Abraham Katzir

Theory of fiber-optic, evanescent-wave spectroscopy and sensors

A general theory for fiber-optic, evanescent-wave spectroscopy and sensors is presented for straight, uncladded, step-index, multimode fibers. A three-dimensional model is formulated within the framework of geometric optics. The model includes various launching conditions, input and output end-face Fresnel transmission losses, multiple Fresnel reflections, bulk absorption, and evanescent-wave absorption. An evanescent-wave sensor response is analyzed as a function of externally controlled parameters such as coupling angle, f number, fiber length, and diameter. Conclusions are drawn for several experimental apparatuses.

The effect of complex coupling coefficients on distributed feedback lasers

The effect of complex coupling coefficients on the performance of distributed feedback (DFB) lasers is studied. The physical origins of a complex coupling coefficient are specified, and its relation with gain or loss mechanisms which occur inside the laser is discussed. Numerical results are presented for the oscillation frequencies, threshold gains, and intensity patterns of the longitudinal modes of the DFB laser.

Fiber optic sensor for chlorinated hydrocarbons in water based on infrared fibers and tunable diode lasers

A novel fiber optic evanescent wave spectroscopy (FEWS) system is based on a tunable diode laser (TDL) source, on a polymer‐coated AgClBr infrared transmitting fiber, and on a mercury cadmium telluride detector. This system was used for sensing low levels of chlorinated hydrocarbons in water. The detection limit was 100 μg/l (100 ppb), which is an improvement by a factor of 50 in comparison to a similar system that is based on a Fourier transform infrared spectrometer, and the measurement time was reduced by a factor of 3. The TDL‐FEWS system shows significant potential for in situ monitoring of ground water.

Evanescent wave infrared spectroscopy of liquids using silver halide optical fibers

Infrared spectroscopic measurements of liquids were performed in an attenuated total internal reflection cell, using infrared transparent silver halide fibers. As an example, we studied evanescent wave absorption in water. In particular, we analyzed absorption dependence on various physical parameters, such as the length of the absorbing medium and the geometry of the beam at the fiber entrance and exit faces. Absorption peaks were easily traced and experimental results correlated well with theoretical calculations. These studies may lead to practical uses of fiberoptic‐based evanescent wave spectroscopy.

Novel attenuated total internal reflectance spectroscopic cell using infrared fibers for aqueous solutions

Silver halide (AgCl:AgBr) fibers were used as the light conductor for total internal reflection measurements in a Fourier transform infrared (FTIR) spectrometer, to obtain spectra of aqueous solutions. The use of optical fibers in an attenuated total reflectance type cell with an FTIR spectrometer was demonstrated for the first time. Spectra of acetone in water and of glycine in water were acquired with the cell.

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 (3.4 ± 0.4) × 10−21 cm2, respectively.

Infrared fiber-optical chemical sensors with reactive surface coatings

Abstract A review is presented of the activity of our research group in the area of mid-infrared (MIR) fiber-optical chemical sensing systems based on the new generation of infrared-transparent fiber materials such as chalcogenide (AsSeTe) and silver halide (AgBrAgCl). The availability of these fiber materials extends the optical window utilizable for chemical-sensor systems significantly into the MIR range (2–20 μm). The increasing number of publications on this topic during recent years attests to the modified IR-transparent fibers as chemical IR sensors for the on-line analysis of IR-active compounds in aqueous solutions (chlorinated hydrocarbons, glucose) and in the gas phase (chlorofluorohydrocarbons) as developed in our laboratory.

Use of infrared fibers for low‐temperature radiometric measurements

Silver halide (AgClxBr1−x) infrared fibers were incorporated in a simple radiometer. Using this system we performed noncontact temperature measurements in the range 25–50 °C. Good correlation was found between the radiometric results and those obtained with a regular thermocouple. The minimum resolvable temperature difference was 0.1 °C and the spatial resolution was 0.9 mm.

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

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.

Polymer coated silver halide infrared fibers as sensing devices for chlorinated hydrocarbons in water

Fiberoptic evanescent wave spectroscopy (FEWS) based on AgClBr fibers and a Fourier transform infrared (FTIR) spectrometer was used for the first time to measure chlorinated hydrocarbons (CH) in water. A minimum detection limit lower than 10 mg/l was achieved by coating the fiber with low density polyethylene (LDPE), which shows reversible enrichment of CH. The response of the sensor to CH diffusion through the polymer layer was analyzed theoretically and the results were found to be in good agreement with the experiments.