The combined radiation power of current sources with different polarizations has been investigated through the manipulation of light propagation within zero-index materials. When the permittivity (permeability) of materials becomes zero, the amplitudes of transverse electric (magnetic) fields in media are a function of the position of the current sources. It is found that the amplitudes of electromagnetic fields excited in isotropic double-near-zero (DNZ) materials display a homogenous distribution, which can help to realize a high-quality power combination of the full polarization radiation field. Furthermore, the DNZ photonic crystal (PC) is designed and applied to approach full polarization power combination with multiple sources arranged in a complex pattern. In addition, the radiation field patterns of full polarization power combination could be easily controlled by changing the shape or boundary conditions of the PC.
The scattering effects of random media severely limit the imaging capability of optical detection and ranging systems through clouds, fog, rain, turbid water, dust, biological tissues, and other medias. The method of precisely simulating the process of light transmission to invert object images is gradually becoming the mainstream approach for imaging through random media. The diffusion equation method, which involves solving the point spread function of light diffusion in random media, is a commonly used approach to simulate the transmission of light in random media. However, the diffusion equation method struggles to describe the behavior of light diffusing into objects within random media and returning directly. Based on the diffusion equation method, we have proposed a point spread function to describe the behavior of light diffusing into objects within random media and returning. Through the application of Wiener filtering, successful imaging of objects submerged in random media has been achieved. The imaging method we have proposed may have potential applications in fields such as medicine, search and rescue operations, exploration, and autonomous driving, where objects are typically submerged in random media.
The presence of random scattering layers diffuses incident field information of objects, which interferes with the imaging process of objects, resulting in the geometry of objects not being accurately imaged. In this paper, we propose and experimentally demonstrate an approach for computational imaging of moving hidden objects through random scattering layers based on speckle cross-correlation method. Theoretical analysis denotes that imaging of moving objects is achieved by the speckle cross-correlation function and the conventional Fienup-type iterative phase-retrieval algorithm. The proposed results may have applications in imaging through grove and biological tissues.
The scattering effect of random media such as clouds, turbid water, and biological tissue severely restricts the imaging and ranging capabilities of optical detection and ranging systems through media. The method of using precise simulation of the light transmission process to invert the target image has gradually become the mainstream method for imaging through scattering media. In the diffusion equation method commonly used for simulating light transmission in random media, it is necessary to strictly determine the boundary of the random media, which is difficult to achieve in practical applications. We propose a boundless point spread function for simulating the propagation of light in random media, which equates the diffusion of light in a finite-sized random media to that in an infinitely large random media, without obtain the boundary of the random media. Our proposed imaging method may have potential applications in fields such as medicine, rescue and relief, exploration, and autonomous driving, where obtaining information about the boundary of random media is typically difficult.
We have used Terahertz time-domain spectroscopy(TDS) to investigate the dielectric properties of water and water solutions of containing different ions. The complex permittivity of NaCl solutions, for different concentrations of ions, was obtained by attenuated total reflection(ATR) method. We have observed that, when increasing o ion concentration, the real part and imaginary part of the permittivity are increased. Furthermore, we also calculate the dielectric constant of ionic aqueous solutions with different concentrations based on molecular dynamics method. The simulation method, based on Newton mechanics, can estimate the dielectric constant of liquid substances without the experimental limitation.
Using first-principles calculations, the terahertz dielectric and thermal properties of cubic silicon carbide (3C-SiC) are investigated for a wide range of temperature ranging from 0K to 2500K with the density functional perturbation theory (DFPT) and the quasi-harmonic approximation (QHA).
Spoof surface plasmons (SSP) on the corrugated metal surfaces has attracted intense research interests and can find many interesting applications such as wave guiding, imaging, sensing, etc in microwave and terahertz (THz) band. Previous studies show that the intense near-field of SSP mode on the metallic grating can be used to develop a new enhanced radiation source which is induced by injected electron beam. In this paper, we study SSP mode on a modified metallic grating, i.e. the inverse L-shaped sub-wavelength metallic grooves. The general dispersion relation is obtained with a modal expansion method by solving field expressions in different regions along with proper boundary conditions. The theoretical result is also verified by finite integration method and good agreement is observed. Based on the dispersion result, a terahertz radiation source on the inverse L-shaped metallic grooves is proposed and studied by FDTD simulation. The results reveal that SSP mode can be efficiently excited by injected electron beam when the dispersion is matched well with each other. Also, the output power revolution of SSP mode and electron beam energy change are presented in the structure. The presented studies are instructive to design more efficient THz electronic sources based on the generation of SSP on the corrugated metal surface with gradient groove depth.
We investigate the ISAR imaging in background noises by using the analytical solutions and physical optics within the terahertz region. When increasing the frequency band wide, the scattering signals of the metal sphere are enhanced by the coherent measurement technique, and the background noises are effectively canceled. Furthermore, the resolution of SAR imaging is improved to precisely locate the scattering centers of objects. However, the increased band wide seemly decreases the contrast of imaging due to the discrete grids of filtered back projection algorithm.
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