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Recently optical capillaries modified by Bragg reflection mirrors applied on the inner walls have been investigated for transmitting radiation of MIR lasers. Such capillaries include Bragg and omniguide fibers, holley fibers, or silica Kagome like fibers. Although OmniGuide fibers are commercially available and have been used for delivery of radiation of CO2 fibers at 10.6 μm, novel types of hollow-core fibers are still investigated for MIR applications. In this paper a novel approach for the preparation of capillary optical fibers for MIR region is presented. This approach employs the application of thin layers of arsenic sulfide glass and acrylate polymer from their solutions onto the inner wall of silica capillary. Arsenic sulfide forms high-index and polymers the low-index parts of reflection mirrors. By controlling optical thicknesses of such layers, Bragg mirrors can be obtained. In experiments, input solutions of arsenic sulfide in n-propylamine and UV-curable acrylate in acetone were prepared. Such solutions were applied by dip-coating method on glass slides in order to obtain samples of single layers and multilayer coatings for the determination of thicknesses and refractive indices. Acrylate layers were UV cured and arsenic sulfide layer were thermally treated at 80°C. By passing columns of the input solutions through a silica capillary with a hole diameter of 80 μm and a length of 50 cm multilayer coatings on the inner capillary wall were prepared. The column velocity for each solution was controlled as a main factor influencing the layer thickness. Applied layers were UV cured or thermally treated under a nitrogen flow through the capillary. Coatings of three pairs of the high- and low-index layers were fabricated. Single layers and multilayers applied on planar substrates were characterized by transmission spectroscopy and by optical microscopy. Attenuation coefficients of internally coated capillary fibers of 10-20 dB/m were determined at a wavelength of 1940 nm.
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