Zuoliang Liu

Growth and optical properties of a new nonlinear Na 3 La 9 O 3 (BO 3 ) 8 crystal

New nonlinear crystals Na(3)La(9)O(3)(BO(3))(8) (abbreviated as NLBO) with desired morphologies, high quality and weight exceeding 40g have been grown along different directions, such as [001], [110], and [100], by top-seeded solution growth(TSSG) method. The refractive indices were accurately measured over the full transmission range, and the second-order nonlinear optical coefficients were determined by the Maker fringe technique. The optimal phase-matching (PM) conditions and the corresponding effective nonlinear coefficient were calculated for second harmonic generation (SHG) at different wavelengths. In order to confirm the correctness of our calculation, we also performed the SHG experiments under 1064 and 800 nm pumping, respectively. In addition, we directly compared the SHG performance of NLBO with that of LBO under the same experimental conditions with the 1064 nm pumping source. As the results, a conversion efficiency of 58.3% at 532 nm was obtained for NLBO, and whereas only 21.5% was obtained for LBO, indicating that NLBO is a highly attractive nonlinear material for frequency conversion of pulses into the visible and ultraviolet.

Kinetic Alfven waves driven by velocity shear

Considering the effect of the finite ion gyroradius, the kinetic Alfven wave in an anisotropic medium driven by a parallel velocity flow was investigated and the full dispersion relation was given. In deducing the dispersion relation, the coupling between electrostatic and electromagnetic oscillations, effects of the resonant electrons and the longitudinal motion of ions are considered. Based on the analytical and numerical calculations, two instability boundaries are found. They are 1 νA2/(Ti/mi). Resonant electrons serve as the main energy source in these two regimes, while the ion longitudinal motion only suppresses the mode in the second regime. In the boundary layer of the magnetopause, the temperature anisotropy also modifies the instability by lowering the frequency and reducing the growth rate. The above results show that the low-frequency Alfven waves with the scale of perpendicular wavelengths greater than the ion gyroradius in the magnetopause ...

The coupling mode between Kelvin–Helmholtz and resistive instabilities in compressible plasmas

Using a compressible magnetohydrodynamics (MHD) simulation method, the coupling mode between Kelvin–Helmholtz (K–H) and resistive instabilities has been investigated. It is found that, in compressible plasmas, the coupling mode can take place in a limited range of ambient shear flow velocity, beyond which the coupling mode is stabilized. The flow shear can significantly enhance the growth of the coupling mode. Only in a narrow range of plasma beta, could the coupling mode occur. It is deduced that this kind of coupling mode may appear at Earth’s magnetopause.

Properties of the neutral energetic atoms emitted from Earth’s ring current region

Simulations of energetic neutral atoms (ENA) during the geomagnetic storm main phase have been carried out to provide reliable theoretical foundations for the development of an ENA detector on board the polar satellite of the Chinese Double Star Program (DSP), and to make preparation for the future ENA observational data analyses. In this research, an approximate analytical model for the ring current particle distributions, including the ion loss due to charge exchange processes, has been developed. The simulations have shown that there are two maximum ENA flux regions: The ring current inner boundary region, and the particle precipitation region at the northern and southern poles. The stronger the storms, the lower the particle injection, and the larger the flux of ENA emitted from the ring current region. The ENA detector at advantageous positions can measure the inner boundary of the injection region or the injection front. The ENA detector is able to measure the inhomogeneity of the ring current ions....

Shocks associated with the Kelvin-Helmholtz-resistive instability

In this paper, a new type of shock associated with magnetic reconnection processes has been explored using a compressible magnetohydrodynamics simulation method. The simulations have shown that, when there are strong field-aligned shear flows at the two sides of a current sheet, the coupling mode between Kelvin–Helmholtz and resistive instabilities will appear; further, reflected shocks and incident shocks can be produced at both sides of the boundary layer. Both the reflected shocks and incident shocks are fast shocks, through which the magnetic field strength, density, and temperature all increase sharply, while the plasma velocity decreases steeply. It is expected that some inhomogeneous structures can be formed at plasma boundary layer regions due to the existence of fast field-aligned shear flow driven shocks.

Nonlinear waves in a low-β plasma with cylindrical symmetry

The “Sagdeev potential” is derived from the magnetohydrodynamic equations in a cylindrical coordinate system, and nonlinear electrostatic density waves propagating along the magnetic field in a low-β plasma with cylindrical symmetry are studied. The results show the existence not only of periodic density waves, solitons with a density hump and solitons with a density dip, but also of density shock waves.

Direct laser writing of pyramidal plasmonic structures with apertures and asymmetric gratings towards efficient subwavelength light focusing

Efficient confining of photons into subwavelength scale is of great importance in both fundamental researches and engineering applications, of which one major challenge lies in the lack of effective and reliable on-chip nanofabrication techniques. Here we demonstrate the efficient subwavelength light focusing with carefully engineered pyramidal structures fabricated by direct laser writing and surface metallization. The important effects of the geometry and symmetry are investigated. Apertures with various sizes are flexibly introduced at the apex of the pyramids, the focusing spot size and center-to-sidelobe ratio of which could be improved a factor of ~4 and ~3, respectively, compared with the conical counterparts of identical size. Moreover, two pairs of asymmetric through-nanogratings are conceptually introduced onto the top end of the pyramids, showing significantly improved focusing characteristics. The studies provide a novel methodology for the design and realization of 3D plasmonic focusing with low-noise background and high energy transfer.

Multiple bipolar structure of normal magnetic field at the magnetopause

Abstract We describe how a local plasma structure can be changed by a transverse shear flow using numerical simulation to investigate the disturbance process near the magnetopause. The results show that magnetic field lines are bent by transverse shear flow disturbance near the current sheet region. There are multiple bipolar structures of the normal magnetic field in the numerical simulation. We term this new feature as K-point magnetic reconnection, realistic for discussing space observations.

Transient reconnection caused by the impact and switch-off of a transverse shear flow

It is supposed that local and transient reconnection in the plasma boundary layer can be caused by the impact and switch-off of a single directional transverse shear flow. MHD (magnetohydrodynamic) simulation is used to investigate the reconnection processes in the two cases. It is found that if the inflow is homogeneous, it does not cause reconnection; if the inflow is shearing flow, no matter how great the shear of the flow is, it may cause reconnection either during impacting period or after stop impacting. It is pointed out that the sudden stop of external force may be an important triggering mechanism of energy transformation and reconnection in the plasma boundary layer region.

Nonapotassium trialuminium hexa­phosphate

In the title compound, K9Al3(PO4)6, the anionic substructure is built of interlinked [PO4] and [AlO4] tetrahedra. Each O atom of the [AlO4] tetrahedron is common to a positionally different [PO4] tetrahedron; thus, each [AlO4] tetrahedron is surrounded by four positionally different [PO4] tetrahedra. On the other hand, each [PO4] tetrahedron shares its two O atoms with two positionally different [AlO4] tetrahedra; the other two phosphate O atoms are terminal ones coordinated by K atoms. The terminal O atoms are usually closer to the K atoms than the bridging O atoms between the [AlO4] and [PO4] tetrahedra. There are nine symmetry-independent K atoms in the structure. The coordination numbers of the K atoms are 6 or 7 or 8 up to a distance of 3.31 Å. There are channels in the anionic substructure oriented along the [10] direction that are filled by K atoms.