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Transmission spectra of a ZnSe sample diffusion-doped with Fe2+ ions have been measured in the wavelength range 500 - 7000 nm. A broad absorption band in the range 500 - 1500 nm has been observed in both doped and undoped regions of the sample. This band is possibly due to deviations from stoichiometry in the course of diffusion doping. The transmission of the Fe2+:ZnSe sample at a wavelength of 2940 nm has been measured at various dopant concentrations and high peak pulse intensities (up to 8 MW cm-2). The samples have been shown to be incompletely bleached: during a laser pulse, the transmission first increases, reaches a maximum, and then falls off. Our results suggest that the incomplete bleaching cannot be accounted for by excited-state absorption. The incomplete bleaching (as well as the transmission maximum) is due to the heating of the sample, which leads to a reduction in upper level lifetime and, accordingly, to an increase in absorption saturation intensity.

We have studied UV excitation spectra of IR luminescence in bismuth-doped glasses of various compositions and obtained energy level diagrams of IR-emitting bismuth-related active centres (BACs) associated with silicon and germanium atoms up to [?]5.2 eV over the ground level. A possible energy level diagram of the BACs in phosphosilicate glass has been proposed. The UV excitation peaks for the IR luminescence of the BACs in the glasses have been shown to considerably overlap with absorption bands of the Bi3+ ion, suggesting that Bi3+ may participate in BAC formation.

The linear and nonlinear transmission of Fe2+:ZnSe crystals is measured at a wavelength of 2940 nm in the temperature range 20 - 220 degC. It is found that, with increasing temperature from 20 degC to 150 - 220 degC, the transmission of Fe2+:ZnSe crystals decreases in the case of incident radiation with an intensity of [?]5.5 MW cm-2 and increases in the case of radiation with an intensity of 28 kW cm-2. At a temperature of 220 degC, the linear transmission almost coincides with the nonlinear transmission. The transmission spectra of Fe2+:ZnSe crystals at temperatures of 22 and 220 degC in the wavelength range 500 - 7000 nm are presented.

We present the results of interference studies of a diode-pumped active disk element made of a gadolinium -- gallium -- garnet (GGG:Nd) crystal. The disk is cut perpendicular to the crystallographic axis [001], along which the pump beam propagates. With absorbing pump radiation, a thermal lens, which has been investigated by the interference methods using linearly polarised probe radiation, is formed in the disk. At the absorbed pump power up to 12 W, the interference pattern near the disk surface is a system of concentric rings. With increasing absorbed pump power up to 24 W, the outer rings transform into hexagons. It is shown that such an interference pattern in the garnet crystal is caused by thermally induced birefringence.

Optical fibre preforms and fibres with a bismuth-doped silica core containing no other dopants have been fabricated by the powder-in-tube technique. The optical loss has been measured for the first time in such fibres in a wide spectral range, from 190 to 1700 nm. We have studied the luminescence of active bismuth centres and the luminescence lifetime for some of their bands in both the preforms and the fibres drawn out from them.

We present the results of interference studies of a diode-pumped active disk element made of a gadolinium — gallium — garnet (GGG:Nd) crystal. The disk is cut perpendicular to the crystallographic axis [001], along which the pump beam propagates. With absorbing pump radiation, a thermal lens, which has been investigated by the interference methods using linearly polarised probe radiation, is formed in the disk. At the absorbed pump power up to 12 W, the interference pattern near the disk surface is a system of concentric rings. With increasing absorbed pump power up to 24 W, the outer rings transform into hexagons. It is shown that such an interference pattern in the garnet crystal is caused by thermally induced birefringence.

Optical fibre preforms and fibres with a bismuth-doped silica core containing no other dopants have been fabricated by the powder-in-tube technique. The optical loss has been measured for the first time in such fibres in a wide spectral range, from 190 to 1700 nm. We have studied the luminescence of active bismuth centres and the luminescence lifetime for some of their bands in both the preforms and the fibres drawn out from them.

The efficient technology is developed for growing high-quality doped single-crystal fibres by the mini-pedestal method with laser heating. The technology can be used to fabricate high-quality doped single-crystal fibres with a controllable radial gradient of the refractive index. The refractive-index profile in single-crystal fibres is studied experimentally. The efficient operation of a Nd3+: YAG single-crystal fibre laser in the waveguide regime was demonstrated upon longitudinal pumping by a laser diode.

The efficient technology is developed for growing Cr- and Ca-doped gadolinium—gallium garnet single-crystal films of thickness up to 100 μm on large substrates (76 mm) by the method of liquid-phase epitaxy from a solution—melt. The dependences of the absorption spectra of films and optical losses at 1 μm on the growth conditions and the solution—melt composition are studied. It is shown that Cr4+ions are formed in the films, and these films can be used as passive Qswitches in lasers.