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The operating principle and features of the oscillating process for a three-wave CO2 laser with acousto-optic Q-switching are described. Optimization of the active-medium composition and its excitation conditions as well as the choice of oscillating lines allow oscillation with an output power up to 5 W per line in a stable multiwave mode to be obtained. An efficient Q-switching method for a three-wave CO2 laser is demonstrated and enables the output radiation to be controlled in both a wide spectral range and a wide range of modulation frequencies. A method for separating signals with different wavelengths by spacing signals in time has been experimentally implemented using an external selective modulator to simplify data acquisition and processing.

The Varshni parameters of the temperature dependence of the bandgap energy in the range 10–313 K and the temperature dependence of the spin–orbit splitting energy have been calculated using experimental data obtained for an InAs0.88Sb0.12 active layer. Amplified luminescence was observed in the range 10–35 K for LEDs based on InAs0.88Sb0.12/InAsSbP heterostructures. The sharp drop in radiation intensity of InAsSb/InAsSbP LEDs at temperatures >32 K was due to extensive growth of the CHCC Auger-recombination process while the CHSH process was the dominant Auger-recombination process at temperatures

We report theoretical and experimental study of diffusion processes at GaN/AlN interfaces. Using climbing image nudged elastic band method with density functional theory (DFT) we have calculated migration barriers for vacancy-mediated self-diffusion in group-III element sublattice in AlN and GaN, for Ga diffusion in AlN and for Al diffusion in GaN. Attempt frequencies for this diffusion processes have been estimated based on harmonic transition state theory, and Al-Ga interdiffusion coefficient has been calculated. The calculations are in agreement with experimental results for GaN/AlN superlattices obtained by extended X-ray absorption fine structure (EXAFS) spectroscopy and transmission electron microscopy.

A system of balance equations is used to calculate the time (t) dependence of the intensity (I) of the output of a Nd:YAG laser rod from the time a pump pulse is applied for different levels of excitation of the rod by arrays of laser diodes (transverse pump configuration). Comparison of the calculations with experimental data shows that an analysis of the I(t) curves can be used to determine the contributions of amplified luminescence and parasitic lasing modes, which do not leave the volume of the active medium, to the overall loss of pump radiation energy. The model approach developed here can be used to evaluate the quality of the active media in diode-pumped solid-state lasers.

The spectral characteristics of light emitting diodes based on a InAs/InAsSb/InAsSbP heterostructure, which emit in a wavelength range of 3.5–4.5 µm, are investigated experimentally. It is shown that the temperature shift of the maximum emission wavelength of a light emitting diode in the temperature range 80–313 K is 1.8 nm/K. The temperature dependence of the band gap of the InAs0.88Sb0.12 active layer is described by the Varshni formula with the characteristic parameters: Eg0 = 0.326 eV, a = 2.917 × 10–4 eV/K, and s = 168.83 K. The results of our measurements of the concentrations of carbon dioxide (CO2) using the studied light emitting diodes show the possibility of the reliable detection of CO2 in the concentration range 300–100000 ppm.

We have studied an all solid-state diode-side-pumped laser which lases in the nominally eye-safe spectral range of ~1.5–1.6 μm. The optical configuration of the laser is based on using a potassium gadolinium tungstate crystal doped with neodymium ions, in which lasing occurs at a wavelength of λ = 1.351 μm and stimulated Raman selfconversion occurs to the first Stokes component (λ = 1.538 μm). The maximum output pulse energy was 17 mJ and 7 mJ for repetition frequencies of respectively 1 Hz and 10 Hz.

The energy levels of gallium and arsenic vacancies as well as silicon impurities in the band gap of InxGa1 − x As have been found as functions of the indium content. The effect of defects on the lasing output power and on the optimal reflection coefficient of output mirrors of laser diode arrays (LDAs) based on the In0.11Ga0.89As/AlGaAs heterostructures has been estimated. It has been shown that the lasing output power of LDAs whose active level contains defects with deep energy levels in the band gap is substantially lower (with other conditions being the same) than that of LDAs with shallow level defects in their active layers.

The results of calculation of nitrogen vacancy geometry in GaN/AlN heterointerface and its comparison with experimental data are discussed in the paper. The methods of calculation of point defects geometry in the GaN/AlN interface within the frameworks of self-consistent field and density functional theory are compared.

The results of the influence of point defects (vacancy with interstitial atom) on the GaN/AlN heterointerface is presented. It was ascertained that presence of Al atom vacancy in the heterointerface leads to the contacting layer atoms rearrangement. The presence of N atom vacancy does not influence on the contacting Ga and Al layers intermixing.

The development of amplified luminescence fluxes in powerful InGaAs/AlGaAs laser diode arrays (lasing wavelength 940–960 nm) has been studied experimentally and theoretically at pump levels above the threshold value. Flux density values for amplified luminescence propagation along (1.88⋅109 W/m2) and across (1.21⋅109 W/m2) the laser diode array cavity axis have been evaluated for the threshold pump level at room temperature (293 K). The contribution of the recombination rate induced by the amplified luminescence to the threshold current generation of the laser diode array reaches 7%. It has been shown that the amplified luminescence flux density is increased by 49% as the pump level rises from one to three threshold values.

A system of radiative transfer equations is used to calculate the loss coefficient for amplified luminescence fluxes propagating along and transverse to the cavity axis in the active layer of high-power laser diode arrays taking the spreading of charge carriers in the cladding and contact layers of InGaAs/GaAs/AlGaAs heterostructures into account. It is shown that the spreading of charge carriers leads to a significant change in the amplified luminescence flux which can contribute up to 18% to the lasing threshold of these laser diode arrays. The calculated loss coefficients can greatly simplify the determination of the amplified luminescence fluxes in laser diode arrays with an error of less that 16% and can be used to determine how much the amplified luminescence affects the power and dynamic characteristics of diode arrays.

On the base of density functional theory (DFT) calculations, it was ascertained that the GaN/AlN heterointerfaces without Al and Ga contacting layers intermixing and with the total substitution of the contacting layers are energetically more probable than the heterointerfaces with another amount of intermixing. The displacement of nitrogen atom from its site to second coordinate sphere between Ga and Al contacting layers is more probable than the displacement to the Al part of the cluster. The presence of nitrogen atom vacancy in the heterointerface does not influence the Al and Ga contacting layers intermixing, but complex defect nitrogen vacancy + interstitial N atom in the second coordinate sphere can be stable in contrast to the case of Al vacancy + interstitial Al atom in the second coordinate sphere. On the base of comparison of calculated and experimental data, it was ascertained that the most probable location of nitrogen vacancy in the vicinity of GaN/AlN interface is the location in the first Ga layer in respect to the GaN/AlN interface.