Showing papers on "Angular aperture published in 2020"

Wide-Angle Polarization-Independent Paratellurite-Based Acousto-Optic Laser Radiation Modulator

Abstract: High-efficiency wide-angle polarization-independent acousto-optic diffraction of laser radiation in a paratellurite-based modulator is experimentally studied. The previously published main theoretical principles are confirmed. We have shown that the angular aperture of the acousto-optic modulator can be ~8° in an ultrasonic frequency range of 135–68 MHz depending on the light wavelength and 2°–5° in the range of 20–30 MHz. A wide-angle acousto-optic depolarized laser radiation modulator has been created that operates at a wavelength λ = 1.06 μm with one output depolarized beam and an efficiency of no less than 90% for input radiation with an angular aperture of 30 mrad.

High contrast and resolution 3-D ultrasonography with a clinical linear transducer array scanned in a rotate-translate geometry

Abstract: We propose a novel solution for volumetric ultrasound imaging using single-side access 3-D synthetic-aperture scanning of a clinical linear array. This solution is based on an advanced scanning geometry and a software-based ultrasound platform. The rotate-translate scanning scheme increases the elevation angular aperture by pivoting the array [-45{\textdegree} to 45{\textdegree}] around its array axis (axis along the row of its elements) and then, scans the imaged object for each pivoted angle by translating the array perpendicularly to the rotation axis. A theoretical basis is presented so that the angular and translational scan sampling periods can be best adjusted for any linear transducer array. We experimentally implemented scanning with a 5-MHz array. In vitro characterization was performed with phantoms designed to test resolution and contrast. Spatial resolution assessed based on the full-width half-maximum of images from isolated microspheres was increased by a factor 3 along the translational direction from a simple translation scan of the array. Moreover, the resolution is uniform over a cross-sectional area of 4.5 cm 2. Angular sampling periods were optimized and tapered to decrease the scan duration while maintaining image contrast (contrast at the center of a 5 mm cyst on the order of-26 dB for 4{\textdegree} angular period and a scan duration of 10 s for a 9cm 3 volume). We demonstrate that superior 3-D US imaging can be obtained with a clinical array using our scanning strategy. This technique offers a promising and flexible alternative to development of costly matrix arrays toward the development of sensitive volumetric ultrasonography.

Radio Vortex Communication System Using Partial Angular Aperture Receiving Scheme Under Atmospheric Turbulence

Abstract: For transmission based on long-distance vortex waves, the partial receiving scheme which uses a limited angular aperture receiving and demultiplexing multi-beam can solve the difficulty of the conventional whole beam receiving scheme due to the divergence of the vortex beam. But the atmospheric turbulence is rarely considered in analyzing the stability of the radio vortex (RV) communication system based on the partial angular aperture receiving (PAAR) scheme. Here we first introduce atmospheric turbulence into the RV communication system based on the PAAR scheme. Moreover, in order to compare the effects of turbulence on the PAAR scheme and the whole angular aperture receiving (WAAR) scheme, a new turbulence attenuation degree D model is proposed, which represents the stability of the RV communication system in the atmospheric turbulence environment. Simulation results indicate that the difference of D values between PAAR scheme and WAAR scheme does not exceed the order of 0.01 when the range of refractive index structure constant $C_{n}^{2}$ is ${10^{-17}}{m^{-\\frac {2}{3}}}-{10^{-12}}{m^{-\\frac {2}{3}}}$ and the distance is 90m-120m. When the range of $C_{n}^{2}$ is ${10^{-13}}{m^{-\\frac {2}{3}}}-{10^{-12}}{m^{-\\frac {2}{3}}}$ and the distance is 90m-120m, D value of PAAR scheme is always smaller than that of WAAR scheme. These demonstrations suggest that the RV communication system using PAAR scheme is more stable than that using WAAR scheme in the strong atmospheric turbulence environment.

Adaptive Integration Time in Automotive SAR

Abstract: In this paper, we propose an adaptive sub-aperture integration approach for wide-angle synthetic aperture radar (SAR) with emphasis on the automotive applications. Traditional SAR integration approaches use fixed-width sub-apertures. These approaches suffer from the fact that scatterers may have different persistence widths over the angular aperture and can result in spreading the response across multiple sub-apertures or, conversely, coherently integrate extra noise with the signal. Our proposed method employs change-point detection to identify the persistence widths of the scatterers and consequently increases the coherent integration gain. Experimental results on two datasets validate our proposed methodology.

Luminous module comprising a matrix array of light sources and a bifocal optical system

Abstract: A luminous motor-vehicle module, comprising an array of light sources and a bifocal imaging device that is designed to project an image of each light source, wherein the luminous module comprises at least one primary optical element, which at its exit does not modify in a vertical direction V the angle of the incident rays, and which allows secondary sources to be formed the lateral dimension of which is larger than a lateral dimension of the light sources and the angular aperture of the emitted secondary light beams of which is smaller than an angular aperture of the light beams emitted by the light sources.

Light module comprising an array of light sources and a bifocal optical system

Abstract: A luminous motor-vehicle module, comprising an array of light sources and a bifocal imaging device that is designed to project an image of each light source, wherein the luminous module comprises at least one primary optical element, which at its exit does not modify in a vertical direction V the angle of the incident rays, and which allows secondary sources to be formed the lateral dimension of which is larger than a lateral dimension of the light sources and the angular aperture of the emitted secondary light beams of which is smaller than an angular aperture of the light beams emitted by the light sources.

Theoretical study of quantum-correlated optical-terahertz biphotons

Abstract: We study the statistical properties of optical-terahertz biphotons generated by means of spontaneous parametric down conversion. Numerical dependence of the second-order correlation function is obtained depending on polar angular aperture.