Output response in orthogonal directions of a He–Ne laser caused by birefringent-external-cavity feedback

The output responses of phase, amplitude, and polarization of light intensity of a He–Ne laser with the birefringent external cavity are presented. All phenomena are observed in two orthogonal directions related to the birefringent element’s orientation, and are studied under weak optical feedback. Experiments are carried out in five available detecting positions. It is found that laser intensities are modulated in the two orthogonal directions simultaneously, with a phase difference dominated by the phase retardation of the birefringence element. The modulation amplitudes are different in the two directions. A special polarization phenomenon is also observed and discussed. This research may provide a potential novel measuring principle for transparent birefringent materials.     

High Carbon-Resistance Ni@CeO<Subscript>2</Subscript> Core–Shell Catalysts for Dry Reforming of Methane

Ni@CeO₂ core–shell catalysts were synthesized via a facile surfactant-assisted hydrothermal method and their catalytic performance in the dry reforming of methane (DRM) reaction was evaluated. A variety of techniques including XRD, N₂ adsorption–desorption, SEM, TEM, TPO, TGA were employed to characterize the prepared or spent catalysts. The encapsulation by the CeO₂ shell, on one side, can restrict the sintering and growth of Ni nanoparticles under harsh reaction conditions. On the other side, compared to the conventional shell material of SiO₂, CeO₂ can provide more lattice oxygens and vacancies, which is helpful to suppress coke deposition. Consequently, the Ni@CeO₂ core–shell catalysts exhibited better catalytic activity and stability in the DRM reaction with respect to the referenced Ni@SiO₂ core–shell catalysts and Ni/CeO₂ supported catalysts.     

Grand Canonical Ensemble Interpretation for Charged Particle Quantum Tunneling Radiation

In this paper, we present a grand canonical ensemble interpretation for the massive charged particles tunneling from a charged black hole. The probability distribution function corresponding the emission shell system is derived in details, and the expression is same as the tunneling rate in Parikh-Wilzeck framework. With this result, the statistical significance of the quantum tunneling radiation is discussed.     

Enhancement of thermal stability and photoluminescent performance of blue light emitting material by incorporating adamantane moieties into carbazole system

A facile route to improve photoluminescent performance and service lifetime of a promising blue light emitting material is reported and demonstrated here using a copolymer system of N-(2-ethylhexyl)-2,7-carbazole (Cz) and 1,3,5,7-tetrakis- (4-bromophenyl) adamantane (TBA). The copolymers were successfully synthesized by palladium-catalyzed Suzuki coupling reactions. Structure and molecular weight of the materials were characterized by FT-IR and ¹H-NMR spectroscopies, elemental analysis and gel permeation chromatography. The influence of adamantane content on the thermal stability and photoluminescent performance of the synthesized copolymers was investigated in detail. DSC results showed that glass transition temperature increased dramatically, from 68°C for neat carbazole, to 88°C, 120°C and 152°C, after the addition of 10%, 20%, and 30% TBA, respectively. The same trend was found when thermal decomposition temperature at 5% weight loss was evaluated from TGA data. Importantly, this increased stability can be extended to thermo-optical performance, with the Cz-TBA system showing higher color purity and stronger emission intensity within blue light wavelength than carbazole alone. Nevertheless, measurements of emitting spectral stability at a broader temperature range (100–200°C) and photoluminescence quantum yield suggested that there is a delicate trade-off between the performance and adamantane content.     

High-birefringence nematic liquid crystal for broadband THz applications

Liquid crystals (LCs) have been studied extensively in the visible range for their dielectric tunability, and the characterisation in the terahertz (THz) range has gained increasing interest due to the need for active THz modulation and switching devices. In this paper, we use THz time-domain spectroscopy to measure the frequency-dependent birefringence and the absorption coefficient of a number of commercial and non-commercial nematic LCs, including E7, BL037, MDA-98-1602, LCMS-107, GT3-23001 and 1825, over a range of bias voltages at room temperature. Furthermore, several basic components of LC mixture are analysed to establish their contributions to birefringence and theoretical model is used to fit the absorption spectra. The large tunability and low loss measured for a range of samples show that the LCs are useful tunable dielectrics for compact, efficient and broadband THz devices.     

A polynomial approximation for arbitrary functions

We describe an expansion of Legendre polynomials, analogous to the Taylor expansion, for approximating arbitrary functions. We show that the polynomial coefficients in the Legendre expansion, and thus, the whole series, converge to zero much more rapidly compared to those in the Taylor expansion of the same order. Furthermore, using numerical analysis with a sixth-order polynomial expansion, we demonstrate that the Legendre polynomial approximation yields an error at least an order of magnitude smaller than that of the analogous Taylor series approximation. This strongly suggests that Legendre expansions, instead of Taylor expansions, should be used when global accuracy is important.     

Material growth and device fabrication of terahertz quantum-cascade laser based on bound-to-continuum structure

The terahertz quantum-cascade laser （THz QCL） based on bound-to-continuum structure is demonstrated. The X-ray diffraction measurement of the material shows a high crystalline quality of the active region. A THz QCL device was fabricated with semi-insulating surface-plasmon waveguide. The test device is lasing at about 3 THz and operating up to 60 K. It shows a single frequency property under different drive currents and temperatures. At 9 K, the maximum output power is greater than 2 mW with a threshold current density of 159 A/cm2.