Dynamics of a Spinor Exciton–Polariton System in Laterally Strained GaAs Microcavities under Resonant Photoexcitation

The evolution of the spatial coherence and the polarization has been studied in a freely decaying polariton condensate that is resonantly excited by linearly polarized picosecond laser pulses at the lower and upper sublevels of the lower polariton branch in a high-Q GaAs-based microcavity with a reduced lateral symmetry without excitation of the exciton reservoir. It is found that the condensate inherits the coherence of the exciting laser pulse at both sublevels in a wide range of excitation densities and retains it for several dozen picoseconds. The linear polarization of the photoexcited condensate is retained only in the condensate at the lower sublevel. The linearly polarized condensate excited at the upper sublevel loses its stability at the excitation densities higher a threshold value: it enters a regime of internal Josephson oscillations with strongly oscillating circular and diagonal linear degrees of polarization. The polariton–polariton interaction leads to the nonlinear Josephson effects at high condensate densities. All the effects are well described in terms of the spinor Gross–Pitaevskii equations. The cause of the polarization instability of the condensate is shown to be the spin anisotropy of the polariton–polariton interaction.     

Effect of the incoherent scattering of polaritons on the dynamics of stimulated polariton-polariton scattering in GaAs microcavities

It has been found that interband illumination strongly affects the dynamics of parametric polariton scattering in planar GaAs microcavities under resonant photoexcitation above the inflection point of the polariton dispersion curve: illumination with a power density of about 0.1% of the resonance value reduces the threshold density for the appearance of stimulated scattering by more than 15%. It has been shown that the effect is attributed to a change in the resonance energy of the pumped mode due to an increase in the density of long-lived exciton-like polaritons formed owing to the scattering of resonantly-excited polaritons on photoexcited free carriers.     

Synthesis of 2-benzoylethynylpyrroles by cross coupling of 2-arylpyrroles with 1-benzoyl-2-bromoacetylene over aluminum oxide

Cross coupling of 2-arylpyrrole with benzoylbromoacetylene over aluminum oxide at room temperature gave 45–94% of 2-(benzoylethynyl)-5-arylpyrroles. Intermediate 2-(2-benzoyl-1-bromoethenyl)-5-arylpyrroles were isolated in up to 19% yield. The reaction was accompanied by formation of less than 5% of adducts of the initial pyrroles with the cross-coupling products, 2-benzoyl-1,1-bis(5-arylpyrrol-2-yl)ethenes.     

Synthesis of Functionally-substituted Pyrrolothiazolidines from Pyrrole-2-carbodithioates, CH-acids, and Haloacetylenes

Functionally substituted pyrrolothiazolidines have been synthesized by the sequential treatment of pyrrole-2-carbodithioates with methylene-reactive nitriles and haloacetylenes in a KOH-DMSO system.     

Synthesis of Functionalized 2-(2-Pyrrolyl)pyrazolo[1,5-a]pyrimidines

Reactions of 5-amino-3-(2-pyrrolyl)pyrazoles with -dicarbonyl compounds (acetylacetone and ethyl acetoacetate) lead to formation of up to 90% of polysubstituted pyrazolo[1,5-a]pyrimidines.     

Generation of nonclassical light upon resonant excitation of a semiconductor microcavity

Strong correlations in the fluctuations of the intensity of emission from a semiconductor microcavity under resonant laser excitation are observed. The intensity correlation function exhibits an unusual oscillatory behavior with an unexpectedly long oscillation period and decay time. The visibility of the correlation function reaches 0.81. Long oscillation times are attributed to the Rabi frequency characterizing weak coupling between the electromagnetic field of the semiconductor microcavity mode and long-lived exciton states localized by the random potential of the quantum well. For a laser excitation power density of 400 W/cm², the power density of the radiation emitted by the microcavity is 12 W/cm², which corresponds to the total flux of nonclassical light of 1.5 × 10¹⁵ photons/s from an excited spot 50 μm in diameter. Thus, a microcavity can serve as a bright emitter of nonclassical light.     

Reactions of Pyrrole-1- and Pyrrole-2-carbodithioates with Activated Acetylenes

Pyrrole-1- and pyrrole-2-carbodithioates react with activated alkenes (KOH-DMSO, room temperature) along the nucleophilic addition mechanism regio- and stereospecifically to afford pyrrole-1-and pyrrole-2-carbodithioethenes. The adducts of pyrrole-2-carbodithioates under the reaction conditions undergo intramolecular cyclization into pyrrolothiazoles derivatives.     

4-Dimethylaminoacetophenone O-vinyloxime: Synthesis and steric structure

4-Dimethylaminoacetophenone oxime was synthesized from 4-dimethylaminoacetophenone and hydroxylamine hydrochloride. Its reaction with acetylene in the system KOH-DMSO gave previously unknown 4-dimethylaminoacetophenone O-vinyloxime as the major product. According to the experimental data and quantum-chemical calculations, 4-dimethylaminoacetophenone O-vinyloxime is formed as the only E isomer with preferential s-trans conformation of the vinyloxy group, which is characterized by essentially nonplanar structure.     

Stimulated polariton-polariton scattering and dynamic Bose-Einstein condensation of polaritons in GaAs microcavities under excitation near the exciton resonance

The dynamics of formation of the macroscopically occupied polariton mode at the bottom of the polariton band E _LP(k = 0) and its spin polarization under the quasiresonant pulse excitation of excitons (E = E _X ) with large values of quasi-momentum have been studied in planar GaAs microcavities. It has been found that the growth in the depth E _X − E _LP(k = 0) of the polariton band leads to the change in the formation mechanism for the k = 0 condensate state from the direct parametric decay of the photoexcited mode (due to the polariton-polariton interaction) to the dynamic condensation of polaritons, which results from the multiple scattering of polaritons by both phonons and polaritons. At the same time, in microcavities with E _X − E _LP(k = 0) > 3.5 meV, the direct decay of the photoexcited mode does not disappear, becoming an efficient mechanism for the filling of the states located at the k-space ring, corresponding to the energies E _LP(k) ≈ E _X − 2.6 meV.