Eduardo Cotta | Universidade Federal do Amazonas (original) (raw)

Papers by Eduardo Cotta

Scanning, 2015

Leaves surfaces have various structures with specific functions and contribute to the relationshi... more Leaves surfaces have various structures with specific functions and contribute to the relationship with the environment. On morphological studies are analyzed various parameters, ranging from macro scale through the micro scale to the nanometer scale, which contribute to the study of taxonomy, pharmacognosy, and ecology, among others. Functional structures found in leaves are responsible for the wide variety of surfaces and some behaviors are given in terms of cellular adaptation and the presence or absence of wax. This study reports the characterization of Anacardium occidentale L. leaf surface and the techniques used therein. A set of scanning electron microscope (SEM) and atomic force microscope (AFM) images performed on fresh leaf allowed observation of textured and heterogeneous profiles on both sides. SCANNING 9999:1-7, 2015. © 2015 Wiley Periodicals, Inc.

2007 European Conference on Lasers and Electro-Optics and the International Quantum Electronics Conference, 2007

Page 1. Polariton laser Instability behavior in a GaAs microcavity Eduardo A. Cotta, Franklin M. ... more Page 1. Polariton laser Instability behavior in a GaAs microcavity Eduardo A. Cotta, Franklin M. Matinaga Federal University of Minas Gerais, Brazil matinaga@fisica.ufmg.br ... References 1) SLMcCall et al, Am. Phys. Soc, 20 (1975) 636. 2) A. Baas et al, Phsy. Rev. ...

2013 IEEE Congress on Evolutionary Computation, 2013

ABSTRACT In this paper we present the first quantitative study of parameters optimization for sem... more ABSTRACT In this paper we present the first quantitative study of parameters optimization for semiconductor microcavities synthesis under uncertainty using genetic algorithm. A microcavity is a system in which a gain medium can interact with a single cavity mode. These structures have been used in important studies of several areas for technological or purely scientific purposes. However, the definition of the optimal parameters for the fabrication of microcavities is a difficult task. Moreover, the difficulty further increases during the growth process due to experimental uncertainties that may occur, mainly related to the thickness of the layers. Thus, the device can present different properties from those desired. Based on the reflectance spectra of a AlxGa1-xAs semiconductor microcavity, our goal is to find the optimal parameter set (aluminum concentrations x, thickness of layers and the number of layers). This set of parameters may offer increased robustness in the growth process, while providing a considerable Quality Factor and the desired position of the cavity resonance. The results indicate that the proposed algorithm is able to find satisfactory solutions, minimizing the problems caused by inaccuracy in the growth of these devices.

IEEE Transactions on Circuits and Systems I: Regular Papers, 2014

ABSTRACT The three FET CMOS active pixel sensors (APS) operating in the linear-logarithmic mode i... more ABSTRACT The three FET CMOS active pixel sensors (APS) operating in the linear-logarithmic mode is one of the most efficient wide-dynamic-range imagers. However, the quality of the image generated at the focal-plane array is often compromised by fixed-pattern noise (FPN) between pixels. The classical correlated double sampling (CDS) technique is used to reduce FPN in imagers operating in the linear mode. But in the complementary linear-logarithmic mode CDS does not work properly and alternative techniques must be applied to reduce FPN. The ordinary alternative techniques increase either the complexity of the pixel or its external circuitry. In order to avoid these problems a new technique was devised to reduce FPN that can be applied to the basic three FET APS architecture. With the purpose to assert the efficacy of the proposed technique a small array was fabricated in a standard 0.35 murmmmu{rm m}murmm CMOS technology. Experimental results show that the proposed technique is able to reduce FPN quite steadily within the whole illumination range used to test the array. And therefore, the signal-to-noise-and-distortion ratio (SNDR) of the array is also improved within the whole range of operation.

physica status solidi (c), 2007

Biexciton emission properties were studied in a single GaAs quantum well semiconductor planar mic... more Biexciton emission properties were studied in a single GaAs quantum well semiconductor planar microcavity by photoluminescence measurements at low temperatures. At high pump intensity a bipolariton emission appears close to the lower polariton mode. This new mode appears when we detune the cavity resonance out of the lower polariton branch, showing a laser like behavior. Very small lines widths were measured, lying below 110 µeV and 150 µeV for polariton and bipolariton emission respectively. The input/output power (I/O) measurements show that the bipolariton emission has a weaker coupling efficiency compared to previous results for polariton emission. Simultaneous photoluminescence and near field measurements show that the polariton and bipolariton emission are spectrally and spatially separated.

The European Physical Journal B, 2013

Brazilian Journal of Physics, 2004

Coherent emission efficiency in a 100Å GaAs SQW microcavity was enhanced one order when pumped re... more Coherent emission efficiency in a 100Å GaAs SQW microcavity was enhanced one order when pumped resonantly at 10 K, compared to the off-resonant excitation. The usual kink observed in the exciton emission linewidth as well as in the emission intensity in relation to the pump power, changes smoothly instead of the usual abrupt kink observed in the off-resonant microcavity laser. In addition, polarization measurements show a correlation relationship between the pump light polarization and the cavity emission polarization.

Physical Review B, 2007

We report an experimental observation of polaritonic optical bistability of the laser emission in... more We report an experimental observation of polaritonic optical bistability of the laser emission in a planar semiconductor microcavity with a 100Å GaAs single quantum well in the strong-coupling regime. The bistability curves show crossings that indicate a competition between a Kerr-like effect induced by the polariton population and thermal effects. Associated with the bistability, laser-like emission occurs at the bare cavity mode.