Efraín Solarte

Effect of CO2 laser irradiation on the performances of Sol-gel-derived Er3+-activated SiO2 -ZrO2 and SiO2 -HfO2 planar waveguides

Erbium activated SiO2-ZrO2 and SiO2-HfO2 planar waveguides doped with Er3+ ranging from 0.5 to 5 mol% were prepared by sol-gel route using dip-coating deposition on silica glass substrates. All the planar waveguides were optimized in order to confine one propagating mode at 1550 nm. The aim of this work is to present an alternative method for planar optical waveguides processing based on CO2 laser irradiation (wavelength, &lgr;=10.6μm). The effects of pulsed and continuous CO2 laser irradiation on the optical and spectroscopic properties of the waveguides are evaluated and the thermal conventional annealing effect for this system is reported for comparison. X ray diffraction and optical spectroscopy showed that after an adapted pulsed CO2 laser annealing, the resulting materials showed a crystalline environment. An increase of the refractive index of approximately 0.04 at 1.5 μm has been observed on 70SiO2-30HfO2 planar waveguide after continuous CO2 laser annealing. A similar refractive-index variation was detected in all SiO2-ZrO2 planar waveguides after CO2 laser irradiation. We have observed, moreover, that continuous CO2 laser annealing can lead to waveguides with a lower attenuation coefficient: an attenuation coefficient of 0.8 and 1.2 dB/cm @ 632 nm was measured for silica-hafnia and silica-zirconia waveguides respectively, in respect to the attenuation coefficient higher that 2 dB/cm, measured for thermal annealed waveguides. Upon excitation at 514.5 nm continuous-wave laser light, pulsed CO2 irradiated silica-zirconia waveguides show the 4I13/2 -> 4I15/2 emission band with a bandwidth of 12 nm. Before and after conventional thermal annealing, the 4I13/2 level decay curves present a single-exponential profile with a lifetime of 4.0 and 5.7 ms respectively, but the lifetime increases up to 7.0 ms, after pulsed laser annealing treatment.

Glass-ceramics for photonics: Laser material processing

Transparent glass-ceramics, activated by luminescent species, present an important class of photonic materials because their specific optical, spectroscopic and structural properties. Several top-down and bottom-up techniques have been developed for transparent glass ceramic fabrication. Among them, laser material processing plays an important role and many significant results have been obtained in the field of waveguide glass ceramics fabrication. Here, after a short description of the state of art regarding laser material processing for glass ceramics, we report on the specific use of CO2 laser for the fabrication of transparent glass ceramic waveguides.

Lipid Concentration Effects on Light Propagation in Liquid Phantoms

Propagation regime dependence, in lipid liquid phantoms with glycerol as solvent is studied by different lipid concentration using the lateral scattered light distribution. Transition to diffusive transport could be controlled by the lipid density

Coherence measurements of a Nd-YAG laser by image processing of Michelson interferometer fringe patterns

To determine the coherence of a laser device, the concept of visibility is used and applied to the measured interference patterns produced by this laser light in a specific interferometer. In this case, to determine the coherence of a Diode Pumped Solid State Nd -YAG Laser, a digital image processing procedure was developed and applied to the fringe patterns obtained with a rigid arm Michelson interferometer array in order to obtain the coherence function. A spatial filtered laser beam was used to illuminate the interferometer and to produce a circular fringe pattern. The interference pattern was captured on a spatial calibrated translucent screen and photographed by a digital camera. Afterwards, the images were digitally processed to calibrate the pixel distribution and to produce an intensity function from this calibrated image. Data processing of the intensity function values allows to produce the coherence function and to evaluate the coherence degree of the radiation. The interference patterns, intensity distributions and the coherence calculations of the Nd - YAG laser are presented.

Spectroscopic measurements and characterization of soft tissue phantoms

Tissue phantoms are important tools to calibrate and validate light propagation effects, measurements and diagnostic test in real biological soft tissue. We produce low cost phantoms using standard commercial jelly, distillated water, glycerol and a 20% lipid emulsion (Oliclinomel N7-1000 ®) was used in place of the usual Intralipid®. In a previous work we designed a protocol to elaborate high purity phantoms which can be used over months. We produced three different types of phantoms regarding the lipid emulsion – glycerol - gelatin – water composition: Pure gelatin phantoms, lipid in glycerol, and lipid in gelatin phantoms were produced and different concentrations of the lipid emulsion were used to study optical propagation properties of diffusive mixtures. Besides, 1.09 μm poly latex spheres in distilled water were used to produce reference phantoms. In order to use all the phantom sides, the phantoms were produced in disposable spectrometer cuvettes, designed for fluorescence studies. Measurements were performed using an OceanOptics 4000 channels spectrophotometer and integrating spheres. For the scattering measurements a homemade goniometer with a high resolution angular scale was used and the scattering detector was a linear array of optical fibers, with an angular collimator, connected to the spectrophotometer. White LED was used as light source, and the 6328.8 nm HeNe Laser was used for calibration. In this work we present characterization measurements for gelatin and microspheres phantoms using spectral reflectance, diffuse and direct spectral transmittance, and angle scattering measurements. The results of these measurements and their comparison are presented.

Modeling and calculation of light absorption in silicon/metal nanocomposites

Silicon thin films over a glass substrate has been considerate an economical and viable alternative for the photovoltaic industry. Implementation of this technology will contribute to preserve a clean environment helping to reach a sustainable future. Nevertheless, by their own nature, Silicon thin films present small light absorption, and its electrical energy conversion mechanisms, besides their non ideal character, are not completely understood. The inclusions of metal nanoparticles in semiconductors can modify and improve the light absorption properties of these materials by surface plasmon interaction. It is well known that metal nanoparticles, deposited on the surface of Si-Solar cells, improve considerable the efficiency of the cell and it has been shown that there is a strong correlation between the surface plasmon excitation frequency and that of the exciting light. To study the light interactions on such material, we have developed a theoretical model that takes into account the incorporation of metallic nano-particles over Silicon thin films. We have obtained an analytical expression for the effective permittivity of the Semiconductor/Nano-particle system, eff using this result we have analyzed the light absorption process in the case of Silicon with two types of metallic inclusions.

Losses in the fluorescent tracer used in hydrodynamic modeling of constructed wetlands studied by laser induced fluorescence

Fluorescent tracer trials are performed to obtain useful information for hydrodynamic modeling. Particularly they have been used in constructed wetlands, aimed for residual water treatment, in order to find residence time distribution for particles entering the system and, in general, to know the flux pattern. Nevertheless, it has been reported that some tracers, as Rhodamine WT, exhibit adsorption phenomena over the substrate. This situation has to be considered in the analysis of residence time distribution curves, taking into account advection-dispersion processes which are given by the diffusion modified equation. Laser Induced Fluorescence (LIF) with a Nd:YAG laser (532 nm; 35mW), was used to determine Rhodamine WT accumulated concentration. Through adsorption coefficients obtained experimentally, an advection - dispersion model for solute transport in a subsurface flow constructed wetland was evaluated. Including this phenomenon allows to optimize the model, and another important condition is added in the behavior prediction of these complex ecosystems.

Nitrogen detection in the vegetation of prototype constructed wetlands using chlorophyll fluorescence

Constructed wetlands are a very efficient, clean and economical way to remove organic contaminants from waste water. In the whole water cleaning process, some other complex processes, such as physical sedimentation, filtration, chemical precipitation, and material absorption by vegetation, are involved. The Nitrogen absorption efficiency by heliconnia psitacorumm, was studied at laboratory scale in a small reactor simulating a subsurface flow constructed wetland. Chlorophyll increasing was measured by fluorescence, using blue LED, 460 [nm] as excitation light source. Besides, spectral differences were observed in the spectral signal and in its derivative, indicating changes in the plant physiological response.

Chaos Induction in a Laser Diode

Chaos is a class of complex behavior that can emerge from nonlinear dynamical systems, and it exists in both the natural and the technological world. Many biological systems such as the human heart and invertebrate neurons naturally exhibit chaotic behavior. Furthermore, digital computing has made feasible the creation of fractal patterns based on chaos. The beauty of chaos, however, lies not in the aesthetic of fractals, but in the simplicity of the system from which such complex, unpredictable behavior can emerge. The chaotic behavior of a non‐linear R‐L‐Diode circuit has been studied. The non‐linear behavior of the diode was modeled to compare the measured curves with the predicted ones. Period unfolding was observed by feeding the R‐L‐Diode circuit with a sinusoidal signal, varying the frequency and holding constant the amplitude of the input signal. The output voltage was measured on the resistor and bifurcation phenomenon was observed for 2, 4 and 8 periods and for a wide range of frequencies, befor...