Time filter

Source Type

Rukhlenko I.D.,Monash University | Rukhlenko I.D.,Saint Petersburg National Research University of Information Technologies | Kalavally V.,University of Selangor
Journal of Lightwave Technology | Year: 2014

The strength of Raman interaction between optical fields propagating through a silicon-nanocrystal waveguide is known to significantly differ from that in bulk silicon and silicon-on-insulator waveguides. Here we present the first theoretical study of continuous-wave Raman amplification in silicon-nanocrystal waveguides with improved mode confinement. By calculating numerically the mode-overlap factors and effective refractive indices of the pump and Stokes fields, we analyze how the maximal Stokes intensity and the optimal waveguide length depend on the cross-section parameters of the composite, density of silicon nanocrystals, and input conditions. In particular, we demonstrate that the maximal Stokes intensity peaks at certain waveguide height and volume fraction of silicon nanocrystals for fixed input intensities, and at certain waveguide width for fixed input powers. These features enable simple performance optimization of Raman amplifiers and lasers based on silicon nanocrystals. © 2013 IEEE.

Bespalov V.G.,Saint Petersburg National Research University of Information Technologies
Russian Physics Journal | Year: 2016

Principles of recording the amplitudes and phases of wave fields in the terahertz (THz) frequency range are considered and methodology and schemes used for imaging in this range are analyzed. Generation of THz radiation by femtosecond optical pulses and registration of THz electric field waveforms allow the methods for holographic recording and image restoration to be developed. Results of the experiments on reconstruction of phase characteristics of THz field by the suggested holographic method are demonstrated and the influence of the experimental parameters on the quality of image restoration in time-resolved THz holography is analyzed. © 2016 Springer Science+Business Media New York

Govorov A.O.,Ohio University | Zhang H.,Ohio University | Demir H.V.,Bilkent University | Demir H.V.,Nanyang Technological University | And 2 more authors.
Nano Today | Year: 2014

The paper reviews physical concepts related to the collective dynamics of plasmon excitations in metal nanocrystals with a focus on the photogeneration of energetic carriers. Using quantum linear response theory, we analyze the wave function of a plasmon in nanostructures of different sizes. Energetic carriers are efficiently generated in small nanocrystals due to the non-conservation of momentum of electrons in a confined nanoscale system. On the other hand, large nanocrystals and nanostructures, when driven by light, produce a relatively small number of carriers with large excitation energies. Another important factor is the polarization of the exciting light. Most efficient generation and injection of high-energy carriers can be realized when the optically induced electric current is along the smallest dimension of a nanostructure and also normal to its walls and, for efficient injection, the current should be normal to the collecting barrier. Other important properties and limitations: (1) intra-band transitions are preferable for generation of energetic electrons and dominate the absorption for relatively long wavelengths (approximately >600 nm), (2) inter-band transitions efficiently generate energetic holes and (3) the carrier-generation and absorption spectra can be significantly different. The described physical properties of metal nanocrystals are essential for a variety of potential applications utilizing hot plasmonic electrons including optoelectronic signal processing, photodetection, photocatalysis and solar-energy harvesting. © 2014 Elsevier Ltd.

Reshchikov M.A.,Virginia Commonwealth University | Usikov A.,Nitride Crystals Inc. | Usikov A.,Saint Petersburg National Research University of Information Technologies | Helava H.,Nitride Crystals Inc. | Makarov Y.,Nitride Crystals Inc.
Applied Physics Letters | Year: 2014

Many point defects in GaN responsible for broad photoluminescence (PL) bands remain unidentified. Their presence in thick GaN layers grown by hydride vapor phase epitaxy (HVPE) detrimentally affects the material quality and may hinder the use of GaN in high-power electronic devices. One of the main PL bands in HVPE-grown GaN is the red luminescence (RL) band with a maximum at 1.8 eV. We observed the fine structure of this band with a zero-phonon line (ZPL) at 2.36 eV, which may help to identify the related defect. The shift of the ZPL with excitation intensity and the temperature-related transformation of the RL band fine structure indicate that the RL band is caused by transitions from a shallow donor (at low temperature) or from the conduction band (above 50 K) to an unknown deep acceptor having an energy level 1.130 eV above the valence band. © 2014 AIP Publishing LLC.

Malashin R.,Saint Petersburg National Research University of Information Technologies
Journal of Physics: Conference Series | Year: 2014

Matching of digital images is very challenging computer vision problem. The aim of investigation was developing of algorithms for matching real aerial and cosmic photographs. In the proposed methods, images are described locally by scale and rotation invariant descriptors. Reliability and high accuracy of the algorithms has been achieved by combining dense keypoint detector and robust descriptor with complex procedure of outlier elimination. The algorithms are capable of making correct decisions when number of local mismatches is more than 99%. © Published under licence by IOP Publishing Ltd.

Discover hidden collaborations