Description: Multicore quantum cascade lasers with large cavities show low optical losses, high saturation intensity, and low beam divergence. We present a four active core laser based on InGaAs–AlInAs material system emitting at 10.5 μm. To improve thermal conductance, InP interstacks were used to separate active regions. Selective lateral etching of the active regions was used to reduce optical losses. Peak powers up to 4.6 W, average powers up to 310 mW, and wall-plu...
Description: In this paper an interferometric setup called “thermoelastic microscopy” has been used to measure the vibration response of the semiconductor cantilevers under modulated laser thermal source. The small vibration amplitude has been detected well below 10 pm magnitude in accurate adjustment conditions. The results showed that experimental responses have a good agreement with the theoretical ones. Also from the analysis we could conclude that the signal amplitu...
Description: We have explored the low energy charge dynamics of charge-ordered Nd0.5Ca0.5MnO3 and Ba-doped Nd0.5Ca0.48Ba0.02MnO3 manganite thin films by recording the complex optical spectra using terahertz time-domain spectroscopy. The extracted frequency- and temperature-dependent optical conductivity (σ) and dielectric constant (ε1) show distinct features at Néel’s ordering and the charge-ordering temperatures (TN and TCO) . We found that the Ba-doping induced cation...
Description: Previous studies of phase mixing of ion cyclotron (IC), Alfvénic, waves in the collisionless regime have established the generation of parallel electric field and hence acceleration of electrons in the regions of transverse density inhomogeneity. However, outstanding issues were left open. Here we use the 2.5 D, relativistic, fully electromagnetic particle-in-cell code and an analytic magnetohydrodynamic (MHD) formulation, to establish the following points: ...
Description: We propose a fiber-based system aimed at generating radially and azimuthally polarized beams over spectral ranges of several tens of nanometers. The device is either adaptable to polychromatic sources such as supercontinuum fiber lasers or to tunable ones optical parametric oscillator, laser diode, etc. . A preliminary version of the system has been engineered to work in the visible portion of the spectrum. The concept proposed here can be adapted to the in...
Description: Ion transport in cationically and anionically functionalized polyacetylene ionomers, PAC and PAA, respectively, was investigated by analyzing the impedance responses of thin film Au∣ionomer∣Au sandwich configurations. Samples were measured over a frequency range of 10−2–106 Hz and a temperature range of 298–398 K. Electrode polarization at low frequencies and dispersion due to ion hopping at higher frequencies were observed. The impedance data were analyzed ...
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Description: We demonstrate the fabrication of optically active uniform InGaAs quantum dot arrays by combining nanosphere lithography and bromine ion-beam-assisted etching on a single InGaAs/ GaAs quantum well. A wide range of lateral dot sizes was achieved from an oxygen plasma nanosphere resizing process. The increased lateral confinement of carriers in the dots results in low temperature photoluminescence blueshifts from 0.5 to 11 meV. Additional quantization was achi...
Description: Recently, complete chaotic synchronization in coupled systems has been well studied. In this paper, we study complete synchronization in coupled periodic oscillators with diffusive and gradient couplings. Eight typical types of critical curve for the transverse Lyapunov exponent of standard mode, which give rise to different synchronization-desynchronization patterns, are classified. All possible desynchronous behaviors including steady state, periodic state...
Description: We propose a method for the evaluation of magnetic exchange couplings based on noncollinear spin density functional calculations. The method employs the second derivative of the total Kohn–Sham energy of a single reference state, in contrast to approximations based on Kohn–Sham total energy differences. The advantage of our approach is twofold: It provides a physically motivated picture of the transition from a low-spin to a high-spin state, and it utilizes ...
Description: Low temperature photoluminescence and reflectance measurements on epitaxially lifted-off (ELO) bulk GaAs and GaAs/AlGaAs multiple quantum wells (MQWs) bonded to Si and MgO substrates are reported. Photoluminescence measurements indicate no strain at room temperature for the ELO bulk GaAs film but show biaxial strain at 10 K. Si-bonded films undergo tensile strain, while films with MgO host substrates experience compressive strain. Reflectance measurements at...
Description: High-speed inline digital holographic cinematography is used for studying turbulent diffusion of slightly buoyant 0.5–1.2 mm diameter diesel droplets and 50 μm diameter neutral density particles. Experiments are performed in a 50×50×70 mm3 sample volume in a controlled, nearly isotropic turbulence facility, which is characterized by two dimensional particle image velocimetry. An automated tracking program has been used for measuring velocity time history of ...
Description: We present superparamagnetic clusters of structurally highly disordered Co–Zn–O created by high fluence Co ion implantation into ZnO (0001) single crystals at low temperatures. This secondary phase cannot be detected by common x-ray diffraction but is observed by high-resolution transmission electron microscopy. In contrast to many other secondary phases in a ZnO matrix, it induces low-field anomalous Hall effect and is thus a candidate for magnetoelectronics applications.
Description: In this paper, we study the charge dynamics in ionic polymer metal composites (IPMCs) in response to a voltage difference applied across their electrodes. We use the Poisson–Nernst–Planck equations to model the time evolution of the electric potential and the concentration of mobile counterions. We present an analytical solution of the nonlinear initial-boundary value problem by using matched asymptotic expansions. We determine the charge and electric potent...
Description: A fiber optic reflectometer (FOR) technique featuring a single fiber probe is investigated for its feasibility of measuring the bubble velocity, diameter, and void fraction in a multiphase flow. The method is based on the interference of the scattered signal from the bubble surface with the Fresnel reflection signal from the tip of the optical fiber. Void fraction is obtained with a high accuracy if an appropriate correction is applied to compensate the unde...
Description: A novel scheme of transferring cold atoms in a double magneto-optical trap (MOT) system has been experimentally demonstrated. Cold cesium atoms trapped in a vapor-cell MOT are efficiently transferred to an ultrahigh-vacuum (UHV) MOT by a continuous-wave divergent Gaussian transfer laser beam. When large red detuning and moderate intensity are adopted for the transfer laser beam, enhancement of the recapturing of atoms in the UHV MOT is clearly observed. Usin...
Description: We propose and demonstrate a displacement control method at the subnanometric scale based on a Michelson interferometer combined with a polarimeter and a phase-locked loop electronic board. Step by step displacements with a step value of 5 nm are presented. A repeatability of 0.47 nm is obtained from back and forth displacements over 1 μm range. We show that a residual ellipticity of less than 10° on the polarization state leads to a positioning error of les...
Description: By coupling a comprehensive tunable vacuum ultraviolet (VUV) laser system to a velocity-mapped ion imaging apparatus, we show that high-resolution high-n Rydberg tagging time-of-flight (TOF) measurements of nascent atomic photofragments formed by laser photodissociation can be made using single-photon VUV laser photoexcitation. To illustrate this single-photon Rydberg tagging TOF method, we present here the results of the VUV laser high-n Rydberg tagging TOF...