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Background. The development of highly oriented conjugates of quantum dots (QDs) and single-domain antibodies (sdAbs) as innovative fluorescence imaging nanoprobes that specifically recognize tumor biomarkers, in particular, epidermal growth factor receptor (EGFR), is a promising approach to improving immunohistochemical tumor typing.Aim. The study was aimed at developing fluorescent nanoprobes based on QDs and sdAbs that specifically recognize EGFR, as well as evaluating their functional characteristics (size and optical properties) and functional activity.Materials and methods. QDs were obtained using high-temperature organometallic synthesis and transferred into the aqueous phase by means of stepwise replacement of ligands on the QD surface. The QDs and sdAbs were conjugated in an oriented manner using a bifunctional cross-linking agent. Detailed characteristics of the resulting conjugates were analyzed by the dynamic light scattering and immunoassay methods. Functional activity was assessed on the model human epidermoid carcinoma cells line A431.Results. The QD–sdAb conjugates have been standardized in terms of control parameters determining their functional activity, in particular, hydrodynamic diameter and efficiency of binding with target tumor cells. They are characterized by high dispersity, homogeneity, and specific functional activity towards their molecular target.Conclusion. The results demonstrate the potential use of the designed QD–sdAb conjugates for EGRF detection in immunohistochemical typing of tumor.

Introduction. It is known that the agonist of TLR-3 Poly(I:C), used as an adjuvant in a number of models of antitumor vaccines, causes inhibition of melanoma B16 growth, but the immunological aspects involved in this process have not been fully studied.The aim of the study was to evaluate changes of the immunophenotype of the spleen cells of C57BL / 6 mice caused by the tumor load and / or Poly(I:C), which is necessary for better understanding of the processes occurring during Poly(I:C) inhibition of melanoma B16-F10.Materials and methods. The immunophenotype of splenocytes of C57Bl / 6 mice was studied by flow cytometry asfollowing: the group 1 was a control (intact animals), the group 2 was mice with subcutaneously transplanted melanoma B16-F10, the group 3 was mice without a tumor treated with Poly(I:C) and the group 4 – mice with subcutaneously transplanted melanoma B16-F10 treated with Poly(I:C).Results. Median values of parameters such as the CD4 / CD8 immunoregulatory index, the percentage of CD69+ CD4+ and CD8+ T cells, the number of B and NK cells for the group of mice with melanoma treated with Poly(I:C) were between the values in the control group and in the group of mice with B16-F10. when comparing the results, the number of B and NK cells, the percentage of CD69+ on CD4+ and CD8+ T cells, their median in the group of mice with melanoma treated with Poly(I:C) was closer to the control than to the values obtained in the B16-F10 group and in the group of healthy mice receiving Poly(I:C). At the same time, we found that the total number of CD3+ cells, the number of naive CD4+ and CD8+ T cells was higher in the group of mice with melanoma treated with Poly(I:C) compared to all other groups.Conclusion. The analysis revealed the changes of the immunophenotype of murine spleen cells (CD4 / CD8, the percentage of CD69+ CD4+ and CD8+ T cells, the number of B and NK cells), which were affected by the tumor load and / or the administration of Poly adjuvant (I:C). Changes in the immunophenotype of murine splenocytes were associated with the tumor load and its size. It was also found that the splenocyte immunophenotype was affected by the repeated administration of Poly(I:C) during the tumor growth.

An autonomous non-profit organization “Center for Conflict Resolution in Medicine” is an independent forensic expert organization licensed to carry out medical activities and to conduct assessments of the quality of medical care on criminal and civil cases. It is also the clinical base of the Department of Forensic Medicine of the Pirogov Russian National Research Medical University, where the resident physicians are trained. In 2018-2019, the Center for Conflict Resolution in Medicine made 105 forensic examinations of case materials and medical documents. The organization successfully combines forensic examinations and teaching resident physicians.

A lumped model of the dynamics of the controlled switching of high-Q closed-mode structures in rectangular large cavities (up to 1 × 1 mm and larger) based on AlGaAs/InGaAs/GaAs laser heterostructures is presented. The model considers the modulation of the useful power of a closed-mode structure due to controlled generation switching to an alternative closed mode. Generation-switching control between closed mode structures is implemented due to a variation in the optical loss of one structure. A variation in the optical loss occurs due to an increase in interband optical absorption due to the quantum-confined Stark effect upon the application of voltage to a laser crystal segment in the closed-mode propagation region.

This study is concerned with the specific features of how high-Q closed modes operating on the total-internal-reflection effect in large-size (up to hundreds or thousands of wavelengths) rectangular resonators based on InGaAs/GaAs/AlGaAs laser heterostructures are formed. The specific features of the spectral composition and spatial configurations of closed-mode configurations are experimentally examined. The presence of frequency combs in the spectra is demonstrated and their correspondence to the separate spatial configurations of closed modes is shown. The effect of changing the pumping level and the temperature on the mode composition of the emission is also considered.

The results of modeling the laser generation controlled switching between high-Q closed mode structures in large rectangular cavities (up to 1x1mm) based on AlGaAs/InGaAs/GaAs heterostructures are presented. The model is based on rate equations. The basic principle of lasing switching is the controlled change in the internal optical loss due to the quantum-confined Stark effect)

The temperature behavior of operating characteristics in semiconductor lasers with a quantum-confined active region is studied with a proper account for (i) non-instantaneous capture of charge carriers from the waveguide region into the active region and (ii) internal optical loss that depends on the carrier densities. Because of (i), the carrier densities are not pinned in the lasing mode, i.e., they are functions of the injection current. In view of (ii) and as a result of pump-currentdependence of the carrier densities, so becomes the internal loss coefficient. This in turn leads to the roll-over of the light-current characteristic at high currents (i.e., decreasing optical power with increasing injection current) and, under certain conditions, appearance of the second branch in it. The laser characteristics are shown to transform qualitatively with varying temperature: they are conventional, i.e., consist of one branch, at low temperatures but they have two branches, i.e., are of a binary nature, at high temperatures. The two branches merge together at the maximum operating current beyond which the lasing quenches. In contrast to the first (conventional) lasing threshold, the threshold for emerging the second branch decreases with increasing temperature. The pump-current-dependence of the carrier densities and internal loss coefficient is also fascinating: these quantities decrease with increasing current in their second branches.

The use of liposomes as drug delivery systems today is a recognized approach to improving the effectiveness of treatment. Compared with other nanosized carriers, liposomes are highly biocompatible. However, in the literature, there are a number of data on the immunogenicity of some liposomal drugs. Hypersensitivity reactions of moderate to severe severity were noted in some patients with intravenous administration of liposomes Doxil®, Ambisome®, DaunoХome®. The technology of production of liposomes is a laborious process and obtaining liposomal forms on an industrial scale is problematic for researchers and manufacturers around the world. In connection with this, studies on the scaling up of technology for obtaining liposomes and studying the specific toxicity of liposomal preparations are relevant. Objective – evaluation of the quality of prototypes of liposomal dosage form based on tetra-3-phenylthiophthalocyanine hydroxyaluminum obtained by scaled technology in comparison with samples produced in laboratory conditions, as well as studying their mutagenic and immunotoxic properties. Object of the study – tetra-3-phenylthiophthalocyanine hydroxyaluminum liposomal, lyophilizate for the preparation of injection for injection of 1,5 mg, in bottles with a capacity of 20 ml (LLF). Materials and methods. Bengem’s method, extrusion, sterilizing filtration, lyophilization, intercellular contact integrity test (for promoter activity), Ames bacterial test, cytogenetic study of chromosomal aberrations, DNA damage test (DNA comet test), Erne method; hypersensitivity reaction of delayed type, determination of mass and cellness of central and peripheral immunity organs, evaluation of phagocytic activity of peritoneal macrophages. Results. Based on the results of the research, the LLF production technology is scaled, which allows obtaining up to 400 LLF flasks per production cycle. It has been established that LLF at doses of 6 and 24 mg/kg does not cause an increase in the number of chromosomal abnormalities in mice and does not cause DNA damage, in doses of 1,1–22,0 μg/dish LLF does not show mutagenic activity in the Ames bacterial test, in the range concentrations of 0,062–3,1 μg in the test for promoter activity does not separate intercellular contacts. It is determined that in doses of 6 and 12 mg/kg, LLF does not affect humoral and cellular immunity, does not change the mass and cellularity of the central and peripheral organs of the immune system. LLF, 24 hours after administration at doses of 6 and 12 mg/kg, dose-dependently decreases the phagocytic activity of peritoneal macrophages, which is restored after 7 days. Conclusion. The technology of LLF production is scaled. In the doses studied, it was found that LLF does not have the ability to promote the process of carcinogenesis and the lack of influence on the humoral and cellular immune response.

Due to internal optical absorption loss, which varies with carrier density in the optical confinement region, the operating characteristics can be two valued in semiconductor quantum well lasers. Particularly, there can be two lasing thresholds and two branches in the light–current characteristic. While the internal differential quantum efficiency for the first (conventional) branch of the light–current characteristic is less than 1 and decreases with increasing pump current, that for the second (unconventional) branch is greater than 1 and nonmonotonous.

The light-current characteristic (LCC) of semiconductor quantum well lasers is theoretically studied. It is discussed here that, due to internal optical absorption loss, which depends on the electron and hole densities in the optical confinement layer, (i) roll-over of the LCC occurs with increasing injection current, and, (ii) depending on the parameters of laser structures, the LCC can have two branches, i.e. the optical emission at two different output powers will be possible within a certain range of injection currents.

The operating characteristics of semiconductor quantum-well lasers, calculated with consideration for an increase in the internal optical loss in the waveguide region with increasing pump current, are presented. The condition of global electroneutrality in the structure is used. This condition consists in that the total charge of electrons in the 2D active region (quantum well) and bulk waveguide region (optical confinement layer) is equal to the total charge of holes in these two regions. Good agreement between the calculated and experimentally determined light–current characteristics is obtained.

Pulse-pumped MOVPE-fabricated (metal-organic vapor-phase epitaxy) semiconductor lasers emitting in the spectral ranges 1000–1100 and 1400–1600 nm at temperatures of 110–120 K are studied. It is found that cooling the lasers for both spectral ranges to low temperature results in their light–current curves approaching linearity, and an optical power of, respectively, 110 and 20 W can be attained. The low-temperature effect is reduced for lasers emitting in the spectral range 1400–1600 nm. The processes affecting a rise in the internal optical loss in semiconductor lasers are considered. It is shown that an increase in the carrier concentration in the waveguide of a laser structure greatly depends on temperature and is determined by the noninstantaneous capture (capture rate) of carriers from the waveguide into the active region. It is demonstrated that, upon lowering the temperature to 115K, the concentration of electrons and holes in the waveguide becomes lower, which leads to a significant decrease in the internal optical loss and to an increase in the output optical power of the semiconductor laser.

Threshold characteristics of a semiconductor quantum-well (QW) laser are calculated using the global electroneutrality condition, which includes charge carriers both in the active and waveguide regions and thus presents an equality of the total charge of electrons to the total charge of holes in these two regions. It is shown that at the lasing threshold, the densities of electrons in the QW and the waveguide region are not equal to the densities of holes in these regions, i.e., the local electroneutrality condition is violated in each of the regions. Depending on the velocities of the carrier capture from the waveguide region into the QW, the electron density can be either higher or lower than the hole density (both in the QW and in the waveguide region). The charge of the carriers of each sign in the waveguide region is shown to be greater than that in the QW.

Three laser structures with a single strained InGaAs quantum well of different depths and a GaAs or Al0.1Ga0.9As waveguide region are grown by metal-organic chemical vapor deposition. Using the experimentally determined values of the threshold current density and internal differential quantum efficiency, the velocity of electron capture into the quantum well is calculated for each of these structures. It is found that the capture velocity into deep quantum wells is significantly lower than into shallow ones.

Multiplexed suspension systems of anew generation are capable to provide precise quantitative profiling of mul- tipledisease-specific markers in human body fluids. We have developed suspension microarrays based on microbeads encoded with fluorescent nanociystals, that show undeniable advantages overavailable analogues in terms of improved multiplexing capabilities, physical and optical properties, low cost and simplicity of analysisperformance. We have adapted QD-encoded suspension microarrays for the simultaneous detection of two forms of prostate-specific antigen (PSA) in human serum by means of classical flow cytometiy. In the present study, we describe in detail the designed system properties including evaluation the microarray for quantitative analysis of serum markers in comparison to standard clinical approach ELISA, as well asestimation of the most important analytical characteristics, such as analytic sensitivity (limit of detection), reproducibility, reliability and accuracy of the analysis, the linear rangesfor detectable- marker concentrations. Experimental data suggested that the developed diagnostic system quantifies two forms of PSA in blood serum samples of patients with high accuracy, precision and reliability.

High-order surface diffraction gratings acting as a distributed Bragg reflector (DBR) in mesa stripe semiconductor lasers (λ = 1030 nm) have been studied theoretically and experimentally. Higher order interfering radiation modes (IRMs), which propagate off the plane of the waveguide, have been shown to have a crucial effect on the reflection and transmission spectra of the DBR. The decrease in the reflectivity of the DBR in response to the increase in the diffraction efficiency of these modes may reach 80% and more. According to theoretical analysis results, the intensity of the higher order IRMs is determined by the geometry of the DBR groove profile. Experimental data demonstrate that the noncavity modes are responsible for parasitic light leakage losses in the laser cavity. It has been shown that, in the case of nonoptimal geometry of the grating groove profile, the overall external differential quantum efficiency of the parasitic laser emission may exceed 45%, which is more than half of the laser output power. The optimal geometry of the DBR groove profile is trapezoidal, with the smallest possible lower base. Experimental evidence has been presented that this geometry considerably reduces the power of the higher order IRMs and minimises the parasitic light leakage loss.

Threshold and power characteristics of quantum well lasers are theoretically studied in the presence of internal optical absorption loss. Due to variation of the internal loss coefficient with electron and densities in the optical confinement layer of the laser, the light-current characteristic may have two branches, each with its own threshold. The branches merge together at the maximum operating current.

Free carrier absorption in heterostructure layers of an operating laser diode has been measured. The proposed technique is based on coupling pulse probe light emission into the laser waveguide. Lasers with various heterostructure designs were measured at different current and temperature levels up to 30 kA/cm2 and 85°C. The dependencies sufficiently describe the laser characteristics and can be used for heterostructure design comparison and optimization.

International audience; Polyelectrolyte microcapsules are promising carriers of drugs and diagnostic agents for designing targeted and controlled delivery systems design. The use of quantum dots (QDs) as fluorescent labels in bioimaging is a promising approach to bioimaging tool development. The potential toxicity of QDs makes their applicability as fluorescent labels in vivo questionable. Therefore, the cytotoxicity of polyelectrolyte microcapsules encoded with semiconductor nanocrystals has been investigated.

The operating characteristics of a semiconductor quantum-well laser calculated using three models are compared. These models are (i) a model not taking into account differences between the electron and hole parameters and using the electron parameters for both types of charge carriers; (ii) a model, which does not take into account differences between the electron and hole parameters and uses the hole parameters for both types of charge carriers; and (iii) a model taking into account the asymmetry between the electron and hole parameters. It is shown that, at the same velocity of electron and hole capture into an unoccupied quantum well, the laser characteristics, obtained using the three models, differ considerably. These differences are due to a difference between the filling of the electron and hole subbands in a quantum well. The electron subband is more occupied than the hole subband. As a result, at the same velocities of electron and hole capture into an empty quantum well, the effective electron-capture velocity is lower than the effective hole-capture velocity. Specifically, it is shown that for the laser structure studied the hole-capture velocity of 5 × 105 cm/s into an empty quantum well and the corresponding electron-capture velocity of 3 × 106 cm/s into an empty quantum well describe the rapid capture of these carriers, at which the light–current characteristic of the laser remains virtually linear up to high pump-current densities. However, an electron-capture velocity of 5 × 105 cm/s and a corresponding hole-capture velocity of 8.4 × 104 cm/s describe the slow capture of these carriers, causing significant sublinearity in the light–current characteristic.

We have studied the effect of laser cavity parameters on the light–current characteristics of lasers based on the AlGaInAs/GaInAsP/InP solid solution system that emit in the spectral range 1400 – 1600 nm. It has been shown that optimisation of cavity parameters (chip length and front facet reflectivity) allows one to improve heat removal from the laser, without changing other laser characteristics. An increase in the maximum output optical power of the laser by 0.5 W has been demonstrated due to cavity design optimisation.

We report an experimental study of power characteristics of semiconductor lasers based on MOVPE-grown asymmetric separate-confinement heterostructures with a broadened waveguide as functions of cavity length, stripe contact width and mirror reflectivities. It is shown that at high current pump levels, the variation of the cavity parameters of a semiconductor laser (width, length and mirror reflectivities) influences the light – current (L – I) characteristic saturation and maximum optical power by affecting such laser characteristics, as the current density and the optical output loss. A model is elaborated and an optical power of semiconductor lasers is calculated by taking into account the dependence of the internal optical loss on pump current density and concentration distribution of charge carriers and photons along the cavity axis of the cavity. It is found that only introduction of the dependence of the internal optical loss on pump current density to the calculation model provides a good agreement between experimental and calculated L – I characteristics for all scenarios of variations in the laser cavity parameters.

The Nobeyama Radioheliograph observation results and data from the KONUS-Wind spectrometer mounted at the Wind and RHESSI satellites on several solar flares are jointly analyzed. The analysis results for data on the flare of July 18, 2002 are described. The hard X-rays were measured in the 18 keV-15 MeV range (KONUS-Wind), and spectroheliograph measurements were carried out in the radio range at frequencies of 17 and 34 GHz. Spatial distributions of the radio brightness were calculated for the flare of July 18, 2002; they show the presence of two sources at the footpoints and one source at the top of the supposed flaring loop. The energy spectra of hard X-rays, energy flux, and the total number of accelerated electrons were found from the KONUS spectrometer data. The number of accelerated X-ray emitted electrons was estimated as N ≥ 1036, and the maximum X-ray energy flux was estimated as ∼5 × 10−6 erg cm−2 s−1. The spectrum index varies in time from −4.6 to −3.6, i.e., the soft-hard-harder trend is implemented. The spectral index of the radio waves is α ≈ −0.3 at the flare start, attains the value α ≈ −0.5 at the flux maximum, and even change the sign further. The accelerated electron transport model in the flare loop plasma is suggested for interpretation of relationships between parameters of the radio emission and hard X-rays.

Semiconductor lasers based on MOVPE-grown asymmetric separate-confinement heterostructures with a broadened waveguide and emitting in the wavelength range 1.0 – 1.1 μm are studied. It is found that the intensity of spontaneous emission from the active region increases with increasing pump current above the lasing threshold and that this is caused by a growth in the concentration of charge carriers in the active region due to the modal gain enhancement needed to compensate for the growing internal optical loss at high pulsed pump currents. It is shown that the increase in the internal optical loss with increasing pulsed pump current is one of the main reasons for saturation of the light – current characteristics of high-power semiconductor lasers.

The effect of temperature delocalization in semiconductor lasers (emission wavelength λ = 1060 nm) based on symmetric and asymmetric separate-confinement heterostructures fabricated by metal-organic vapor-phase epitaxy (MOVPE) is studied. Experimental and calculated estimates show that the carrier concentration in the waveguide increases by an order of magnitude when the temperature of a semiconductor laser is raised by ∼100°C. It is found that an increase in the temperature of the active zone leads to enhancement of the temperature delocalization of both electrons and holes. It is shown that the delocalization of holes begins at higher temperatures, compared with that of electrons. It is demonstrated experimentally that the onset of temperature delocalization depends on the threshold carrier concentration in the active region of a laser at room temperature. It is found that raising the energy depth of the active region by choosing the waveguide material makes it possible to fully suppress the temperature-delocalization process up to 175°C.

Using an extended theoretical model, which includes the rate equations for both electrons and holes, we have studied the output characteristics of semiconductor quantum-well lasers. We have found non-trivial dependences of electron and hole concentrations in the waveguide region of the laser on the capture velocities of both types of carriers from the waveguide region into the quantum well. We have obtained the dependences of the internal differential quantum efficiency and optical output power of the laser on the capture velocities of electrons and holes. An increase in the capture velocities has been shown to result in suppression of parasitic recombination in the waveguide region and therefore in a substantial increase in the quantum efficiency and output power.

A method of studying the absorption coefficient in layers of semiconductor lasers is proposed. Using lasers based on MOVPE-grown separate-confinement heterostructures with a broadened waveguide, the absorption coefficient is investigated under pulsed current pumping. It is found that when the pump current flows through the laser in question, an additional internal optical absorption arises in the heterostructure layers. It is shown that an increase in the pump current density up to 20 kA cm-2 leads to an increase in absorption up to 2.5 cm-1. The feasibility of studying free-carrier absorption in the active region is demonstrated.

The process of charge carrier delocalization in high-power semiconductor lasers is examined under high current, pulse-pumped operation conditions. It is established that the carrier delocalization process is mostly determined by the injection of electrons (rather than holes) into the waveguide. Two methods of suppression of carrier delocalization are experimentally demonstrated, which are based on increasing the waveguide bandgap width and on using the waveguide containing a potential energy barrier for electrons in the p-region.

Laser diodes with a deep built-in trapezoidal large-period diffraction grating have been developed on the basis of InGaAs/GaAs/AlGaAs heterostructures. The electroluminescence and stimulated emission spectra and light-current characteristics of diffraction-grating laser diodes have been studied. A substantial narrowing of both the luminescence and stimulated emission spectra was achieved due to the spectral selectivity of the grating. The maximum output optical power was 1 W at a drive current of 4 A. At the highest power, the lasing spectrum had a FWHM of ∼2 A. A narrowing of the lasing spectrum of the diffraction-grating laser by tens of times was demonstrated, compared with that of a laser with a Fabry-Perot cavity.

The temperature dependences of the emission characteristics of semiconductor lasers based on MOVPE-grown asymmetric separate-confinement heterostructures (wavelengths λ = 1010–1070 nm) have been studied. It was found that, in the continuous-wave mode, the main mechanism of “saturation” of the light-current characteristic with increasing temperature of the active region is carrier delocalization into the waveguide layer. It was experimentally demonstrated that the thermal delocalization of carriers depends on the energy depth of the quantum well (QW) in the active region. It is shown that the minimum internal optical loss at 140°C is obtained in laser structures with the largest energy depth of the QW of the active region.

The temperature dependences of the threshold current density and threshold concentration in semiconductor lasers based on MOVPE-grown asymmetric separate-confinement heterostructures with an extended waveguide have been studied (wavelengths λ = 1050–1070). It is shown that the temperature dependence of the threshold current density in semiconductor lasers becomes markedly stronger at above-room temperatures, which is due to temperature-induced carrier delocalization into the waveguide layers of a laser heterostructure. It was found that the sharp decrease in the thermal stability of the threshold current density with increasing temperature correlates with the coincidence of the Fermi level with the conduction-band bottom of the waveguide layer in the laser heterostructure. It is experimentally demonstrated that an increase in the energy depth and number of quantum wells in the active region of a semiconductor laser improves the thermal stability of the threshold current density. It is demonstrated that the characteristic parameter T0 attains a value of 220 K in the temperature range from −20 to +70°C.

The light-current characteristic of a semiconductor laser with multiple quantum wells (QWs) is calculated, with the delayed capture of charge carriers from the waveguide region into the wells taken into account. It is shown that increasing the number of QWs is a more effective way to improve the power characteristics of a laser, compared with an increase in the velocity of carrier capture into each of the wells. For example, using two QWs as the active region leads to a substantial increase in the internal quantum efficiency of stimulated emission and to a significantly better linearity of the light-current characteristic of the laser, compared with a single-well structure. At the same time, using three or more QWs only slightly improves the power characteristics of the laser, compared with the double-well structure. Thus, a double-well structure is the optimal as regards high output power and simplicity of growth.

A deep diffraction grating with a large period (∼2 μm) within one of the cladding layers is proposed for the implementation of selective feedback in a semiconductor laser. Frequency dependences of reflectance in the 12th diffraction order for rectangular, triangular, and trapezoidal diffraction gratings are calculated. It is shown that the maximum reflectance of the waveguide mode is attained using a rectangular or trapezoidal grating ∼2 μm deep in the laser structure. Deep trapezoidal diffraction gratings with large periods are fabricated in the Al0.3Ga0.7As cladding layer of a GaAs/AlGaAs laser structure using photolithography and reactive ion etching.

The effect of noninstantaneous carrier capture by a nanoscale active region on the power characteristics of a semiconductor laser is studied. A laser structure based on a single quantum well is considered. It is shown that delayed carrier capture by the quantum well results in a decrease in the internal differential quantum efficiency and sublinearity of the light-current characteristic of the laser. The main parameter of the developed theoretical model is the velocity of carrier capture from the bulk (waveguide) region to the two-dimensional region (quantum well). The effect of the capture velocity on the dependence of the following laser characteristics on the pump current density is studied: the output optical power, internal quantum efficiency of stimulated emission, current of stimulated recombination in the quantum well, current of spontaneous recombination in the optical confinement layer, and carrier concentration in the optical confinement layer. A decrease in the carrier capture velocity results in a larger sublinearity of the light-current characteristic, which results from an increase in the injection current fraction expended to parasitic spontaneous recombination in the optical confinement layer and, hence, a decrease in the injection current fraction expended to stimulated recombination in the quantum well. A comparison of calculated and experimental light-current characteristics for a structure considered as an example shows that good agreement between them (up to a very high injection current density of 45 kA/cm2) is attained at a capture velocity of 2 × 106 cm/s. The results of this study can be used to optimize quantum well lasers for generating high optical powers.

Threshold conditions for generation of a closed mode in the crystal of the Fabry-Perot semiconductor laser with a quantum-well active region are analyzed. It is found that main parameters affecting the closed mode lasing threshold for the chosen laser heterostructure are as follows: the optical loss in the passive region, the optical confinement factor of the closed mode in the gain region, and material gain detuning. The relations defining the threshold conditions for closed mode lasing in terms of optical and geometrical characteristics of the semiconductor laser are derived. It is shown that the threshold conditions can be satisfied at a lower material gain in comparison with the Fabry-Perot cavity mode due to zero output loss for the closed mode.

Semiconductor nanocrystals (quantum dots, QDs) have a wide range of potential application in multiplexed tissue and cell imaging, and for in vivo molecular diagnostics and therapy. Therefore studying of the toxicity of QDs and their influence on various cellular processes in vitro is necessary to understand their interaction with living systems.; The paper presents the results of studies on the evaluation of CdSe/ZnS QD cytotoxicity, as well as the results of studying their interaction with freshly prepared human monocytes in vitro. Keywords: Quantum dots, semiconductor nanocrystals, cytotoxicity, in vitro models, monocytes.

Advantages of the concept of high-powered semiconductor nanoheterostructure lasers for the spectral range 1700–1800 nm, grown by MOCVD in the InGaAsP/InP solid solution system, have been experimentally demonstrated. It has been found that using an expanded waveguide enables reduction to 2 cm−1 of the internal optical loss in quantum-well asymmetric separate-confinement double InGaAsP/InP heterostructures emitting at a wavelength of 1.76 µm. The heterostructures developed have been used to create multimode lasers with a room-temperature CW output power of 2.5 W in an aperture of 100 µm. It is shown that use of highly stressed quantum-well InGaAs layers as the active region makes it possible to obtain characteristic temperatures T0 = 50–60 K.

Results of photoluminescence (PL) studies of heterostructures with strongly strained InxGa1 − xAs quantum wells (QWs) are presented. It is shown that the dependence of the PL intensity on the QW thickness has a maximum whose position depends on the composition of the InxGa1 − xAs solid solution. The PL wavelength at the maximum intensity is 1.13 µm at a QW thickness of 60 µm at a QW thickness of 50 A for x = 0.39 and 0.42, respectively.

The possibility of using the normal skin effect in dielectric waveguides for long-wavelength radiation is analyzed. A design of a waveguide integrated with a heterolaser is suggested, in which an undoped layer of GaAs is clad between heavily-doped n- and p-AlxGa1 − x As alloy layers, reflecting radiation because of the normal skin effect. It is shown that an efficient waveguide can be formed using n-AlxGa1 − x As layers with x 5 × 1018 cm−3 and p-AlxGa1 − x As layers of any composition with the hole concentration P ≥ 3 × 1019 cm−3.

Asymmetric Al0.3Ga0.7As/GaAs/InGaAs heterostructures with a broadened waveguide produced by the method of MOCVD epitaxy are studied. It is established that the precision shift of the active region to one of the cladding layers ensures the generation of the chosen mode of high order in the transverse broadened waveguide. It is experimentally established that this shift brings about an increase in internal optical losses and a decrease in the internal quantum efficiency of stimulated emission. It is shown experimentally that the shift of the active region to the n-type cladding layer governs the sublinear form of the power-current characteristic for semiconductor lasers; in the case of a shift of the active region towards the p-type cladding layer, the laser diodes demonstrated a linear dependence of optical power on the pump current in the entire range of pump currents.

Charge-carrier heating and the carrier concentration dependence on electric current in quantum-well laser heterostructures have been studied under conditions of spontaneous and stimulated emission. Intersubband absorption in tunnel-coupled quantum wells has been investigated under charge-carrier heating by a lateral electric field and under high-power optical excitation.

The charge-carrier concentration and the temperature of hot electrons and holes in quantum-well laser nanostructures in the regimes of spontaneous and stimulated emission are determined as functions of the current density j, with InGaAs/GaAs structures as an example. Under spontaneous-emission conditions, the carrier concentration in the active region of a laser structure grows as the current increases, while carrier heating is insignificant. The spontaneous-emission spectra calculated taking into account forbidden optical transitions agree well with the experimental ones. Under stimulated-emission conditions, the behavior is quite different. When the pump current density is comparatively low (several times above the threshold), the concentration of injected charge carriers levels off and does not grow as the current increases, while the carrier temperature rises considerably. When the current density exceeds the threshold value by orders of magnitude, stabilization of the charge-carrier concentration does not take place; the carrier concentration exhibits a severalfold increase and the carrier temperature rises to about 450 K at j = 80 kA/cm2. The number of the charge carriers escaping from the quantum wells into the barriers, which determines the laser efficiency, also increases under these conditions because of the carrier heating. This undesirable effect can be weakened by increasing the depth of the quantum wells.