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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 possibility of using the thermal imaging method to assess the level of blood flow in the course of building thermograms of the surface of the hands of healthy volunteers before and after the load on the muscles was studied in this paper. The results obtained using the thermal imaging method provide objective information about the degree of blood supply to the tissues, which opens up new perspectives for evaluating skin blood flow in the dynamics. The technique is absolutely safe, non-invasive, versatile and easy to perform.

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

The stability of the g-Si 3 N 3 and g-Si 3 N 4 layers, as well as the stability of these layers on the silicon (111) surface, are discusses in this paper. The density functional theory calculations with the hybrid functionals B3LYP with Hay- Wadt effective core potentials for all the heavy atoms in a combination with Hay- Wadt valence basis were used. This article presents the results of geometric optimization for graphene-like layers of silicon nitride.

At present there are a number of reports on the development and creation of range-gate vision systems operating in the near-IR range. As radiation sources such systems usually use laser diodes or matrixes and as receiving elements are gated imaginer tubes or highly sensitive CCD matrixes. The principle of operation of such systems is quite simple. The object of observation is illuminated by short laser pulses in the infrared spectral range. In this case, the object is observed in an optical device equipped with a fast shutter opening in time with the sending of light pulses for a certain short time. In the case when the time delay between the moment of a radiation pulse and the moment of opening of the shutter is equal to the time necessary for light to travel the distance to the object and back, the observer will see only the object and the area of the space directly surrounding it. The depth of this space is determined both by the time of the open state of the shutter, and by the duration of the light pulse. This method is sometimes called the range gating method. The method makes it possible to obtain much more contrast images in comparison with conventional laser-illuminated observation systems, especially for the case of a scattering medium (fog, rain, snow, etc.). When the image is formed, the light backscatter from the previous layer of the atmosphere is eliminated by gating the photodetector system. However such systems have common fundamental drawbacks. First, laser sources of the near-IR range have a relatively low output power (in the best systems, diode matrixes arrays of the kilowatt range are used). Secondly, near-IR radiation is substantially scattered on such small inhomogeneous particles present in the atmosphere as droplets of condensate, dust particles, raindrops and snowflakes. This imposes serious limitations on the maximum visibility length in conditions of limited transparency of the atmosphere due to the exponential nature of the dependence of the absorption and scattering processes on the path length. In the literature, even the factor of maximum visibility improvement is used. This factor does not exceed 5 times. These shortcomings will be deprived of range-gate vision system based on a CO 2 laser, for which the radiation peak power of several megawatts is a successfully solved problem. Recently, there have been reports of the beginning of a wide production of photodetector arrays for the mid-IR range, for which pulse gating can be easily organized. In addition, if we use CO 2 lasers tuned on oscillation lines to create vision systems in the mid-IR range, it is not only easy to avoid difficulties associated with the selective absorption of light by the gas components of the atmosphere and water vapor, but also to create systems protected from artificial interference. Such systems will be able to quickly and easily settle from one spectral range to another when trying to jam. For example, a CO 2 laser tunable in the range of 9.2-10.8 μm can provide efficient operation on several dozen generation lines suitable for use in the absence of interaction with absorbing gas components of the atmosphere. Involving the so-called non-traditional transitions of the CO 2 molecule can increase the number of such lines to several hundred.

The feasibility of using light-emitting devices, the radiation spectrum of which has maxima at wavelengths of 1.7, 1.9, and 2.2 μm for determining the water concentration in oil and oil products (gasoline, kerosene, diesel fuel) has been demonstrated. It has been found that the measurement error can be lowered if (i) the temperature of the light-emitting diode is maintained accurate to 0.5–1.0°C, (ii) by using a cell through which a permanently stirred analyte is pumped, and (iii) by selecting the repetition rate of radiation pulses from the light-emitting diodes according to the averaging time. A meter of water content in oil and oil products has been developed that is built around IR light-emitting device–photodiode optrons. This device provides water content on-line monitoring accurate to 1.5%.

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.

The influence of defects (gallium, nitrogen and aluminum vacancies and corresponding interstitial atoms) on AlN/GaN heterointerface characteristics is discussed. The results of calculation are compared with experimental data obtained using EXAFS spectroscopy.

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 power and output beam spatial properties of the transversally diode-pumped Q-switched Nd:YAG laser with the active element surrounded by the low-absorption light-scattering layer have been investigated. The layer consisted of the bonding agent in which the solid particles, like aluminum oxide or magnesium oxide, effectively scattering the light was uniformly distributed. The particle diameter was mainly in the range of 2 – 5 μ m . It has been shown that application of such layer to the diode-pumped Q-switched Nd:YAG laser head allows suppressing the amplified spontaneous emission and/or internally circulating parasitic lasing modes. At the optimized concentration of the light-scattering solid particles the output lasing pulses with the energy of 188–210 mJ (the wavelength of 1064 nm, the pulse repetition rate of 30 Hz) and improved spatial characteristics were obtained using the pump unit based on three laser diode matrixes.

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 optimal value of the output mirror reflection coefficient providing the maximum output power under a constant level of electrical power consumption and the maximum external (slope) lasing efficiency for powerful InGaAs/AlGaAs laser diode arrays (LDA) has been estimated experimentally and theoretically. The LDA active layer overheating and amplified spontaneous emission have been taken into account. For advanced LDAs with the thermal resistance of 0.2 K/W and the internal optical loss of 0.5 cm −1 the optimal output mirror reflection coefficient is equal to 20%. This value is shifted to the high output mirror reflection coefficient side with a decrease of the LDA excitation level, the LDA thermal resistivity and the internal optical loss. It has been shown that the right selection of the output mirror reflection coefficient optimal value provides the LDA operation with 20% excess of the lasing output power and 10% excess of the external lasing efficiency.

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 present paper is aimed to development of the powerful illumination module based on powerful AlGaAs/GaAs laser diode matrix with short laser pulses, high repetition rate, given radiation divergence characteristics and stabilized parameters. Developed modification of the powerful illumination module gives the chance to realize powerful pulse laser radiation on the wavelength of 846 nm with the effective form of the laser pulse, wide range of duration from tens to hundreds of nanoseconds and the frequency of repetition rate of pulses up to 10 kHz in the set space angle of radiation 27° × 8°.

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.

A model taking into account the up-conversion processes involving the upper laser level and the presence of the unpumped regions within the active element along with the lasing transitions has been developed for the passive Q-switched ytterbium–erbium glass laser which was transversally pumped by the laser diode arrays. The results of the simulation allow determining the working point providing the stable and long-term operation of the laser. The correctness of the proposed optimized model was experimentally proved by means of a comparative investigation of the utmost permissible output lasing characteristics. The maximum output lasing pulse energy up to 16.5 mJ with the pulse duration of 11.5–16.0 ns at the wavelength of 1.535 μm has been achieved with the rectangular active element for the length of 32 mm.

A relationship between the laser diode array (LDA) near field fill factor, the power of the amplified spontaneous emission fluxes developed within the LDA active layer and the operation efficiency of the ytterbium–erbium glass laser transversally pumped by the laser diode arrays has been studied taking into account the electric and optical processes in the LDA heterostructure layers. It has been found that there is a critical value of the fill factor (0.65–0.85) below of which an abrupt rise of the ytterbium–erbium laser threshold as well as the decrease of the laser operation efficiency is observed. It has been shown that the increase in the InGaAs/AlGaAs LDA fill factor leads to the increase in the LDA threshold current related with the increase of the ASE flux power. For a suppression of the ASE flux power value it has been proposed to etch the LDA heterostructure emitter layer between the stripe contacts.

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.

The influence of amplified spontaneous emission (ASE) on the dynamic characteristics of transversely diode pumped erbium-ytterbium glass laser with Co:spinel Q-switch has been investigated. ASE cavity loss coefficient for passively Q-switched laser has been determined. The dependences of ASE cavity loss coefficient on the active element length, output mirror reflection coefficient, and initial transmission of the passive Q-switch have been defined. Laser dynamics has been modelled on the basis of the rate equation set for ion population densities and photon numbers, taking into account the amplified spontaneous emission. It has been shown that ASE accounting does not influence significantly the energy and duration of the output laser pulse. Variations of the laser turn-on time and pulse repetition rate of about 5‐10% have been revealed in the case of ASE taken into consideration.

It has been theoretically ascertained that for defect-free InGaAs and InGaN compounds the uniform distribution of indium atoms is more energetically preferable than the clustering distribution. The presence of gallium and arsenic vacancy in InGaAs and nitrogen vacancy in InGaN facilitates indium atom clustering distribution. It has been shown that the increase in the indium content in InGaAs and InGaN compounds leads to the decrease of the formation energy of gallium, arsenic and nitrogen vacancies.

The work is devoted to the development and creation of the powerful all solid–state air–cooled multiwave Nd:YAG laser integrated with the output telescope system and to the development of the LD-pumped solid–state source with the extremely narrow lasing linewidth. The laser sources are meant for operation with the multiwave aerosol LIDAR (atmosphere probing altitude is up to 40 km). Keywords—LD-pumped Nd:YAG laser; LIDAR; multiwave laser source

Physical and fabrication peculiarities which provide the high output energy and beam quality for the diode pumped erbium glass and Nd:YAG lasers are considered. Developed design approach allow to make passively Q-switched erbium glass eye-safe portable laser sources with output energy 8 − 12 mJ (output pulse duration is less than 25 ns, pulse repetition rate up to 5 Hz) and beam quality M 2 less than 1.3. To reach these values the erbium laser pump unit parameters were optimized also. Namely, for the powerful laser diode arrays the optimal near-field fill-factor, output mirror reflectivity and heterostructure properties were determined. Construction of advanced diode and solid–state lasers as well as the optical properties of the active element and the pump unit make possible the lasing within a rather wide temperature interval (e.g. from minus forty till plus sixty Celsius degree) without application of water–based chillers. The transversally pumped Nd:YAG laser output beam uniformity was investigated depending on the active element (AE) pump conditions. In particular, to enhance the pump uniformity within AE volume, a special layer which practically doesn’t absorb the pump radiation but effectively scatters the pump and lasing beams, was used. Application of such layer results in amplified spontaneous emission suppression and improvement of the laser output beam uniformity. The carried out investigations allow us to fabricate the solid-state Nd:YAG lasers (1064 nm) with the output energy up to 420 mJ at the pulse repetition rate up to 30 Hz and the output energy up to 100 mJ at the pulse repetition rate of of 100 Hz. Also the laser sources with following characteristics: 35 mJ, 30 Hz (266 nm); 60 mJ, 30 Hz (355 nm); 100 mJ, 30 Hz (532 nm) were manufactured on the base of the developed Nd:YAG quantrons.

Power, special and temporal characteristics of high–performance advanced LD–pumped solid–state laser systems emitting in the spectral ranges of 1064, 1535 and 1570 (fundamental modes) as well as 266, 355 and 532 nm (fourth, third and second harmonics) are discussed. The ways for further improvement of those laser systems are proposed. In addition, the problem of optimization of the pump unit based on the powerful laser diode arrays (LDAs) is analyzed. The effect of the LDA internal optical loss on the amplified spontaneous emission flux value developed within the LDA active layer is considered in detail.

A method of modelling the conditions for side pumping a passively Q-switched erbium laser with linear laser-diode arrays is proposed that makes it possible to determine the most efficient geometry for the placement of the linear arrays relative to the active element, taking into account the characteristics of not only the diode arrays and the active element, but also of the optical cavity that is used. The results of the modelling make it possible to choose the distance between the linear arrays and the active element and the allowable shift of the linear arrays relative to each other, and this optimizes the matching of the excitation and lasing conditions. The proposed optimization method takes into account the divergence and polarization of the radiation of the diode arrays, the geometrical and optical properties of the active element, and the configuration of the lasing mode. The theoretical results of the modelling are compared with the experimental data.

An all-solid-state multiwave laser radiator (lasing wavelengths 1064, 532, and 355 nm), integrated in a single implement with a telescope, has been developed for use in aerosol lidars. The main radiator is the master laser and an amplifier based on a YAG:Nd crystal, excited by laser diode arrays using a transverse pumping layout. In the Q-switched regime, the energy of the output pulses of the YAG:Nd laser radiator reaches 400 mJ (1064 nm). With simultaneous lasing at three wavelengths, the radiator forms radiation pulses at 1064, 532, and 355 nm, with energies of 170, 150, and 80 mJ, respectively. The pulse width is 8–11 ns at a repetition rate of 10 Hz. The developed multiwave laser radiator is effective for use as a component of aerosol lidars with an atmospheric probing range of up to 40 km.