Low saturation fluence in a semiconductor saturable electroabsorber mirror operated in a self-biased regime

A semiconductor saturable absorber mirror utilizing the electroabsorption effect on a self-biased stack of extremely shallow quantum wells is proposed and analyzed theoretically and numerically. The saturation flux and recovery time of the proposed device when operated with picosecond incident pulses are shown to compare very favorably with existing all-optical constructions. (C) 2008 American Institute of Physics

Laser diode structures with a saturable absorber for high-energy picosecond optical pulse generation by combined gain-and Q-switching

The performance of gain-switched Fabry-Perot asymmetric-waveguide semiconductor lasers with a large equivalent spot size and an intracavity saturable absorber was investigated experimentally and theoretically. The laser with a short (∼20 μm) absorber emitted high-energy afterpulse-free optical pulses in a broad range of injection current pulse amplitudes; optical pulses with a peak power of about 35 W and a duration of about 80 ps at half maximum were achieved with a current pulse with an amplitude of just 8 A and a duration of 1.5 ns. Good quality pulsations were observed in a broad range of elevated temperatures. The introduction of a substantially longer absorber section leads to strong spectral broadening of the output without a significant improvement to pulse energy and peak power

Theory of direct and indirect effect of two-photon absorption on nonlinear optical losses in high power semiconductor lasers

The effect of the transverse laser structure on two-photon absorption (TPA) related effects in high-power diode lasers is analysed theoretically. The direct effect of TPA is found to depend significantly on the transverse waveguide structure, and predicted to be weaker in broad and asymmetric waveguide designs. The indirect effect of TPA, via carrier generation in the waveguide and free-carrier absorption, is analysed for the case of a symmetric laser waveguide and shown to be strongly dependent on the active layer position. With the active layer near the mode peak, the indirect effect is weaker than the direct effect due to the population of TPA-created carriers being efficiently depleted by their diffusion and capture into the active layer, whereas for the active layer position strongly shifted towards the p-cladding, the indirect effect can become the dominant power limitation at very high currents. It is shown that for optimizing a laser design for pulsed high power operation, both TPA related effects and the inhomogeneous carrier accumulation in the waveguide caused by diffusive current need to be taken into account

High-energy sub-nanosecond optical pulse generation with a semiconductor laser diode for pulsed TOF laser ranging utilizing the single photon detection approach

Bulk and quantum well laser diodes with a large equivalent spot size of da/Γa ≈ 3 µm and stripe width/cavity length of 30 µm/3 mm were realized and tested. They achieved a pulse energy and pulse length of the order of ~1 nJ and ~100 ps, respectively, with a peak pulse current of 6–8 A and a current pulse width of 1 ns. The 2D characteristics of the optical output power versus wavelength and time were also analyzed with a monochromator/streak camera set-up. The far-field characteristics were studied with respect to the time-homogeneity and energy distribution. The feasibility of a laser diode with a large equivalent spot size in single photon detection based laser ranging was demonstrated to a non-cooperative target at a distance of a few tens of meters

Solution of quasi-periodic fracture problems by the representative cell method

Abstract A general scheme for the solution of linear elastic quasi-periodic fracture problems is presented. The simplest type of such problems is characterized by a nonperiodic stress state in a domain with translational symmetry. Employing the discrete Fourier transform reduces the initial problem to a problem of a representative cell with speci®c boundary conditions which may be solved analytically or numerically. The procedure for solving the problem by the ®nite element method is developed. The suggested technique is employed for the solution of the problem of antiplane deformation of a strip weakened by a periodic array of arbitrary loaded cracks

Threshold and power of pulsed red‐emitting diode lasers with a bulk active layer near p‐cladding under high‐temperature operation

Threshold properties and pulsed output of AlGaInP visible-emitting lasers with an asymmetric waveguide structure and a bulk active layer are analysed. The efects of the current leakage, increased by the heating of the laser due to the proximity of the electrical pulse source and the Joule heating in and around this source are analysed. When optimising the laser design, waveguiding properties of the bulk active layer are shown to be important, leading to threshold currents decreasing, and injection efciency increasing, with active layer thickness in lasers with moderately thick (<0.1 μm) active layers

Polarization stabilization in vertical-cavity surface-emitting lasers through asymmetric current injection

We present experimental evidence that asymmetric current injection in intracavity contacted vertical-cavity surface-emitting lasers (VCSELs) stabilizes the polarization of the emitted light. Anisotropies in the gain and loss mechanisms introduced by asymmetric current injection are considered to explain this effect. The design scheme opens perspectives to obtain actual polarization control in VCSEL

MODIFICATION OF RYANODINE-SENSITIVE CALCIUM RELEASE CHANNELS GATING AND CALCIUM DYNAMICS IN CARDIOMYOCYTES BY TEMPERATURE IN ELECTRON-CONFORMATIONAL THEORY

We took into account a temperature in an Electron-Conformational Model of SR-based Ca2+ Clock (ECM Clock). The results of modelling of ECM Clock show that higher temperature gives lower amplitude of cytosolic Ca2+ and higher frequency of oscillations and lower temperature destroys ECM Clock.Исследования поддержаны Программой повышения конкурентоспособности ведущих университетов РФ (постановление Правительства РФ № 211 от 16 марта 2013 г.)

Transcriptomic Changes Due to Cytoplasmic TDP-43 Expression Revel Dysregulation of Histone Transcripts and Nuclear Chromatin

AR DNA-binding protein 43 (TDP-43) is normally a nuclear RNA-binding protein that exhibits a range of functions including regulation of alternative splicing, RNA trafficking, and RNA stability. However, in amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration with TDP-43 inclusions (FTLD-TDP), TDP-43 is abnormally phosphorylated, ubiquitinated, and cleaved, and is mislocalized to the cytoplasm where it forms distinctive aggregates. We previously developed a mouse model expressing human TDP-43 with a mutation in its nuclear localization signal (ΔNLS-hTDP-43) so that the protein preferentially localizes to the cytoplasm. These mice did not exhibit a significant number of cytoplasmic aggregates, but did display dramatic changes in gene expression as measured by microarray, suggesting that cytoplasmic TDP-43 may be associated with a toxic gain-of-function. Here, we analyze new RNA-sequencing data from the ΔNLS-hTDP-43 mouse model, together with published RNA-sequencing data obtained previously from TDP-43 antisense oligonucleotide (ASO) knockdown mice to investigate further the dysregulation of gene expression in the ΔNLS model. This analysis reveals that the transcriptomic effects of the overexpression of the ΔNLS-hTDP-43 transgene are likely due to a gain of cytoplasmic function. Moreover, cytoplasmic TDP-43 expression alters transcripts that regulate chromatin assembly, the nucleolus, lysosomal function, and histone 3’ untranslated region (UTR) processing. These transcriptomic alterations correlate with observed histologic abnormalities in heterochromatin structure and nuclear size in transgenic mouse and human brains

Dynamic modelling of electrooptically modulated vertical compound cavity surface emitting semiconductor lasers

A generalized rate equation model is used to simulate the interrelated amplitude and frequency modulation properties of Electrooptically Modulated Vertical Compound Cavity Surface Emitting Semiconductor Lasers in both large and small signal modulation regimes. It is shown that the photon lifetime in the modulator subcavity provides the ultimate limit for the 3 dB modulation cutoff frequency. It is shown that there is an optimum design (number of periods) of both the intermediate and top multistack reflectors to maximise the large-signal modulation quality