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Femtosecond pump-terahertz probe studies of carrier dynamics in semi-insulating GaAs have been investigated in detail for various pump powers. It is observed that, at high pump powers, the reflection peaks flip to the opposite polarity and dramatically enhance as the pump arrival time approaches the reflected wave of the terahertz pulse. The abnormal polarity-flip and enhancement can be interpreted by the pump-induced enhancement in the photoconductivity of GaAs and half-wave loss. Moreover, the carrier relaxation processes and surface states filling in GaAs are also studied in these measurements. [ABSTRACT FROM AUTHOR]

The spatiotemporal and spectral characteristics of ultrawide-band terahertz pulses after passing through a Fresnel lens are studied by using the scalar diffraction theory. The simulation shows that the transmitted terahertz waveforms compress with increasing propagation distance, and the multi-frequency focusing phenomenon at different focal points is observed. Additionally, the distribution of terahertz fields in a plane perpendicular to the axis is also discussed, and it is found that the diffraction not only induces focusing on-axis but also inhibits focusing at off-axis positions. Therefore, the Fresnel lens may be a useful alternative approach to being a terahertz filter. Moreover, the terahertz pulses travelling as a basic mode of a Gaussian beam are discussed in detail. [ABSTRACT FROM AUTHOR]

The third-order nonlinear optical properties of water-soluble Cu2-xSe nanocrystals are studied in the near infrared range of 700–980 nm using a femtosecond pulsed laser by the Z-scan technique. It is observed that the nonlinear optical response of Cu2-xSe nanocrystals is sensitively dependent on the excitation wavelength and exhibits the enhanced nonlinearity compared with other selenides such as ZnSe and CdSe. The W-shaped Z-scan trace, a mixture of the reversed saturated absorption and saturated absorption, is observed near the plasmon resonance band of Cu2-xSe nanocrystals, which is attributed to the state-filling of free carriers generated by copper vacancies (self-doping effect) of Cu2-xSe nanocrystals as well as the hot carrier thermal effect upon intense femtosecond laser excitation. The large nonlinear optical response and tunable plasmonic band make Cu2-xSe nanocrystals promising materials for applications in ultra-fast all-optical switching devices as well as nonlinear nanosensors. [ABSTRACT FROM AUTHOR]

Utilizing a polarization sensitive terahertz detection method where the detector is rotated by either 0deg or 90deg to measure the electric field Ep,s(t) of each polarization component, we have characterized the properties of split ring resonators. The strong polarization dependence of the bianisotropic-circular-current-driven and linear-polarization-induced resonances is in excellent agreement with the simulation when the p-polarized terahertz transmission is measured. However, these electromagnetic responses vanish when the s-polarized terahertz transmission is measured. There is only a transmission minimum at 1.64 THz and the terahertz polarization rotation angle of about 90deg is observed. The polarized terahertz transmission amplitudes and spectra detected at orthogonal orientations show that these behaviours are probably attributed to the birefringent effect of the sample. [ABSTRACT FROM AUTHOR]

The optical properties of four kinds of lubricating greases (urea, lithium, extreme pressure lithium, molybdenum disulfide lithium greases) with different NLGL (National Lubricant Grease Institute of America) numbers were investigated using terahertz time-domain spectroscopy. Greases with different NLGL grades have unique spectral features in the terahertz range. Comparison of the experimental data with predictions based on Lorentz--Lorenz theory exhibited that the refractive indices of each kind of lubricating grease were dependent on the their consistency. In addition, molybdenum disulfide (MoS2) as a libricant additive shows strong absorption from 0.2 to 1.4 THz, leading to higher absorption of MoS2-lithium grease than that of lithium grease. [ABSTRACT FROM AUTHOR]

A recently introduced ray-tracing method is adopted to study the propagation characteristics of whistler-mode chorus during different geomagnetic activities by using a global core plasma density model. Numerical calculations show that chorus waves tend to settle on a preferable magnetic shell L in the vicinity of the plasmapause. During high geomagnetic activity, the plasmapause position moves inward close to the Earth and chorus trajectories move inward together with plasmapause. The trajectory move closer to the plasmapause as 9 increases. Chorus wave with lower frequencies will reflect multiple times while chorus wave with higher frequencies reflect once at the plasmapause before settling on the vicinity of the plasmapause. The current results present a first detailed study on the propagation characteristics of chorus during geomagnetic activities, and may account for the observation that chorus tends to be present in the vicinity of the plasmapause. [ABSTRACT FROM AUTHOR]

In order to predict the actual quantity of non-bulk GaAs layers after long-time homoepitaxy on GaAs (001) by theoretical calculation, a half-terrace diffusion model based on thermodynamics is used to calculate the ripening time of GaAs layers to form a flat morphology in annealing. To verify the accuracy of the calculation, real space scanning tunneling microscopy images of GaAs surface after different annealing times are obtained and the roughness of the GaAs surface is measured. The results suggest that the half terrace model is an accurate method with a relative error of about 4.1%. [ABSTRACT FROM AUTHOR]

Metal structures with high optical transparency and conductivity are of great importance for practical applications in optoelectronic devices. Here we investigate the transparency response of a continuous metal film sandwiched by double plasmonic nanoparticle arrays. The upper nanoparticle array shows efficient light trapping of the incident field, acting as a light input coupler, and the lower nanoparticle array shows a light release gate opening at the other side, acting as the light output coupler. The strong near-field light-matter interactions of the nano-scale separated plasmonic nanoparticles, the excitation of surface plasmon waves of the metal film, and their cooperative coupling effects result in broadband scattering cancellation and near-unity transparency (up to 96%) in the optical regime. The transparency response in such a structure can be efficiently modified by varying the gap distance of adjacent nanoparticles, dielectric environments, and the distance between the plasmonic array and the metal film. This motif may provide a new alternative approach to obtain transparent and highly conducting metal structures with potential applications in transparent conductors, plasmonic filters, and highly integrated light input and output components. [ABSTRACT FROM AUTHOR]

After approximately half a century of development, HgCdTe infrared detectors have become the first choice for high performance infrared detectors, which are widely used in various industry sectors, including military tracking, military reconnaissance, infrared guidance, infrared warning, weather forecasting, and resource detection. Further development in infrared applications requires future HgCdTe infrared detectors to exhibit features such as larger focal plane array format and thus higher imaging resolution. An effective approach to develop HgCdTe infrared detectors with a larger array format size is to develop the small pixel technology. In this article, we present a review on the developmental history and current status of small pixel technology for HgCdTe infrared detectors, as well as the main challenges and potential solutions in developing this technology. It is predicted that the pixel size of long-wave HgCdTe infrared detectors can be reduced to 5 μm, while that of mid-wave HgCdTe infrared detectors can be reduced to 3 μm. Although significant progress has been made in this area, the development of small pixel technology for HgCdTe infrared detectors still faces significant challenges such as flip-chip bonding, interconnection, and charge processing capacity of readout circuits. Various approaches have been proposed to address these challenges, including three-dimensional stacking integration and readout circuits based on microelectromechanical systems. [ABSTRACT FROM AUTHOR]

We propose a theoretical scheme to speed up adiabatic population transfer in a Josephson artificial qutrit by transitionless quantum driving. At a magic working point, an effective three-level subsystem can be chosen to constitute our qutrit. With Stokes and pump driving, adiabatic population transfer can be achieved in the qutrit by means of stimulated Raman adiabatic passage. Assisted by a counterdiabatic driving, the adiabatic population transfer can be sped up drastically with accessible parameters. Moreover, the accelerated operation is flexibly reversible and highly robust against decoherence effects. Thanks to these distinctive advantages, the present protocol could offer a promising avenue for optimal coherent operations in Josephson quantum circuits. [ABSTRACT FROM AUTHOR]

We present here an adaptive control scheme with a feedback delay to achieve elimination of synchronization in a large population of coupled and synchronized oscillators. We validate the feasibility of this scheme not only in the coupled Kuramoto’s oscillators with a unimodal or bimodal distribution of natural frequency, but also in two representative models of neuronal networks, namely, the FitzHugh–Nagumo spiking oscillators and the Hindmarsh–Rose bursting oscillators. More significantly, we analytically illustrate the feasibility of the proposed scheme with a feedback delay and reveal how the exact topological form of the bimodal natural frequency distribution influences the scheme performance. We anticipate that our developed scheme will deepen the understanding and refinement of those controllers, e.g. techniques of deep brain stimulation, which have been implemented in remedying some synchronization-induced mental disorders including Parkinson disease and epilepsy. [ABSTRACT FROM AUTHOR]

The laser-pumped potassium spin-exchange relaxation free (SERF) magnetometer is the most sensitive detector of magnetic field and has many important applications. We present the experimental results of our potassium SERF magnetometer. A pump–probe approach is used to identify the unique spin dynamics of the atomic ensemble in the SERF regime. A single channel sensitivity of 8 f·THz−1/2 is achieved with our SERF magnetometer. [ABSTRACT FROM AUTHOR]

Owing to its unique photothermal initiation mode, laser ignition has been considered as one of the most promising initiation methods for the next generation of initiators and pyrotechnics. Unfortunately, the wide application of laser ignition has been prevented by its stubbornly high initiating energy. With the benefit of a unique two-dimensional (2D) layered structure, graphene oxide has been reported to be effective in reducing the initiating energy for laser ignition. However, due to the intrinsic drawbacks of graphene oxide, a further reduction in initiating energy is still a challenging task. Notably, a core–shell structure is a very attractive framework for the design of functional materials owing to its versatility in regulating the properties of diverse components. Herein, we have designed a graphene-based core–shell structure by the in-situ formation of a uniform coating layer on the surface of individual graphene oxide sheets. The 3-aminophenol/formaldehyde resin coating layer will contribute to increases in light absorbance and energy density, which endow the surface coated graphene oxide with much improved photothermal properties. Accordingly, through use as the energy converter of the laser ignition device, a freestanding membrane of surface-coated graphene oxide is able to effectively enhance the temperature rise during laser irradiation and reduce the initiating energy for laser ignition. Such a strategy of designing a suitable core–shell structure will not only serve to further improve laser ignition, but also shed light on the development of 2D materials in different fields. [ABSTRACT FROM AUTHOR]

A miniature quad-channel optically pumped atomic magnetometer (OPM) has been developed based on the spin-exchange relaxation-free (SERF) mechanism. With a vapor cell of size 8 mm×8 mm×8 mm, we have incorporated four SERF magnetometer channels, which provides sufficient spatial resolution for magnetoencephalography (MEG). The four channels share the same laser beam for the best cancellation of common mode noise due to laser fluctuations. With gradient measurement, the sensitivities of the four sensors are better than 6 fT/Hz1/2, which is also good enough for MEG measurement. The vapor cell is heated to 160 °C by a novel nonmagnetic current-heating structure. Our sensor with high spatial resolution and compact size is particularly suitable for MEG systems. [ABSTRACT FROM AUTHOR]

We present an alternate adiabatic evolution for the Deutsch—Jozsa problem. The biggest difference of our adiabatic evolution constructed here with those appearing before is that an alternate initial Hamiltonian is used for the adiabatic evolution, with which the evolution task can be finished in O(1) time complexity. Our construction mostly resembles the one discussed by Das et al. [Phys. Rev. A 65 (2002) 062310], except for the initial system Hamiltonian of the adiabatic algorithm. [ABSTRACT FROM AUTHOR]

Silver nanocluster embedded ZnO composite thin film was observed to have an angle-sensitive and fast photovoltaic effect in the angle range from [?]90deg to 90deg, its peak value and the polarity varied regularly with the angle of incidence of the 1.064-mm pulsed Nd:YAG laser radiation onto the ZnO surface. Meanwhile, for each photovoltaic signal, its rising time reached [?]2 ns with an open-circuit photovoltage of [?]2 ns full width at half-maximum. This angle-sensitive fast photovoltaic effect is expected to put this composite film a candidate for angle-sensitive and fast photodetector. [ABSTRACT FROM AUTHOR]