F. Moser

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.

Properties of silver halide core-clad fibers and the use of fiber bundle for thermal imaging

Abstract Optical infrared (IR) fibers with core-clad structure are of great importance because they have better qualities than unclad fibers for most IR fiber applications, especially in CO2 laser power delivery and radiometry. We have fabricated core-clad polycrystalline silver halide optical fibers with different compositions and core diameters, and although their loss is still higher than that of unclad fibers, they already have many advantages and new capabilities. The behavior of the scattering loss along these fibers and other optical properties was measured and compared with that of unclad silver halide fibers. We show that the higher loss of clad fibers results mainly from excessive scattering. The improvement in the process of fabricating clad fibers enabled the production of new elements such as single-mode fibers (SMFs) and fiber bundles for thermal imaging.

Absorption and luminescence of silver halide optical fibers

Ag halide crystals are known to be transparent in the near and middle infrared, and optical fibers extruded from such crystals, in lengths of meters, have useful transmission at the CO2 laser wavelength of 10.6 μm. It has been observed, however, that in certain cases aging and exposure to blue and ultraviolet radiation decreases the infrared transmission. These reductions can be understood in terms of recrystallization following extrusion and of photolytic darkening of the Ag halides under certain exposure conditions. The optical absorption edge of the fibers in the visible and the luminescent emission at low temperatures were measured and were found to be similar to those observed in the starting near-single-crystal preforms. The photoinduced darkening observed in fibers is characteristic of that observed in strained crystals. The large grain-boundary content and the strain present in fibers have little influence on the visible-wavelength absorption and emission characteristics but do play a role in the darkening and infrared transmission at 10.6 μm.

Core-clad silver halide fibers for CO2 laser power transmission

Core-clad optical fibers with efficient IR power delivery are essential components in the development of laser ensoscope systems for surgical applications. The fabrication of such clad fibers of high quality is still an unsolved technical problem. We have investigated parameters of the fabrication of core-clad polyscrystalline silver halide optical fibers and found conditions that yield fibers with relatively good transmittance at 10.6 micrometers (about 3 dB/meter loss) and capable of delivering output power densities up to 3 kwatt/cm2 in CW operation. This performance is lower than what we achieved in core-only silver halide fibers, but the advantage of the protection provided by the clad and a subsequent plastic overcoat, make these core-clad fibers useful in a number of CO2 power transmission applications in laser surgery.

Microwave warming of biological tissue and its control by IR fiber thermometry

The fiber-optic radiometric thermometry of surfaces with non-uniform temperature distribution was analyzed theoretically and optimization of fibers positioning was considered. An infrared fiber-optic multi-channel radiometer was used to monitor and control the temperature of samples in a microwave (MW) heating system. Several heater control algorithms were investigated and the optimal control mode was obtained. Preliminary results of biological tissue warming by microwave heating were obtained. This novel control system is reliable and precise. Such a system should be very useful for medical and industrial applications.

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.

Properties of silver halide core-clad fibers and the use of fiber bundles for thermal imaging

Optical IR fibers with core-clad structure are of great importance, because they have better qualities than unclad fibers for most IR fiber applications, especially in CO2 laser power delivery and radiometry. We have fabricated core-clad polycrystalline silver halide optical fibers with different compositions and core diameters. These fibers are easier to handle than unclad fibers and, in spite of their higher attenuation, they can transmit more power density than unclad fibers. The behavior of the scattering losses along these fibers and other optical properties were measured and compared with unclad silver halide fibers. We show that the higher losses in clad fibers result from excessive scattering. The improvement in the fabrication process of clad fibers enabled the production of new elements such as single-mode fibers and fiber bundles for thermal imaging.