A demonstration of narrow linewidth, low threshold OPO is presented. Two basic line-narrowing methods are applied. One method employs an intra-cavity grazing incident grating, and compensates the high losses caused by the grating by adding a laser gain element to the cavity. In the second method, a single element birefringent filter with low insertion loss is introduced in the cavity. Both configurations allow an efficient, compact design of tunable source with low pump threshold and narrow linewidth.
Bundles of silver halide optical fibers have been fabricated by extrusion of preforms containing core-clad fibers. Silver halide fibers are transparent in the mid-IR spectral range (2 - 20 micrometers ), and therefore ordered arrays of such fibers have the potential to deliver thermal images at room temperature. Several kinds of bundles were prepared, consisting of 100 to 2500 fibers, with a fill factor of 0.34. Thermal images were delivered through the bundles and recorded using a IR cooled camera. This paper discusses the optical properties and the imaging characteristics of bundles with several fiber densities of 3 - 160 fibers per mm2 and lengths up to 30 cm. The modulation transfer function of the bundles was measured by the knife edge sampling process, and by `bar-chart' imaging. The maximum spatial frequency that could be resolved after passing through a typical bundle was 3.5 lines per millimeter.
We describe a Fourier transform infrared-attenuated total internal reflectance (FTIR-ATR) technique for samples of 10 - 30 (mu) g deposited on a polycrystalline silver halide fiber. A protein deposit consists of approximately two molecular layers, for which the kinetics and extent of exchange with D2O/N2 are readily measured. We have extended the technique in several ways. Formation of complexes with modest association constants by taking advantage of the combination of protein mobility on the fiber with the absence of water. Association is thus favored, and the rates and extent of deuterium-hydrogen exchange may be followed as well as conformational changes. Polarized spectra of red blood cell ghosts have been measured on a flattened silver halide fiber. The cells containing the silver halide fibers have a design that allows controllable access to the sample. In addition to requiring only small quantities for good spectra, the cell is readily cleaned and handled. We anticipate the application of these techniques to many other biological samples, including mutant proteins.
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.
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.
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.