Unidirectional control of optically induced spin waves

Unidirectional control of optically induced spin waves in a rare-earth iron garnet crystal is demonstrated. We observed the interference of two spin-wave packets with different initial phases generated by circularly polarized light pulses. This interference results in unidirectional propagation if the spin-wave sources are spaced apart at 1/4 of the wavelength of the spin waves and the initial phase difference is set to pi/2. The propagating direction of the spin wave is switched by the polarization helicity of the light pulses. Moreover, in a numerical simulation, applying more than two spin-wave sources with a suitable polarization and spot shape, arbitrary manipulation of the spin wave by the phased array method was replicated

Polarization and Arriving Direction of VLF Emissions

Polarization and direction of arrival of VLF emissions have been observed at Syowa Station in the Antarctic by a combination of a vertical antenna and a crossed loop antenna with their planes oriented in geomagnetic E-W and N-S directions. The results obtained with a polarimeter show that the emissions at 750Hz, 12kHz and 25kHz were roughly left-hand polarization waves (whistler mode) in all seasons, when one viewed towards the observation site on the earth\u27s magnetic field. But there seemed to be some seasonal variations in the ratio of right-hand polarization waves to left-hand ones. A pronounced example is that the emission at 25kHz was linearly polarized in winter (July and August). The oscillographic patterns obtained with a direction finder seem to indicate that the emission at 12kHz arrived simultaneously from various directions, and that the emission was almost elliptically polarized. But in a few cases, the emission seemed to come down roughly from a vertical direction along a geomagnetic field line, and to be circularly polarized

Lattice Boltzmann simulation of nucleate pool boiling in saturated liquid

First published in Communications in Commun. Comput. Phys. in No. 5, 9 (2011), published by Global Science PressA thermal lattice Boltzmann method (LBM) for two-phase fluid flows in nucleate pool boiling process is proposed. In the present method, a new function for heat transfer is introduced to the isothermal LBM for two-phase immiscible fluids with large density differences. The calculated temperature is substituted into the pressure tensor, which is used for the calculation of an order parameter representing two phases so that bubbles can be formed by nucleate boiling. By using this method, two-dimensional simulations of nucleate pool boiling by a heat source on a solid wall are carried out with the boundary condition for a constant heat flux. The flow characteristics and temperature distribution in the nucleate pool boiling process are obtained. It is seen that a bubble nucleation is formed at first and then the bubble grows and leaves the wall, finally going up with deformation by the buoyant effect. In addition, the effects of the gravity and the surface wettability on the bubble diameter at departure are numerically investigated. The calculated results are in qualitative agreement with other theoretical predictions with available experimental data.ArticleCommunications in Computational Physics. 9(5):1347-1361 (2011)journal articl

Helical dichroism for hybridized quadrupole plasmon modes in twisted metal nanorods

Helical dichroism (HD), based on the interaction between chiral plasmonic nanostructures and light with orbital angular momentum (OAM), has attracted researchers in a wide range of fields from the viewpoint of fundamental physics and applications. However, the relation between the HD and the excited plasmon modes has been poorly understood in experiments. Because of the weak chiral interaction between the chiral structures and OAM light, the structure size must be much larger than the incident light wavelength to obtain sufficient HD signal, resulting in the complex superposition of higher-order plasmon modes. Recently, we experimentally demonstrated that a twisted gold nanorod dimer, one of the simplest 3D chiral plasmonic structures, exhibits giant circular dichroism due to strong plasmon coupling between the nanorods, followed by the hybridization of dipole mode. In this study, we reveal that the HD of this nanorod dimer appears due to the hybridization of quadrupole plasmon mode rather than dipole mode. Furthermore, the measurement of the HD signal can be achieved by using the array of the twisted dimers. The dependence of the HD on the incident light wavelength exhibits that the HD sign changes around the quadrupole plasmon resonance, which is in good agreement with the simulation. These results pave the way to novel insights into the profound understanding of the light-matter interaction with respect to angular momentum.Comment: 10 pages, 3 figure