Influence of the surface roughness of silver halide fibers on their transmission in the near infrared

Silver halide crystals are highly transparent from the visible to the mid-infrared, but fibers extruded from these crystals have low transmission in the near infrared in the spectral range 1-3 μm. We found that this low transmission is partly due to surface roughness and that it can be highly improved by treatment with potassium cyanide solution. Using the Rayleigh criteria for a simple planar waveguide model, we showed that the attenuation due to surface roughness is theoretically dependant on the square of the roughness and on the inverse square of wavelength. Experimentally, the measured surface attenuation indeed follows this behavior. The reduced attenuation in the near infrared is crucial, especially for applications such as the development of silver halide fiber lasers.