  Optical properties of hollow-core revolver fibers are numerically
investigated depending on various parameters: the hollow-core diameter, the
capillary wall thickness, the values of the minimum gap between the
capillaries, the number of capillaries in the cladding and the type of glass
(silica and chalcogenide). Preliminary, similar calculations are made for
simple models of hollow-core fibers. Based on the obtained results, the optimal
design of the revolver fiber for Raman laser frequency conversion (1560 nm to
4420 nm in H2) was determined. As a result, efficient ns-pulsed 4420 nm Raman
laser based on H2-filled revolver silica fiber is realized. Quantum efficiency
as high as 36 % is achieved and output average power as high as 250 mW is
demonstrated.
