Absorption and luminescence of silver halide optical fibers

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Abstract
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.