th European PV Solar Energy Conference and Exhibition (EU PVSEC 2013), celebrada en París del 30 de septiembre al 4 de octubre de 2013.We have explored the following photon management options for increasing the efficiency of concentrator solar cells: increasing the voltage by recycling the luminescence, increasing the current reducing reflection and increasing the optical path. We find that a 1m m thick GaAs solar cell with optimized nanostructured front and back surfaces has significantly higher efficiency than a similar cell with a perfect back side mirror and a state of the art bilayer antireflective coating. We have also designed a multilayer coating with high reflectivity at angles away from the surface normal that results in luminescence trapping, and thus increases the open circuit voltage and the cell efficiency.Peer Reviewe

Fotopletismografía laparoscópica: Nueva técnica mínimamente invasiva y estudios experimentales iniciales

In the endoscopic procedures there is not possible to use the sense of touch for the detection of weak palpitations as in open surgery, neither to directly evaluate the oxygenation and perfusion of intra-corporeal organs and tissues. Here, we present the initial results after the application of laparoscopic photoplethysmography, a novel technique developed by our group, which allows obtaining specific clinical parameters and overcome the cited drawbacks. From the photoplethysmograpic signals of different wavelengths recorded in intra-abdominal organs and territories of animal models, their pulse values and oxygenation related quotients have been derived. © Sociedad Española de Óptica.Este trabajo ha sido financiado por el proyecto PI 04/0715 del Fondo de Investigaciones Sanitarias. Agradecemos la colaboración prestada durante el estudio experimental por Dr. José Carlos Manuel Palazuelos, Dr. Juan Carlos González Cueli y las diplomadas en Enfermería del CENDOS. Parte de los resultados aquí expuestos han sido presentados oralmente en el Congreso de la Sociedad Española de Laparoscopia (SECLA 2009) celebrado en Santander en mayo de 2009. SMLS está contratada por el Programa I3P con financiación del Fondo Social Europeo.Peer Reviewe

Plasmonic antenna hybrids for active control in the near and midinfrared

Resumen del trabajo presentado a la Spanish Conference on Nanophotonics (Conferencia Española de Nanofotónica-CEN), celebrada en Donostia-San Sebastián (España) del 3 al 5 de octubre de 2018.Hybrid platforms combining metallic plasmonic nanoantennas (NAs) and materials with interesting properties as phase-change or spintronics offer excellent technological opportunities for active plasmonics, as they can provide large changes in their optical response. In this talk I will demostrate first how gold NAs grown on vanadium dioxie (VO2), characterized by a reversible insulator-to-metal transition (IMT) at around 68ºC, can improve the performance of this material by providing an efficient enhancement mechanism for both the optically induced excitation and readout. Using picosecond laser pulses a highly localized phase transition is driven in nanoscale regions around the NAs. These antennas-VO2 hybrid solutions provide a conceptual framework to merge field localization and phase transition enabling nanoscale optical memory functionalities. In the second part I will show how the combination of Au microantenna arrays with a Ni81Fe19/Au multilayer supports provide metamaterial platforms with new functionalities. In this case, the plasmon resonance sustained by the NAs alliate with the GMR and MRE effects of the multilayer to allow low magnetic-field controlled modulation in the mid-infrared, where light modulation is very challenging. This approach establishes a roadmap for spintronically-controlled devices in the whole mid-IR to THz band.Peer Reviewe

Near-infrared transmittance pulse oximetry with laser diodes

Pulse oximeters are widely used for noninvasive monitoring of oxygen saturation in arterial blood hemoglobin. We present a transmittance pulse oximetry system based on near-infrared (NIR) laser diodes (750 and 850 nm) for monitoring oxygen saturation of arterial blood hemoglobin. The pulse oximetry system is made up of the optical sensor, sensor electronics, and processing block. Also, we show experimental results obtained during the development of the whole NIR transmittance pulse oximetry system along with modifications in the sensor configuration, signal processing algorithm, and calibration procedure. Issues concerning wavelength selection and its implications for the improvement of the transmittance pulse oximetry technique are discussed. The results obtained demonstrate the proposed system’s usefulness in monitoring a wide range of oxygen saturation levelsSMLS is supported by Programa Ramo´n y Cajal from the Spanish Ministry of Science and Technology.Peer reviewe

Analysis of local deformations in heterostructures containing short period superlattices by high-resolution transmission electron microscopy

This work describes the application of the Lattice Fringe Spacing Measurement (LFSM) method to the study of complex multiquantum well heterostructures containing both low-misfit and strain compensated short period superlattices in barriers and wells, respectively. 90º-wedge cross-sectional samples have been used. The adequate choice of both experimental conditions and digitized sampling allows the whole heterostructure to be visualized and studied in a single High Resolution Transmission Electron Microscopy (HRTEM) image. Sample preparation and image processing technique are simple and inexpensive, resulting a fast procedure particularly suited for the analysis of large areas. By this way, in a single HRTEM image we have measured, in the growth direction, the lattice spacings at either side of the multiple grown interfaces as well as the period variations of both types of superlattices; in addition, we have measure on the same image the lattice strain in a direction perpendicular to the growth direction by using the LFSM and the Cumulative Sum methods. We have observed local lateral variations within the wells, with regions tensile or compressively strained, while a vestige of the grown SL remains, indicating the occurrence of a strain induced lateral composition modulation process spontaneously produced during the growth of strain compensated short-period superlattices. This is further confirmed in cross-section prepared by the tripod mechanical polisher method.The authors express their sincere thanks to A. Guerrero for his support in the CUSUM program, to J. Thibault who invited them to take benefit of the 4000EX microscope available in the CEN-Grenoble, and to A. Sanz-Hervás, from Depto. Tecnología Electrónica, E.T.S.I.T.-U.P.M., Madrid, for his support in XRD measurements.Peer reviewe

Fotopletismografía con diodos láser infrarrojos en órganos intraperitoneales del cerdo

Entre las técnicas que se emplean para monitorizar órganos y tejidos se encuentran la fotopletismografía, la oximetría de pulso y la flujometría por efecto Doppler láser. Existen procesos que afectan a determinados órganos o territorios del organismo, sin repercusión significativa en el grado de oxigenación periférica, que no pueden ser monitorizados con los dispositivos disponibles actualmente. Resulta necesario desarrollar métodos y técnicas de oximetría que permitan la determinación "in situ" del grado de oxigenación tisular de diversos territorios intracorpóreos. En el presente trabajo se exponen los resultados preliminares del estudio de órganos intraperitoneales de un cerdo durante una intervención quirúrgica utilizando un sistema basado en dos diodos láser infrarrojos previamente desarrollado. Se han registrado los fotopletismogramas por transmisión a 750 nm y 850 nm en la aorta, la pared gástrica y el mesocolon. Es imprescindible modificar la geometría del sensor empleado y diseñar sensores optimizados para monitorizar diferentes órganos de interés.Este trabajo ha sido financiado por la Asociación Cántabra de Cirugía y el proyecto CICYT TIC98-1025. S.M. López Silva es investigadora del Programa Ramón y Cajal del Ministerio de Ciencia y Tecnología.Peer reviewe

Optical characterization of disordered InxGa12xP alloys

3 páginas, 4 figuras.We present results on the optical characterization of InxGa1−xP layers grown by atomic layer molecular beam epitaxy on GaAs (001) substrates at a growth temperature of 420 °C. Our results show that the optical characteristics of these layers, which do not show ordering effects, are strongly dependent on surface stoichiometry during growth. In this way, we can obtain either highly homogeneous alloys with a predictable band-gap energy or layers with optical properties indicative of spatial localization effects, like an anomalous behavior of photoluminescence peak energy with temperature and a large shift between the emission energy and absorption edge.The authors wish to acknowledge the Spanish ‘‘CICYT’’ for financial support under Project No. TIC96- 1020. Thanks are also due to the Spanish–French Bilateral Program under Grant No. HF1995-0028.Peer reviewe

On laparoscopic photoplethysmography and pulse oximetry

Here we comment on the paper entitled >A novel laparoscopic pulse oximeter device. An easy, efficient and cost-effective way of detecting arterial structures.> authored by Theodosopoulos et al., and recently published in the April issue of the Journal of Clinical Monitoring and Computing. © Springer 2010.Peer Reviewe

Photoluminescence characterization of GaAs quantum well laser structure with AlAs/GaAs superlattices waveguide

Dependence on the excitation power and temperature of the photoluminescence emission of GaAs quantum well laser structures using GaAs/AlAs superlattices in the waveguide is reported. The effects related to a quality reduction due to the presence of a thick ternary AlGaAs cladding layer in the bottom of the laser structure were elucidated by comparing to the photoluminescence of a similar waveguide structure, except for the AlGaAs bottom layer. The excitation power dependence shows the strong excitonic origin of the light emission in the temperature range 4-300 K in both structures. Carrier transport mechanisms through the superlattices is analyzed from the evolution of the photoluminescence of the quantum well and the superlattice confining layers; a structure dependent transparency temperature is defined, at which transport changes from tunneling assisted to extended minibands regime. The value of this parameter depends on the localized states in the superlattice minibands, caused by interface roughness.Peer Reviewe