Directly generating vortex beams in the second harmonic by a spirally structured fundamental wave

Based on nonlinear wave mixing, we experimentally propose a scheme for directly generating optical orbital angular momentum(OAM) by a spirally structured fundamental wave interacting with a nonlinear medium, in which the nonlinear susceptibilities are homogenous. In the experiment, the second-harmonic generation of a fundamental wave carrying positive(negative) integers and fractional OAM states was investigated. This study presents a convenient approach for dynamic control of OAM of vortex beams, which may feature their applications in optical manipulation and optical communication.

On the Fundamental Mode Love Wave in Devices Incorporating Thick Viscoelastic Layers

A detailed investigation is presented for Love waves （LWs） with thick viscoelastic guiding layers. A theoretical calculation and an experiment are carried out for LW devices incorporating an SU-8 guiding layer, an ST-90° X quartz substrate and two 28-μm periodic interdigital transducers. Both the calculated and the measured results show an increase in propagation velocity when h / λ〉0.05. The measured insertion loss of LWs is consistent with the calculated propagation loss. The insertion loss of bulk waves is also measured and is compared with that of LWs.

Frequency domain fundamental solutions for a poroelastic half-space

In frequency domain, the fundamental solutions for a poroelastic half-space are re-derived in the context of Biot＇s theory. Based on Biot＇s theory, the governing field equations for the dynamic poroelasicity are established in terms of solid displacement and pore pressure. A method of potentials in cylindrical coordinate system is proposed to decouple the homogeneous Biot＇s wave equations into four scalar Helmholtz equations, and the general solutions to these scalar wave equations are obtained. After that, spectral Green＇s functions for a poroelastic full-space are found through a decomposition of solid displacement, pore pressure, and body force fields. Mirror-image technique is then applied to construct the half-space fundamental solutions.Finally, transient responses of the half-space to buried point forces are examined.

Electron Cyclotron Harmonic Wave Heating in Tokamak Plasmas with Different Polarization Modes

Electron cyclotron heating on HL-2A has been simulated by TORAY-GA with a second harmonic extraordinary wave and a fundamental ordinary wave. The results show that the wave absorption of the second harmonic extraordinary wave is better than that of the fundamental ordinary wave. In order to understand the interaction mechanism between electrons and the two different polarization modes, the energy exchange between electrons and the two modes are theoretically analyzed, and it is found that the coupling intensity described by the Bessel function and different polarizations of the two modes are the main reasons leading to the above phenomenon. The theoretical results of this study fit well with the simulated and numerical results.