Federal State Research and Design Institute of Rare Metal Industry “Giredmet”, Moscow, Russia

I. S. Lisitskiy, Head of the Laboratory of High-purity Halide Optic Materials, e-mail: gradan@mail.ru
V. F. Golovanov, Senior Researcher
G. V. Polyakova, Senior Researcher
M. S. Kuznetsov, Senior Researcher
K. S. Zaramenskikh, Senior Researcher

Crystals of silver halides AgCl, AgBr and KRS-13 (25 %wt. AgCl — 75 %wt. AgBr) is a unique material that combines high optical quality with satisfactory mechanical properties and high water resistance, widely used for the manufacture of optical fiber. To study the factors affecting the absorption of light in the fiber, the light scattering was studied in silver halide crystals grown by Stockbarger method from deeply pre-purified salts. Chemical, chemical-spectral analysis and X-ray studies of crystal structure were carried out. For optical investigations, the installation of light-scattering measurement at a wavelength of 0.63 mm was made, which allows quantitative determination of light scattering at an angle of 90^o by fixing the rotation diagrams. The diagrams of the rotation, which showed that the light scattering has a pronounced anisotropy, which has a maximum scattering in certain crystallographic directions, and also varies along the length of the ingot, were obtained. In particular, the direction <110> has maximum scattering in AgBr crystals. It was found that the scattering elements are block boundaries and pores. Heat treatment of the sample increases scattering intensity, although, as was established earlier, the sample becomes more microstructured. This is due to the increased mobility of the pores at high temperature, leading to their convergence, conglomeration and coalescence, which leads to an increase in the size of structural defects and enhances the effect of light scattering. It is shown that in the case of the growth of the crystal under conditions close to equilibrium, the absence of micro pores and microinclusions of impurity, as well as a much smaller contribution block boundaries leads to a sharp decrease in light scattering.

1. Golovanov V. F., Lisitskiy I. S., Polyakova G. V. Tsvetnye Metally — Non-ferrous metals. 2005. No. 4. pp. 73–77.
2. Israeli S., Katzir A. Optical losses of AgClBr crystals and fibers in the middle infrared. Optical materials. 2011. Vol. 33 (11). pp. 1825–1828.
3. Lewi T., Katzir A. Silver halide single-mode strip waveguides for the mid-infrared. Optics Letters. 2012. Vol. 37 (13). pp. 2733–2735.
4. Butvina L. N., Voytsekhovskiy V. V., Dianov E. M., Prokhorov A. M. Mekhanizm obemnogo rasseyaniya v polikristallicheskikh materialakh i svetovodakh srednego IK-diapazona (Mechanism of volume scattering in polycristal materials and optical fibers of average infra-red diapason). Moscow : Publishing House of USSR Academy of Sciences, 1987. 55 p.
5. Sparks M. G. Explanation of λ^–2 optical scattering and λ^–2 Strehl on-axis irradiance reduction. Journal of the Optical Society of America. 1983. Vol. 73 (10). pp. 1249–1254.
6. Kachi S., Namura K., Kimura M., Shiroyama K. Reduction of the scattering loss of polycrystalline fibers. Proceedings of SPIE. 1984. Vol. 484. pp. 128–132.
7. Lisitskiy I. S., Golovanov V. F., Polyakova G. V. Tsvetnye Metally — Non-ferrous metals. 2001. No. 4. pp. 73–76.