Consistent modelling of wind turbine noise propagation from source to receiver.

The unsteady nature of wind turbine noise is a major reason for annoyance. The variation of far-field sound pressure levels is not only caused by the continuous change in wind turbine noise source levels but also by the unsteady flow field and the ground characteristics between the turbine and receiver. To take these phenomena into account, a consistent numerical technique that models the sound propagation from the source to receiver is developed.

Dual-band pixelless upconversion imaging devices.

We have proposed a type of mid-infrared (MIR) and far-infrared (FIR) dual-band imaging device, which employs the photon frequency upconversion concept in a GaN/AlGaN MIR and FIR dual-band detector integrated with a GaN/AlGaN violet light emitting diode. On the basis of the photoresponse of single-period GaN/AlGaN dual-band detectors, we present the detailed optimization of multiperiod GaN emitter/AlGaN barrier detectors and their applications to dual-band pixelless upconversion imaging. Satisfying images have been received through the analysis of the modulation transfer function and the upconversion efficiency in the GaN/AlGaN dual-band pixelless upconverters, which exhibit good image resolution, high quantum efficiency, and negligible cross talk.

Direct evidence of Kerr-like nonlinearity by femtosecond Z-scan technique.

Kerr-like nonlinearity n(2) (THz) induced via terahertz (THz) radiation and linear electro-optic (EO) effect is investigated in (110), (111) and (100) oriented ZnTe crystals using Z-scan technique with femtosecond laser pulses. We have proposed a model, taking into account the Kerr-like nonlinearity n(2) (THz), to describe well the experimental incident polarization dependence of the nonlinear refractive index n(2). It is found that for a (110) ZnTe crystal the nonlinear refractive index n(2) is dominated by the Kerr-like nonlinearity n(2) (THz), while n(2) in the (111) ZnTe crystal mainly comes from the combined contributions of the Kerr-like nonlinearity n(2) (THz) and conventional Kerr nonlinearity n(2) (Kerr).