State Scientific Research and Design Institute of Rare-Metal Industry “Giredmet” JSC, Russia

I. S. Lisitskiy, Senior Researcher, e-mail: gradan@mail.ru
M. S. Kuznetsov, Senior Researcher
K. S. Zaramenskikh, Senior Researcher
V. F. Golovanov, Senior Researcher
G. V. Polyakova, Senior Researcher

This paper researches the influence of the processing in hydrostat with high pressure and increased temperature on the structural perfection degree and optical and laser characteristics of thallium halide crystals KRS-5 (TlBr — TlI) and KRS-6 (TlCl — TlBr) (the material, which is used in infrared and radiation equipment). The single crystals of thallium halides with 30 mm diameter and 70–100 mm length were grown by the Stockbarger method from the salts, which were purified by methods of oriented crystallization and vacuum distillation, up to the content of cationic impurities of 1·10^–5% (wt.) in the starting material. The following hydrostatic compression was carried out at the pressure by 1000 MPa, with the heating of sample to 250 ^oC during 1 hour. It was established that, after the compression, the improvement of crystals quality was observed by all investigated optical and laser parameters. The spectral transmittance of the short wave region from 0.4 to 0.8 μm, increased by 6–10% after the compression. During the irradiation by continuous CO₂ with a laser of 120 W power, the radial resistance threshold has been increased to 3–8 times. The laser radiation absorption tends to decrease (reduced by (2–5)·10^–3 cm^–1 on average). The maximum improvement of characteristics was achieved for the crystals, which were grown from low-quality raw materials (with the content of cationic impurities by 5·10^–5–1·10^–4% (wt.)). The X-ray structure study showed no significant changings of samples blocking, both in the surface layers, and in the volume (according to the misorientation between the groups of blocks and angular intervals of their distribution). The studies revealed that the method of the comprehensive hydrostatic compression could be used for the improvement of operational factors of the single-crystal optical elements of CO₂-lasers (windows, lenses, mirrors and prisms).

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