Optical properties of metamorphic hybrid heterostuctures for vertical-cavity surface-emitting lasers operating in the 1300-nm spectral range

The possibility of fabricating hybrid metamorphic heterostructures for vertical-cavity surfaceemitting lasers working in the 1300-nm spectral range is demonstrated. The metamorphic semiconductor part of the heterostructure with a GaAs/AlGaAs distributed Bragg reflector and an active region based on InAlGaAs/InGaAs quantum wells is grown by molecular-beam epitaxy on a GaAs (100) substrate. The top dielectric mirror with a SiO₂/Ta₂O₅ distributed Bragg reflector is formed by magnetron sputtering. The spectra of the room-temperature microphotoluminescence of these vertical-cavity surface-emitting laser heterostructures are studied under 532-nm excitation in the power range of 0–70 mW (with a focused-beam diameter of ~1 μm). The superlinear dependence of the photoluminescence intensity on the excitation power, narrowing of the photoluminescence peaks, and a change in the modal composition may be indications of lasing. The results obtained give evidence that the technology of the metamorphic growth of heterostructures on GaAs substrates can be used for the fabrication of vertical-cavity surface-emitting lasers working in the 1300- nm spectral range.     

Influence of core configuration and arm structure on solution properties of new thermosensitive star-shaped poly(2-alkyl-2-oxazolines)

New thermoresponsive star-shaped poly(2-isopropyl-2-oxazoline) (PiPrOx) and poly(2-ethyl-2-oxazoline) (PEtOx) with arm grafting to upper rim of calix[8]arene core were synthesized and studied in aqueous solutions by light scattering and turbidimetry methods. The solution behavior was compared with that for polyoxazoline stars with varying positions of arm grafting, i.e., to lower rim of calix[8]arene. The observed growth of the phase separation temperature for PiPrOx as compared to PEtOx is explained by different dehydration temperatures of ethyl- and isopropyloxazoline units. The phase separation temperatures decrease after the changeover from lower rim grafting to upper rim one due to varying configurations of calix[8]arene.     

Microdisk Injection Lasers for the 1.27-μm Spectral Range

Microdisk injection lasers on GaAs substrates, with a minimum diameter of 15 μm and an active region based on InAs/InGaAs quantum dots, are fabricated. The lasers operate in the continuous-wave mode at room temperature without external cooling. The lasing wavelength is around 1.27 μm at a minimum threshold current of 1.6 mA. The specific thermal resistance is estimated to be 5 × 10–3 °C cm²/W.     

Effect of AlGaAs-(AlGa) x O y pedestal parameters on characteristics of a microdisk laser with active region based on InAs/InGaAs quantum dots

Effect of parameters of the AlGaAs-(AlGa) _x O _y layer forming the pedestal of a microdisk laser with an active region based on InAs/InGaAs quantum dots on specific features of the emission spectrum at a temperature of 15 K under optical excitation has been studied. A decrease in the oxidation depth of the Al_0.97Ga_0.03As layer results in a decrease in the intensity of “whispering gallery mode” lines; simultaneously, the lasing threshold becomes higher and the Q factor is diminished by increased leakages into the substrate region.     

Synthesis of the first unsymmetrical macroheterocycle containing endocyclic phosphorus atoms from pyrocatechol and hydroquinone

The first unsymmetrical phosphorus(III)-containing macrocycle having hydroquinone and pyrocatechol fragments, N,N,N′,N′-tetraethyl-2,4,11,13-tetraoxa-3,12-diphosphatricyclo[12.2.2.0^5,10]octadeca-1(16),5,7,9,14,17 hexaene-3,12-diamine, was synthesized in a stepwise mode from hexaethylphosphorous triamide, hydroquinone, and pyrocatechol. The product was converted into the corresponding P,P′-dioxide and P,P′-disulfide     

Regularity of the solution and well-posedness of a mixed problem for an elliptic system with quadratic nonlinearity in gradients

A boundary value problem for an elliptic system of equations is studied that arises in the analysis of a new hydrodynamic model describing charge transport in a planar semiconductor MESFET (metal semiconductor field effect transistor). The problem has a number of features, specifically, the equations of the system involve squared components of the gradients of the unknown functions; the boundary conditions are of a mixed character, i.e., Dirichlet and Neumann conditions are set on different portions of the boundary; and the boundary of the domain is a nonsmooth curve, namely, a rectangle. Under a certain optimal condition, the C ^1,α-regularity of a weakened solution of the problem is justified and its existence is proved, while its uniqueness is shown under additional constraints. The results are used to justify the stabilization method as applied to finding approximate stationary solutions of the hydrodynamic model.     

Polarized fluorescence of jet-cooled molecular iodine

The degree of polarized fluorescence of molecular iodine ¹²⁷I₂ cooled in a supersonic jet under rotationally selective excitation in the electronic transition B ³Π_0u ⁺-X ¹Σ _g ⁺ has been measured and calculated. It was found that the interaction of the angular momentum of the molecule with the nuclear spins of iodine atoms leads to a considerable depolarizing effect. This effect is most pronounced for small rotational quantum numbers of the angular momentum that are comparable with the total nuclear spin of the iodine molecule, which is equal to 5.     

Local-in-time well-posedness of a regularized mathematical model for silicon MESFET

We prove the local-in-time well-posedness of the initial boundary value problem for a system of quasilinear equations. This system is used for finding numerical stationary solutions of the hydrodynamical model of charge transport in the silicon MESFET (metal semiconductor field effect transistor). The initial boundary value problem has the following peculiarities: the quasilinear system is not a Cauchy-Kovalevskaya-type system; the boundary is a non-smooth curve and has angular points; nonlinearity of the problem is mainly connected with squares of gradients of the unknown functions. By using a special representation for the solution of a model problem we reduce the original problem to an integro-differential system. The local-in-time existence of a weakened generalized solution of this system is then proved by the fixed-point argument.