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Quantum-cascade lasers (QCLs) based on InGaAs/AlInAs/InP with reflective and antireflective coatings are fabricated and studied. The manufactured lasers emit in the spectral range from 4 to 5 μm. The effect of variation in the front mirror reflectance on the output power of a QCL with a highly reflective rear mirror is investigated. It is shown that the use of an antireflective coating on the front face leads to a simultaneous increase in both the threshold current of the QCL and the slope of the light–current characteristic. This allows a higher output power to be achieved at high pump currents. In contrast, the use of a partially reflective coating on the front face not only reduces the threshold current of the QCL, but also decreases the slope of the light–current characteristic. Such QCLs may have an advantage over other emitters at low pump currents.

We report the results of a comparison of metal–dielectric mirror coatings for mid-IR quantum-cascade lasers (QCLs). Samples of QCLs with Al 2 O 3 /Ti/Au and SiO 2 /Ti/Au optical coatings are fabricated and their characteristics are studied. It is shown that the use of metal–dielectric mirror coatings allows the output optical power of devices to be increased up to 93% and their threshold currents to be reduced by 1.25 times.

Dielectric mirrors for mid-IR quantum cascade lasers are calculated. Optimal dielectric materials are selected to minimize the absorption of laser radiation. Samples of quantum cascade lasers emitting in the spectral range of 4–5 μm and having various dielectric highly reflective mirror coatings are manufactured and their characteristics are studied. It is shown that the deposition of a highly reflective Si–Si 3 N 4 coating on the back face of the laser cavity leads to an increase in the output optical power of the lasers by 71% compared to control samples without coatings. The use of a Si–SiO 2 coating makes it possible to increase the output power of the lasers by 88%.

— A hardware and software complex for estimating the dispersion distortion bandwidth and fading coherence bandwidth in a satellite (transionospheric) radio channel based on the results of GPS-monitoring of the ionosphere are theoretical substantiated and developed. The basis for solving this problem is development of a structural–physical model of the radio channel, which makes it possible to simultaneously take into account the phase dispersion of the wave and diffraction on small-scale inhomogeneities of the ionosphere. Analytical dependences of the dispersion distortion bandwidth and coherence of frequency-selective fading on the mean value and small-scale fluctuations of the total electron content of the ionosphere are obtained. It is shown that under conditions of ionospheric disturbances, the fading coherence bandwidth can be much smaller than the dispersion band. In accordance with the obtained dependences, a structure is developed for building a hardware and software complex for estimating the dispersion and coherence bandwidths of a satellite radio channel based on improvement of the method for GPS monitoring of the total electron content of the ionosphere with small-scale inhomogeneities.

The presented work considers the analysis of methods and means for assessing the technical condition of charge air coolers in vehicles in operation. Metallographic studies of the fragments of samples, identified local sections of the heat exchanger, have been carried out. Various defects of the internal heat transfer surface, caused by the influence of operational factors, have been revealed. The article also touches upon the problem of imperfection of methods and means of instrumental control of the operating parameters of the heat exchange equipment of road transport. It is proposed to carry out diagnostics of the technical condition of heat exchangers at specialized stands equipped with an instrumentation and apparatus complex. The prospects of new developments in the field of diagnostic equipment for determining the operating characteristics of heat exchangers with the ability to measure the most important parameter - heat transfer are noted. An important addition, confirming the relevance of the chosen direction of research, is the substantiation of the value of the described developments not only as a tool for measuring the parameters of the state of heat exchangers, but also to solve the problem of predicting their residual resource. The results of the conducted research are presented. Using the method of physical modeling, an algorithm has been developed for diagnosing the technical condition of the charge air cooler in operation. Issues of provision with methods and means of diagnosing parameters of heat exchangers of vehicles in operation and repair are considered.

Objective. To study the efficacy and safety of pregabalin (Lyrica) in the complex therapy of opioid withdrawal syndrome (OWS). Materials and methods. The study design was a randomized, symptom-controlled, simple, blind study with active controls. A total of 34 patients with OWS were randomized to two groups. Patients of group 1 (19 subjects) received pregabalin at a dose of up to 600 mg/day as the main substance for treating OWS, in combination with symptomatic treatment (basal and symptom-triggered). Patients of group 2 (15 subjects) received clonidine (Clofelin, up to 600 mg/day) as the main treatment agent, in combination with basal and symptom-triggered treatment. The severity of OWS, cravings for opiates, sleep disorders, anxiety, depression, and side effects were assessed daily using international validated quantified assessment scales. Results. In group 1, 15 patients (79%) completed OWS treatment, compared with seven (47%) in group 2 (p = 0.05, Fisher’s exact test). There were no statistically significant differences between groups in terms of the dynamics of the severity of OWS (perhaps because of the limited number of patients). In the pregabalin-treated group, measures of the intensity of opiate cravings decreased during treatment as compared with group 2 (p = 0.05), and similar changes were seen in relation to anxiety (p = 0.05) and depression (p < 0.05); self-assessments of wellbeing increased (p < 0.05). There were no significant between-group differences in the overall incidence of side effects, though treatment tolerance was better in group 1. Conclusions. The treatment scheme including pregabalin was effective and safe and was well tolerated by patients, providing more successful completion of detoxification programs.

The results of studies of ring quantum-cascade lasers with surface emission due to a second-order grating formed in the top cladding layers are presented. Surface emission near 7.85 μm with a low threshold current density (3.8 kA/cm 2 ), in comparison with ridge quantum-cascade lasers of the same cavity length is demonstrated. The results of measurements of the intensity distribution of the near and far fields at different pumping levels are presented. The estimated value of the angle of beam extraction relative to the surface normal is in the range 5.7°–6.7°.

The results of studies of 7.5–8.0 μm range surface-emitting ring quantum-cascade lasers are presented. A second- order diffraction grating with a calculated coupling coefficient of ~9 cm –1 is formed on the entire surface of the ring cavity by focused ion beam milling. Surface-emitting lasing at room temperature near 7.75 μm with a threshold current density of ~8 kA/cm 2 and an outer radius of the ring cavity of 202 μm is demonstrated. The results of studying the intensity distribution in the far-field near the normal to the surface showed the presence of two maxima. It is shown that the implemented coupling coefficient is not sufficient to ensure single-mode lasing in the studied ring quantum-cascade lasers.

The paper considers the dynamic and thermal interference effects on two neighbouring building models in the form of square prisms arranged at a short distance from each other. It is shown how relative positions of the models affect the specific phenomena caused by the airflow interactions.

The possibility of fabrication of 4.6 μm spectral range quantum-cascade laser heterostructures by molecular-beam epitaxy technique with non-selective overgrowth by the metalorganic vapour-phase epitaxy is shown. The active region of the laser was formed on the basis of a heteropair of In 0.67 Ga 0.33 As/In 0.36 Al 0.64 As solid alloys. The waveguide claddings are formed by indium phosphide. The results of surface defects inspection and X-ray diffraction analysis of quantum-cascade laser heterostructures allow to conclude that the structural quality of the heterostructures is high and the estimated value of the root mean square surface roughness does not exceed 0.7 nm. Lasers with four cleaved facets exhibit lasing at room temperature with a relatively low threshold current density of the order of 1 kA/cm 2 .