We analyze GaInN based light emitting diodes emitting in the range of 400-550nm using a new intensity-quantitative spectroscopic cathodoluminescence mapping method. Spectroscopic information of arbitrary sample locati...
详细信息
We analyze GaInN based light emitting diodes emitting in the range of 400-550nm using a new intensity-quantitative spectroscopic cathodoluminescence mapping method. Spectroscopic information of arbitrary sample locations is generated from sequences of quantitative image scans. From the temperature dependence of the intensity, we derive thermal activation energies of the dominant loss processes. Those compare well with the hole binding energies in the piezoelectric and quantized quantum well structures.
We report the observation of a coherent multimode instability in quantum cascade lasers (QCLs), which is driven by the same fundamental mechanism of Rabi oscillations as the elusive Risken-Nummedal-Graham-Haken (RNGH)...
详细信息
We report the observation of a coherent multimode instability in quantum cascade lasers (QCLs), which is driven by the same fundamental mechanism of Rabi oscillations as the elusive Risken-Nummedal-Graham-Haken (RNGH) instability predicted 40years ago for ring lasers. The threshold of the observed instability is significantly lower than in the original RNGH instability, which we attribute to saturable-absorption nonlinearity in the laser. Coherent effects, which cannot be reproduced by standard laser rate equations, can play therefore a key role in the multimode dynamics of QCLs, and in lasers with fast gain recovery in general.
Ultrafast mid-infrared pump-probe experiments are used to study gain dynamics and transport processes in quantum cascade lasers below and above threshold. We observe for the first time how stimulated emission drives t...
详细信息
ISBN:
(纸本)1557528349
Ultrafast mid-infrared pump-probe experiments are used to study gain dynamics and transport processes in quantum cascade lasers below and above threshold. We observe for the first time how stimulated emission drives the current through the cascade heterostructure.
We report a series of femtosecond pump-probe measurements on quantum cascade lasers operating below and above threshold; the gain recovery dynamics reveal how quantum stimulated emission drives the current through the...
详细信息
ISBN:
(纸本)1424411742
We report a series of femtosecond pump-probe measurements on quantum cascade lasers operating below and above threshold; the gain recovery dynamics reveal how quantum stimulated emission drives the current through the cascade heterostructure, which we refer to as photon-driven transport.
We report on temperature dependence of the radial breathing mode (RBM) frequency and its decay time in single walled carbon nanotubes (SWCNTs), which were studied by the femtosecond pump and probe technique. With incr...
详细信息
ISBN:
(纸本)1424411742
We report on temperature dependence of the radial breathing mode (RBM) frequency and its decay time in single walled carbon nanotubes (SWCNTs), which were studied by the femtosecond pump and probe technique. With increasing temperature, we found out that the RBM frequency and phonon decay time shows on abnormal dramatic change around 70℃ for a certain type of carbon nanotubes, which may be originated from the surfactant effect.
The largest eigenvalue of the adjacency matrix of a network plays an important role in several network processes (e.g., synchronization of oscillators, percolation on directed networks, and linear stability of equilib...
The largest eigenvalue of the adjacency matrix of a network plays an important role in several network processes (e.g., synchronization of oscillators, percolation on directed networks, and linear stability of equilibria of network coupled systems). In this paper we develop approximations to the largest eigenvalue of adjacency matrices and discuss the relationships between these approximations. Numerical experiments on simulated networks are used to test our results.
Time‐resolved mid‐infrared pump‐probe measurements in an operating quantum cascade laser below and above threshold reveal gain recovery dynamics to be driven by transport through the quantum cascade structure with ...
Time‐resolved mid‐infrared pump‐probe measurements in an operating quantum cascade laser below and above threshold reveal gain recovery dynamics to be driven by transport through the quantum cascade structure with two components: relaxation within a stage on a sub‐picosecond scale and transport between stages on a picosecond scale. The fast recovery corresponds to resonant tunneling from the injector ground state into the upper lasing state, and is found to be incoherent due to strong dephasing via intraband electron‐electron scattering. The slower component corresponds to miniband superlattice transport. Both components have been studied as a function of bias and temperature.
We investigate the transport properties of superconducting films with periodic arrays of in-plane magnetized micromagnets. Two different magnetic textures are studied: a square array of magnetic bars and a close-packe...
详细信息
We investigate the transport properties of superconducting films with periodic arrays of in-plane magnetized micromagnets. Two different magnetic textures are studied: a square array of magnetic bars and a close-packed array of triangular microrings. As confirmed by magnetic force microscopy imaging, the magnetic state of both systems can be adjusted to produce arrays of almost pointlike magnetic dipoles. By carrying out transport measurements with ac drive, we observed experimentally a recently predicted ratchet effect induced by the interaction between superconducting vortices and the magnetic dipoles. Moreover, we find that these magnetic textures produce vortex-antivortex patterns, which have a crucial role in the transport properties of this hybrid system.
We present our femtosecond optical pump-probe studies of proximized ferromagnet-superconductor nanobilayers. The weak ferromagnetic nature of a thin NiCu film makes it possible to observe the dynamics of the nonequili...
We present our femtosecond optical pump-probe studies of proximized ferromagnet-superconductor nanobilayers. The weak ferromagnetic nature of a thin NiCu film makes it possible to observe the dynamics of the nonequilibrium carriers through the near-surface optical reflectivity change measurements. The subpicosecond biexponential reflectivity decay has been identified as electron-phonon Debye and acoustic phonon relaxation times, and the decay of Debye phonons versus temperature dependence was used to evaluate the electron-phonon coupling constants for both the pure Nb and proximized Nb∕NiCu heterostructures down to low temperatures. We have also demonstrated that the NiCu overlay on top of Nb dramatically reduced the slow, bolometric component of the photoresponse component, making such bilayers attractive for future radiation detector applications.
The evolution of dense aluminum and carbon plasmas produced by laser irradiation of 500−μm-diam semicylindrical targets was studied using soft x-ray laser interferometry. Plasmas created heating the cavity walls with...
详细信息
The evolution of dense aluminum and carbon plasmas produced by laser irradiation of 500−μm-diam semicylindrical targets was studied using soft x-ray laser interferometry. Plasmas created heating the cavity walls with 120−ps—duration optical laser pulses of ∼1×1012Wcm−2 peak intensity were observed to expand and converge on axis to form a localized high-density plasma region. Electron density maps were measured using a 46.9−nm-wavelength tabletop capillary discharge soft x-ray laser probe in combination with an amplitude division interferometer based on diffraction gratings. The measurements show that the plasma density on axis exceeds 1×1020cm−3. The electron density profiles are compared with simulations conducted using the hydrodynamic code HYDRA, which show that the abrupt density increase near the axis is dominantly caused by the convergence of plasma generated at the bottom of the groove during laser irradiation.
暂无评论