Educação matemática pela arte
Gusmão, Lucimar Donizete
2013-08-28
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Current far infrared sources of significant average output power are extremely inefficient, bulb gas lasers which are only line tunable, or require liquid helium cooling and high magnetic fields, for example the p-Ge laser. There is increasing interest in this spectral region for possible security, quality control and gas sensing applications. Electrically pumped multiple quantum well structures would be attractive, but suffer from problems of poor mode overlap with the gain region and free carrier loss from mode overlap with carrier injection and extraction regions. We consider the design of an optically pumped multiple quantum well far infrared laser designed to emit in the one hundred micron region. The spectroscopy and kinetics of these structures, measured on the FELIX free electron laser with picosecond time resolution at the pum...
Glasses based on gallium and lanthanum sulphides (GLS) have attracted considerable interest over the past few years as they have potential for a range of practical applications. These glasses are among a few systems in which lanthanide compounds appear as a constituent; by partly substituting lanthanum with any other rare earth, optical materials with excellent fluorescence properties are readily obtained. The low phonon energy of the sulphide host reduces the non-radiative quenching of electronic levels with small energy separation to the lower levels; radiative transition rates are high because of the very large refractive index (~2.35 at 1.5µm). Thus, optical transitions are available in GLS that are commonly not observed in the conventional oxide glass hosts, enabling new schemes for fibre lasers and optical amplifiers. The high re...
A theoretical study shows that electron population inversion can be realised by optically pumping an asymmetric quantum well (QW) by elegantly designing the subbands. In our previous work, we proposed a three-level system using multiple stepped QWs and a four-level system using multiple coupling QWs to work in the range 40 - 300 µm as an analogue of a far infrared (FIR) gas laser and a Nd3+:YAG laser systems. Research has shown that the gain could be significantly reduced due to hot electron phonon emission and inhomogeneous broadening induced during the QW growth.
Glasses based on gallium and lanthanum sulphides have been investigated because of their properties, such as low phonon energy, high rare-earth solubility and high nonlinearity, which make them attractive for the fabrication of active waveguide devices for photonic applications, such as fibre lasers, amplifiers and all-optical switches (1,2). It is well known that glassy chalcogenides exhibit a number of modifications to their physical properties under the action of light or temperature (3). Reversible photodarkening (PD) is a red-shift of the position of the electronic edge, induced by bandgap or sub-bandgap illumination (4). We have investigated PD in unclad glass fibres with nominal composition 65Ga2S3:32La2S3:3La2O3 (Ga:La:S) and 72.5Ga2S3:27.5La2O3 (Ga:La:S:O) respectively. Both fundamental and practical reasons justify the intere...
We have studied the thermal stability of gratings written in fibres of different composition using a 248 nm KrF excimer laser. Measurements up to ~800 °C confirm the long-term thermal stability of Bragg-gratings written in tin-doped silica fibres and demonstrate a significant advantage over gratings written in conventional photosensitive fibres. Introduction Optical fibre devices have minimal intrusion and considerable advantages in hostile environments, such as in the presence of high electric, magnetic or strong RF fields [1]. Bragg-gratings can be used as a possible transducer for temperature measurements [2], as an alternative to the use of fluorescence emission from rare earth-doped and transition metal-doped fibres [3-41. Bragg-gratings can also be used to measure many other physical parameters including strain [5,6] and pressure...
Gratings written in tin-doped silica fibers by using a 248 nm excimer laser exhibit extremely high thermal stability. Isothermal measurements up to 1100 K demonstrate significant advantages over conventional fiber gratings. Extrapolations from experimental data indicated that gratings operating at 500 K for ten years will retain more than 99% of the initial strength.
Three beam pump-probe measurements in asymmetric stepped quantum wells were conducted using the FELIX free electron laser. We have measured electron intersubband lifetimes of 1.8 ps and 2.5 ps in two GaAs/AlxGa1-xAs stepped quantum well samples. The two samples differ in the total number of quantum wells (80 and 50 periods), donor doping concentrations at the barrier (2 x 1017 cm-3 and 2 x 1018 cm-3) and barrier height (x=0.45 and x=0.35). Experiments were conducted on both samples at temperatures ranging from 4K to room temperature using a liquid Helium cooled cryostat. At saturation pump intensities, however, we observed an absorptive signal of sub-nanosecond lifetime following a normal positive transmissive signal of the order of picosecond lifetime. This slow decay absorptive signal is relatively stronger in intensity than the posi...
A technique for the remote inspection and monitoring of partial discharge (PD) activity using an optical network is described. The network uses a LiNbO3 modulator to modulate the intensity of the transmitted light approximately proportional to the voltage applied across the modulator. The laser light is transmitted along an optical fibre and measured remotely by a high-speed optical receiver. A capacitive coupler has been used to detect partial discharge activity and act as the modulator's input voltage source. The electro-optic modulator is passive and does not require a power supply at the site of the PD detection sensor. The system has the additional advantages of being immune to electromagenetic interference, having very little signal transmission attenuation, with good sensitivity, compact size, as well as being convenient and saf...
The fluorescence properties of thiazole orange, linked via a (1) hydrophobic alkyl or a (2) hydrophillic ethylene glycol chain to the central internucleotidic phosphate group of a pentadeca-2'-deoxyriboadenylate (dA(15)), are evaluated. Linkage at the phosphate group yields two stereoisomers, S-isomer of the phosphorus chiral center (Sp) and R-isomer of the phosphorus chiral center (Rp); these are studied separately. The character of the linkage chain and the chirality of the internucleotidic phosphate linkage site influence the fluorescent properties of these thiazole orange-oligonucleotide conjugates (TO-probes). Quantum yields of fluorescence (Phi(fl)) of between 0.04 and 0.07 were determined for the single-stranded conjugates. The fluorescence yield increased by up to five times upon hybridization with the complementary sequence (d...
We demonstrate that ultrabroadband ultrashort-pulse white light supercontina can be used to track the group velocity of photons in optical waveguides using a Kerr gate technique. Results on silicon nitride slab waveguides show both polarization birefringence and multimode dispersion, which vanish at critical wavelengths. When photonic crystals are embedded in the waveguides, the higher order modes are excited within the band-gap region, demonstrating the need to control their dispersion to make effective use of photonic crystal waveguide devices.
