N. Barkay

Mechanical properties of mixed silver-halide crystals and polycrystalline optical fibers

Mechanical properties of mixed AgClxBr1−x (0≤x≤1) crystals and extruded polycrystalline optical fibers were investigated as a function of composition. The microhardness of as‐grown crystals, annealed samples, and fiber‐end faces show solid‐solution hardening in agreement with the Kataoka–Yamada model [Jpn. J. Appl. Phys. 16, 1119 (1977)]. The fibers have a tensile strength of 50–90 MPa with similar solid‐solution strengthening. The infrared transmission of 0.9‐mm‐diam fibers is not reduced significantly upon bending them 90° on a 3‐mm radius. Such mixed‐crystal‐based silver‐halide fibers are suitable for many infrared optical applications.

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.

Research and development on silver halide fibers at Tel Aviv University

This paper presents a survey of current work at Tel Aviv University on properties and applications of silver halide infrared transmitting fibers. Various infrared spectral features of core-only fibers, extruded from pure mixed halide crystals of composition AgClBr1(O < x < 1), are presented and discussed. In the best fibers, total loss is as low as 0.15 dB per meter at a wavelength of 10.6 jim. The fibers can be repetitively bent on a 5 cm radius without degrading the transmission, up to thousands of bends. Fibers witha smooth core-clad structure have also been fabricated, but the optical losses are still relatively high. Novel applications of these fibers in spectrophotometry and radiometry are described.

Absorption edges of mixed silver‐halide crystals and polycrystalline optical fibers

Optical absorption edges of mixed AgClxBr1−x (0≤x≤1) crystals and polycrystalline fibers were investigated as a function of composition. Both visible edge, resulting from electronic transitions, and infrared edge due to multiphonon processes behave as the one‐mode (amalgamation) type of mixed crystals, shifting continuously with composition. Quantitative expressions were used to discuss the results. Polycrystalline extruded fibers preserve this spectral window of silver‐halide crystals, except for slight deviations which are explained by the small‐grain structure of the fibers.

Elasticity of mixed silver‐halide polycrystalline optical fibers

The elastic strain limit of polycrystalline mixed AgClxBr1−x fibers was studied. These fibers are useful as flexible infrared optical fibers, and the elastic bending regime is preferred for applications which require many bending cycles. The experimental method was based on the spring‐back upon releasing a stressed material, and used specifically calculated expressions. Elastic strain limit values are in the range of 0.15%–0.4%. They depend on composition going through a maximum at around the AgCl0.5Br0.5 composition. The dependence on composition is explained by a theoretical model, which is based on a solid‐solution internal stress field, and uses material constants.

Mechanical resistance of silver halide infrared fibers

Flexibility resistance of silver-halide infrared fibers was investigated in the plastic bending regime, which is especially useful for internal medical applications. The CO2 laser transmission of the fibers was measured in several positions while being bent. The fibers have been found to operate even after large plastic deformations, and values for various fibers and bending conditions are reported.

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.

Optical Properties Of Mixed Silver Halide Crystals And Polycrystalline Optical Fibers

The spectral window of mixed AgClxBr1-x (0≤x≤1) crystals and polycrystalline fibers was investigated as a function of composition. Both visible edge, resulting from electronic transitions, and infrared edge due to multiphonon processes, behave as the one-mode (amalgamation) type of mixed crystals, shifting continuously with composition. The extruded polycrystalline optical fibers preserve the spectral window of silver-halide crystals. Deviations which slightly broaden the window in the infrared regime are explained by the fibers small-grain structure.

Mechanical fatigue monitoring using absorption spectroscopy of infrared fibers

The spectral transmittance of infrared fibers was measured while they were undergoing flexing procedures leading to mechanical fatigue. Microscopic mechanical defects were detected through their influence on the optical losses, without interfering with the deformation. Such experiments were successfully carried out on infrared transmitting silver‐halide polycrystalline fibers. The spectral characterization provides a probe of the defects, as their effect is related to the ratio between defect size and wavelength. The method discussed here may be used to examine theoretical models concerning the dynamics of mechanical defects and optical guiding in fibers with defects.