Showing papers by "Abraham Katzir published in 1997"

The luminescence properties of Dy-doped high silicate glass

Abstract: The visible luminescence of silicate glass (SiO2 (> 70%)—R2O3[B2O3, Al2O3]—RO[ZnO, MgO, CaO, BaO]—R2O[Na2O, K2O]) doped with various concentrations of dysprosium was investigated The emission, excitation and absorption spectra, as well as kinetic parameters, were measured over a temperature range from 20 to 300 K The Judd—Ofelt analysis was applied to the data, in order to calculate transition rates and branching ratios for all observed emission bands Concentration quenching was experimentally observed at a Dy ion concentration higher than 8 × 1019 cm−3 and explained by an analytical model based on the Inokuti-Hirayama theory The quantum efficiency of visible luminescence and the stimulated emission cross-section at 570 nm were (85 ± 50% and (34 ± 04) × 10−21 cm2, respectively

Towards a remote IR fiber-optic sensor system for the determination of chlorinated hydrocarbons in water

Abstract: A laboratory prototype of a mid-infrared (MIR) fiber-optic sensor system capable of remote on-site and real-time determination of chlorinated hydrocarbons (CHCs) in water has been developed. The system is based upon fiber evanescent-wave spectroscopy (FEWS) and consists of silver halide fibers that are coupled to a portable Fourier transform infrared (FTIR) spectrometer. These fibers serve both as signal transfer lines and as sensing elements. In the latter case they are coated with thin films of ethylene/propylene copolymer for the purposes of enrichment of the analytes and exclusion of water. A detection limit for tetrachloroethylene of 300 ppb has been achieved with a total contact time between sample and sensor of 10 min.

Mechanical and optical properties of silver-halide infrared transmitting fibers

Abstract: This article presents a review of the optical and mechanical properties of infrared transmitting fibers extruded from single crystals of silver-halides at the Applied Physics Group in Tel-Aviv University during the last decade. The optical properties of AgclxBr1-x crystals and fibers include the spectral transmission window, laser power transmission, the change of the power distribution traveling along the fiber, and the laser-induced breakdown. The mechanical properties include the investigation of the ultimate tensile strength (UTS), hardness, and the elastic strain limits of these fibers and their composition dependence. The mechanical properties that involve single and multiple bending of fibers in the plastic and the elastic strain limits are also described.

Blood diagnostics using fiberoptic evanescent wave spectroscopy and neural networks analysis

Abstract: A spectral analysis of human blood serum was undertaken by fiberoptic evanescent wave spectroscopy (FEWS) using a Fourier transform infrared (FTIR) spectrometer. The blood serum samples were introduced into a special cell designed for FEWS of liquids, with an IR transmitting silver halide fiber as the sensing element. The spectra were analyzed by models of neural networks (NN), and the concentrations of protein, cholesterol and uric acid in human blood serum were obtained. Our results are in agreement with those obtained by ordinary chemical enzymatic methods and multivariate calibration methods. The estimated prediction errors obtained (in percent of the average value) were 4.7% for total protein, 22% for cholesterol and 35% for uric acid. This method can be used for in-situ real-time blood analysis.

Temperature-controlled CO 2 laser tissue welding of ocular tissues

Abstract: Laser has been used experimentally for bonding of tissues. The probable advantages of this method are being non-contact, no foreign materials are introduce and it is fast. Previous works have shown laser welding to be an effective way for connecting blood vessels', peripheral nerves2, bowl segments3 and many other biological tissues. In ophthalmology, previous attempts to weld corneal tissue using CO2 lasers have failed4'5.

Silver-halide fiber tip as a beam homogenizer for infrared hollow waveguides.

Abstract: A beam-homogenizing device consisting of a short tip of silver-halide infrared fiber eliminates the low-order multimode effect generated by bending of hollow guides. A series of experiments with a CO(2) laser shows that the solid fiber functions as a homogenizer with a small insertion loss of 0.2dB.

Temperature measurements using pulsed photothermal radiometry and silver halide infrared optical fibers

Abstract: A novel technique for measuring temperature, based on pulsed photothermal radiometry and analysis of the spectral and temperature dependence of Planck’s blackbody equation, is described. In this technique a body is irradiated by a laser pulse and its temperature inferred from the time dependence of the emitted infrared signal curve. This technique was used for near ambient temperature measurements using a CO2 laser, an infrared detector, and infrared transmitting silver halide optical fibers. The experimental results are consistent with theory. This technique is independent of changes in emissivity or geometric factors and it will be useful for accurate and fast noncontact temperature measurements.

Optimizing the modulation for evanescent-wave analysis with laser diodes (EWALD) for monitoring chlorinated hydrocarbons in water

Abstract: Fiber evanescent-field analysis (FEFA) is a novel and promising sensor technique for on-line and in situ analysis of hydrocarbons in water. With a conventional IR light source and FTIR spectroscopy it allows multicomponent analysis, while the use of mid-infrared (MIR) tunable diode lasers (TDLs) results in sensitive and selective single-component analysis. A new modulation technique operates the diodes with short pulses in combination with base-current modulation. Conventionally these lasers are used for trace-gas analysis with spectral features of 10 −6 spectral resolution. For the new evanescent-wave analysis with laser diodes (EWALD) sensor application, broadband spectra must be scanned, which does not allow high-resolution techniques to be used. The laser emission bandwidth does not need to be small, 10 −3 to 10 −4 resolution is sufficient, but the wavelength scan range must be about 10 −2 . In short-pulse mode, this can be achieved; furthermore, the laser can be used at higher operation temperature for more convenient application. The laser modulation characteristics are dependent on operation temperature, base-current, and pulse-current width and amplitude. The influence of these parameters and their optimization will be discussed.

Optimized sensitive coatings for MIR fiber optic sensors

Abstract: In this study, novel coating materials for MIR fiber-optic sensors have been investigated, in order to assess the possibilities and limitations associated with introducing materials of higher molecular complexity as coating materialsTwo materials—poly(acrylonitrile-co-butadiene) and poly(styrene-co-butadiene)—could be found that show increasedsorption coefficients for substances such as chlorinated phenols and anilines together with only moderately narrowedspectral windows Keywords: JR fiber-optic sensors, selectivity, new coating materials 1 INTRODUCTION For mid-infrared (MIR) fiber-optic sensors—like for almost any other chemical sensor system—the chemically sensitivelayer attached to the surface of the optical transducer plays a central role However, in most other chemical sensors this layer is the only component which introduces chemical selectivity and the ability to discriminate between differentanalytes In case of MIR sensors the necessary selectivity is mainly contributed by the physical transducer—IRspectrometry—itseif, while the tasks of the sensor coating are mainly enrichment of the analytes of interest near thesurface of the waveguide, suppression of interfering background absorption (eg due to water) and protection of thewaveguide1 As a consequence, coating materials investigated so far were mostly simple aliphatic polymers, whichshow low sorption coefficients for water and good enrichment properties for apolar substances such as chlorinated

Effects of thermal treatment on the infrared transmission of polycrystalline silver halide fibers.

Abstract: Polycrystalline silver halide fibers were thermally treated by a variety of heating and quenching procedures. For each procedure, the recrystallization process and the grain-size distribution were investigated. The absorption and scattering coefficients at 10.6 µm and the infrared transmittance spectra in the 3–20 µm wavelength range were also measured. Treatment at temperatures above 170 °C and long time intervals generally lead to an increase in grain size, with a dependent increase in absorption and scattering coefficients at 10.6 µm. Heating only to temperatures below 170 °C reduced the absorptive and scattering losses. The Rayleigh–Gans scattering model was utilized to describe the scattering behavior. A model involving cation vacancies localized at charged dislocations or casual divalent impurities is suggested to explain the infrared absorption of the fibers.

Luminescence properties of praseodymium- and erbium-doped silver bromide crystals.

Abstract: The luminescence of silver bromide crystals doped with praseodymium and erbium ions was investigated over the visible and near-infrared spectral regions. The emission, excitation, and absorption spectra, as well as kinetic parameters, were measured over a broad temperature range. The Judd–Ofelt analysis was used to calculate transition rates, branching ratios, and luminescence quantum efficiencies of rare-earth doped crystals. Good agreement between theoretical and experimental results was obtained.

Evanescent wave spectroscopy for the determination of the optical constants of thin silver films deposited on a silver-halide fiber.

Abstract: An unclad silver-halide fiber was coated with a 0.1-microm silver layer and immersed in ethyl alcohol, and the fiber transmission in the range 2-20 microm was measured. The loss, induced by the metallic layer, was used to calculate the extinction coefficient, kappa', and the index of refraction, n', of the layer by fitting the experimental data with the time-independent perturbation theory in the complex region. The dependence of the extinction coefficient on the wavelength was found to be logarithmic, kappa'(lambda) = kappa(0)' exp(a lambda), and not linear, as predicted by others. This simple technique may be used to study the optical constants of thin metallic films.

Absorption spectrum of silver bromide crystals and fibers in the 9–11 μm wavelength range

Abstract: The absorption spectrum in the 9–11 μm range of both undeformed and plastically deformed AgBr crystals and polycrystalline optical fibers was investigated by tunable laser calorimetry. The observed spectral features are discussed in terms of the crystal defect structure.

Connectors, splices, and couplers for infrared transmitting optical fibers.

Abstract: Connectors, splices, and couplers are widely used in silica optical fiber systems. Until now they have not been developed for mid-infrared fibers, in spite of the recognized need for such elements in many applications such as spectroscopy, radiometry, and heterodyne detection. We describe the construction and the optical and mechanical properties of such optical components for infrared transmitting silver halide optical fibers.

Optical characterization of Nd (3+):AgBr.

Abstract: The luminescence of silver bromide crystals, doped with neodymium, was investigated over the visible and near-infrared spectral ranges The emission, excitation, and absorption spectra were measured over a broad temperature range The absolute luminescence quantum yield was estimated by comparing the luminescence with that of a neodymium-doped phosphate glass, for which the manufacturer gives a value of 04 The Judd–Ofelt analysis was applied to both materials, and transition rates, branching ratios, and quantum efficiencies were calculated for all the observed bands Good agreement was obtained between theory and experiment

Propagation of infrared radiation in silver halide optical fibers

Abstract: The relation between microscopic scattering and absorption properties, and the measurable macroscopic transmission properties of silver halide infrared fibers were investigated. Four mechanisms were considered, both by numerical simulation and far-field measurements: core scattering, surface scattering, absorption, and surface losses. The dominant mechanism in changing the angular distribution of the transmitted light was found to be the core scattering. Microscopic scattering and absorption properties were derived by fitting the experimental results.

Proceedings of Laser and Noncoherent Ocular Effects: Epidemiology, Prevention, and Treatment, Held in San Jose, California, on 10-11 February 1997.

Abstract: : The spread of laser instruments to many fields of human activity and the potential of laser radiation to produce biological damage make certain that laser accidents leading to human injuries will occur. Laser radiation is especially liable to cause accidents since it may be projected over long distances, is often used in the open space, and is sometimes invisible. The potential of laser instruments to be harmful was realized quite early on in their development, and stringent rules were imposed in most countries to minimize injuries. Those regulations are obviously effective since laser injuries are as yet uncommon and the reported cases number only in the hundreds. However, more accidental laser-inflicted traumata are expected in the future as more people are potentially exposed. The situation it especially grave in the military where lasers constitute parts of weapon systems to be used outdoors and are necessarily directed at other people. The hazards are even greater when the potential victims are using collecting optics. The facts regarding laser injuries are well known enough for some military planners to develop laser weapons aimed at producing visual incapacitation of the enemy. Some of these systems have been fielded and used. These potential weapons are based Os the fact that the eye is the body organ most vulnerable to laser radiation, especially in the visible and near-infrared wavelengths. This vulnerability is a result of the eye's dioptrics apparatus focusing the light on the retina, thus increasing the energy concentration many thousandfold. Consequently, almost all of the laser accidents reported thus far involved ocular, mainly retinal, damage.

Cavitation effects in opaque liquids produced by pulsed CO2 laser

Abstract: The formation of a stationary cavity by a sequence of CO 2 laser pulses was investigated in liquids of different viscosity and surface tension. Decreasing the surface tension of the liquid and increasing its viscosity increases the depth of the cavity and decreases the threshold energy needed for its formation. A theoretical model based on the Bernoulli-Stokes equation was developed. Good agreement between experimental and theoretical results was obtained. A method of reducing thermal damage, involving liquid layer effects during laser cutting of different materials, is proposed.