Near and far field

About: Near and far field is a research topic. Over the lifetime, 15922 publications have been published within this topic receiving 220571 citations.

Magnetic field strength of active region filaments

Abstract: Aims. We study the vector magnetic field of a filament observed over a compact active region neutral line.Methods. Spectropolarimetric data acquired with TIP-II (VTT, Tenerife, Spain) of the 10 830 A spectral region provide full Stokes vectors that were analyzed using three different methods: magnetograph analysis, Milne-Eddington inversions, and PCA-based atomic polarization inversions.Results. The inferred magnetic field strengths in the filament are around 600–700 G by all these three methods. Longitudinal fields are found in the range of 100–200 G whereas the transverse components become dominant, with fields as high as 500–600 G. We find strong transverse fields near the neutral line also at photospheric levels.Conclusions. Our analysis indicates that strong (higher than 500 G, but below kG) transverse magnetic fields are present in active region filaments. This corresponds to the highest field strengths reliably measured in these structures. The profiles of the helium 10 830 A lines observed in this active region filament are dominated by the Zeeman effect.

High-power 808 nm lasers with a super-large optical cavity

Abstract: We present a detailed design and experimental study of diode laser structures emitting at 808 nm based on the combination of a GaAsP quantum well with well-established AlGaAs waveguide structures By increasing the thickness of the confinement layers of the laser structure, its vertical far field divergence is reduced down to 15° with only a small increase of the threshold current and small loss of efficiency 200 µm aperture 'broad area' devices achieve at a heat sink temperature of 25 °C a continuous wave (CW) output power of more than 15 W with a wall-plug efficiency of 50% with a vertical far field divergence of 18° This output power illustrates the excellent high-power performance by using super-large optical-cavity structures with improved beam characteristics in comparison to the conventional broad waveguide lasers

Bandwidth Enhancement of 2-D Leaky-Wave Antennas With Double-Layer Periodic Surfaces

Abstract: Broadband high-gain 2-D Fabry-Perot (FP) leaky-wave antennas (LWAs) consisting of two periodic metallodielectric arrays over a ground plane are presented. Full-wave method of moments (MoM) is employed for the estimation of the near fields upon plane wave illumination and the extraction of the far field directivity and radiation patterns of the LWA. This yields a fast and rigorous tool for the characterization of this type of antennas. Qualitative design guidelines to tailor the antenna directivity bandwidth are provided for the first time based on a detailed analysis of the excited modes. Numerical examples are given to demonstrate the technique and prove the improvement in the antenna bandwidth. The proposed antenna exhibits a six-fold bandwidth improvement compared with the single array LWA with the same directivity. Simulated and experimental results from a finite size antenna prototype are presented.

Characterization of the Open-Ended Coaxial Probe Used for Near-Field Measurements in EMC Applications

Abstract: A completely automatically near-field mapping system is developed within IRSEEM (Research Institute for Electronic Embedded Systems) in order to determine electromagnetic field radiated by electronic systems. This test bench uses a 3D positioning system of the probe to make accurate measurements. The main element of this measurement tool is the probe. This paper presents a characterization of the open-ended coaxial probe which is used to measure the normal component of the electric field.

Terahertz pulse propagation in the near field and the far field.

Abstract: We present a detailed investigation of the propagation properties of beams of ultrashort terahertz (THz) pulses emitted from large-aperture (LA) antennas. The large area of the emitter is demonstrated to have substantial influence on the temporal pulse profile in both the near field and the far field. We perform a numerical analysis based on scalar and vectorial broadband diffraction theory and are able to distinguish between near-field and far-field contributions to the total THz signal. We find that the THz beam from a LA antenna propagates like a Gaussian beam and that the temporal profile of the THz pulse, measured in the near field, contains information about the temporal and spatial field distribution on the emitter surface, which is intrinsically connected to the carrier dynamics of the antenna substrate. As a result of pulse reshaping, focusing of the THz beam leads to a reduced relative pulse momentum, with implications in THz field-ionization experiments.