Alla German

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.

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

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.

Spectroscopic studies of Pr 3+ ions in silver halide crystals

The luminescence of AgBr and AgBrCl crystals doped with Pr(3+) rare-earth ions was investigated in the visible and infrared spectral ranges. We measured the excitation, emission, and absorption spectra as well as the kinetic parameters over a broad temperature range. The strong influence of the silver halide composition on Pr(3+) ions spectroscopic properties was revealed. We calculated useful optical parameters for Pr:AgBr crystals by using the Judd-Ofelt approximation. Good agreement between the theoretical and the measured parameters was obtained.

Chemical sensing using infrared flattened fiber evanescent wave spectroscopy

The present paper describes a technique for enhancing the signal of fiber-optic evanescent wave spectroscopy (FEWS) in the infrared region, by flattening the sensing part of the fiber. FEWS is a novel method for measuring the absorption spectra of chemicals in contact with a segment of an optical fiber. It enables remote in-situ measurements using an optically closed system. The feasibility of FEWS for detecting chemical substances in air, water or biological liquids was proven. Theoretical computations and simulations found that the absorption signal is inversely proportional to the thickness of the fiber. These results were experimentally verified. A technique for flattening a central part of silver- halide (AgClxBr1-x) fibers was developed. Fibers of thickness down to 50 (mu) were produced, and tests proved their enhanced evanescent wave spectroscopy performance. This will be important, in particular, for water or soil pollution monitoring, where extremely small quantities of pollutants have to be detected in a solution.

Optical properties of silver-halide core/clad IR fibers

Optical fibers with low transmission losses are very useful in medical endoscopic laser surgery. In the past we developed unclad silver halide IR fibers for the transmission of carbon dioxide laser energy. We have recently developed core/clad polycrystalline silver halide optical fibers with a loss of roughly 0.3 dB/m at 10.6 micrometers. Such fibers, with a core diameter 0.35 - 0.6 mm and length of 1 to 2 meters are capable of continuously delivering output power densities as high as 14 KW/cm2. We have studied the transmission properties of these fibers for different launching conditions such as the acceptance angle at the input end and the near and far field distributions at the output end. We have also investigated the effects of bending on the optical transmission. We show that by properly designing the core/clad structure we obtain significant improvements with respect to unclad IR fibers.

LUMINESCENCE METHOD FOR THE STUDY OF ND3+ IONS DIFFUSION IN AGBR CRYSTALS

This study of diffusion of Nd in AgBr is motivated by our interest in the preparation of Nd-doped AgBr crystals that show lasing effects in the near and midinfrared. The doping can be done in several ways. We propose that monitoring the infrared luminescence along the direction of diffusion of activator ions in crystals of AgBr is a sensitive and minimally invasive method of determining the diffusion coefficient, the diffusion enthalpy, and the temperature dependence of these parameters for ions of interest. We have used this technique to study the diffusion of Nd3+ in AgBr crystals. To establish the concentration range in which the luminescence method is useful, the dependence of the luminescence kinetics on the Nd-ion concentration was investigated. The temperature dependence of the diffusion coefficient (D0=1.2×10−5 cm2/s at room temperature), and the diffusion enthalpy (H=0.51 eV) were determined. We found that high values of the diffusion coefficient and low values of the diffusion enthalpy facilitat...

High-cycle fatigue of silver halide infrared fibers

The transmission of CO(2) laser radiation by silver halide infrared fibers was measured during cyclic bending of the fibers. High-cycle fatigue of the fibers was investigated. The fibers were found to transmit without significant deterioration after more than 10(7) cycles. The fatigue-stress limit, based on 10(7) bending cycles, was estimated to be approximately 75 MPa.

Silver halide lasers and amplifiers: Nd ion diffusion in AgBr crystals

The luminescence of silver bromide crystals doped with rare earth ions (Nd3+) was investigated in the visible and near IR spectral ranges. The emission, excitation, and absorption spectra, as well as the kinetic parameters, were measured over a broad temperature range. Crystal doping was produced by growing in the melt and by a diffusion method. A novel method for measuring the diffusion profile of rare earth ions in AgBr crystals, based on the luminescence distribution of the dopant, was proposed. The luminescence parameters of AgBr:Nd crystals doped by the diffusion method were compared with these for crystals doped by adding Nd3+ to the melt. The spectroscopy parameters of Pr3+ and Er3+ ions in AgBr crystals doped in the melt were also investigated. The Judd-Ofelt analysis was applied to the rare-earth doped crystals, and transition rates, branching ratios, and quantum efficiencies were calculated. Good agreement between theory and experiment was obtained.

Diffusion of Pr3+ ions in silver halide crystals

Abstract The diffusion of Pr3+ ions in AgBr and AgCl0.77Br0.23 single crystals has been investigated by a method based on measuring the luminescence intensity distribution along the diffusion direction. The diffusion constants D0 for these crystals were 3.8×10−6 and 7.95 cm 2 / s ; and the enthalpy of diffusion H values were 0.4 and 1.25 eV, respectively. A strong influence of the silver halide composition on Pr3+-ions diffusion parameters was observed. The low value of the diffusion enthalpy found for these ions is described in terms of an associated complex 3+-ion – cation vacancy motion by an exchange mechanism. The influence of the radius of the rare earth ions on the diffusion enthalpy is discussed.

Feasibility study on optical fibers for CO2 laser power transmission

Laser power transmission experiments through silver halide discs and fibers have been performed. In these experiments cw, long pulsed and short pulsed (TEA) CO2 lasers, with power levels of 20 - 40 W or pulsed laser with energies of hundreds of mJ per pulse, have been used. The mechanical and optical properties of unclad fibers made of various alloys AgClxBr1-x with 0 < x < 1 were investigated. Compounds with x approximately equals .5 proved most suitable. They have optical losses of about .2 dB/m at (lambda) equals 10.6 micrometers and good mechanical properties.