Near-Field Vortex Beams Diffraction on Surface Micro-Defects and Diffractive Axicons for Polarization State Recognition

The diffraction of vortex Gaussian laser beams by elementary objects of micro-optics (surface micro-defects) to recognize the type of polarization (linear, circular, radial, azimuthal) of the input radiation was investigated in this paper. We considered two main types of defects (protrusion and depression in the form of a circle and a square) with different sizes (the radius and height were varied). Light propagation (3D) through the proposed micro-defects was modeled using the finite difference time domain (FDTD) method. The possibility of recognizing (including size change) of surface micro-defects (protrusions and depressions) and all the above types of polarization are shown. Thus, micro-defects act as sensors for the polarization state of the illuminating beam. The focusing properties of micro-defects are compared with diffractive axicons with different numerical apertures (NAs). The possibility of sub-wavelength focusing with element height change is demonstrated. In particular, it is numerically shown that a silicon cylinder (protrusion) forms a light spot with a minimum size of the all intensity FWHM of 0.28λ.

Controlling of light with electromagnons

Magnetoelectric coupling in multiferroic materials opens new routes to control the propagation of light. The new effects arise due to dynamic magnetoelectric susceptibility that cross-couples the electric and magnetic fields of light and modifies the solutions of Maxwell equations in media. In this paper, two major effects will be considered in detail: optical activity and asymmetric propagation. In case of optical activity the polarization plane of the input radiation rotates by an angle proportional to the magnetoelectric susceptibility. The asymmetric propagation is a counter-intuitive phenomenon and it represents different transmission coefficients for forward and backward directions. Both effects are especially strong close to resonance frequencies of electromagnons, i. e. excitations in multiferroic materials that reveal simultaneous electric and magnetic character.

Deriving Cloud Velocity From an Array of Solar Radiation Measurements

Spatio-temporal variability of solar radiation is the main variable affecting the photovoltaic power feed-in to the grid. Clouds are the main source of such variability and their velocity is a principal input to most short-term forecast models. The main goal in this study is to estimate cloud speed using radio-metric data using measurements from 8 sensors located at the UC San Diego Solar Energy test bed. Two different methods were developed to estimate the cloud speed based on the correlation between the signals from different sensors. Our analysis showed good agreement between both methods. Additional measurements from nearby METAR and radiosonde stations also show comparable results. Both methods require high variability in the input radiation.

Validation of Solar Radiation Surfaces from MODIS and Reanalysis Data over Topographically Complex Terrain

The magnitude and distribution of incoming shortwave solar radiation (SW↓) has significant influence on the productive capacity of forest vegetation. Models that estimate forest productivity require accurate and spatially explicit radiation surfaces that resolve both long- and short-term temporal climatic patterns and that account for topographic variability of the land surface. This paper presents a validation of monthly average total (SW↓t) and diffuse ( SW↓df ) incoming solar radiation surfaces taken from North American Regional Reanalysis (NARR) data and Moderate Resolution Imaging Spectroradiometer (MODIS) satellite imagery for a mountainous region of the Pacific northwestern United States and Canada. A topographic solar radiation model based on a regionally defined clearness index was used to downscale the 32-km NARR SW↓t surfaces to 1 km, resulting in surfaces that better matched the spatial resolution of MODIS, as well as accounted for elevation and terrain effects including shadowing. Validation was carried out using a series of ground station measurements (n = 304) collected in 2003. The results indicated that annually, the NARR and MODIS SW↓t surfaces were both in strong agreement with ground measurements (r = 0.98 and 0.97), although the strength and bias of the relationships varied considerably by month. Correlations were highest in winter, early summer, and fall and lowest in spring. The NARR and MODIS SW↓df surfaces displayed poorer agreement with ground measurements (r = 0.89 and 0.79), the result of some months having negative correlations. The correlation and spatial structure between NARR and MODIS SW↓t surfaces was enhanced by topographic correction, resulting in more consistent input radiation surfaces for use in broad-scale forest productivity modeling.

The rQ3 branch of HSSD at 656 GHz: Example of a frequency-tripled backward wave oscillator

The rQ3 branch of HSSD with its band head located in the submillimetre-wave region at about 656.5 GHz has been measured up to J = 28 for the ground and for the first excited stretching state. Commencing with medium J quantum numbers (J > 11) the inertial asymmetry splitting is observed, whereas for J > 27 each K-split line separates further into equally strong b- and c-type transitions. For the first time it has been possible to assign Q-branch rotational lines of HSSD to an excited vibrational state, the first excited stretching state νs = 1, which yield differences in the rotational constants: (i) A – B = 93 731.204 (71) MHz and (ii) B – C = 149.69 (14) MHz. The rotational spectra have been recorded with a newly designed wave-guide multiplier, optimized for providing local oscillator power at 660 GHz for astrophysical applications when pumped at 220 GHz. The input radiation was provided by a carcinotron (backward wave oscillator).

Optical Performance of Conical Windows for Concentrated Solar Radiation

Radiative energy transfer through a truncated cone window with a back-plane reflector is considered. This geometry is proposed for a high-pressure direct-radiation (volumetric) central solar receiver for use in combined-cycle electricity generation. The transmission and loss characteristics, computed by ray-tracing, are parameterized by the angle of incident radiation relative to the cone axis. The overall performance of the window is an integral of the angle-dependent transmission data, weighted by the actual distribution of input radiation, over all incidence angles. This parameterization provides insight and assists in tailoring of the window geometry to different solar collection methods. Results are presented for several window geometries. Overall window performance is presented for a dish-type distribution of input radiation.