Yuesong Jiang

Scattering of a focused Laguerre?Gaussian beam by a spheroidal particle

A focused Laguerre–Gaussian beam scattered by a homogeneous prolate spheroidal particle is studied for on-axis incidence. An approach to expanding a focused Laguerre–Gaussian beam in terms of the spheroidal wavefunctions in spheroidal coordinates is presented. By using the localized approximations method, the beam-shape coefficients are evaluated and the results agree with the cases of on-axis incidence. Calculations of the far-field scattering intensity are performed to study the shaped beam scattered by a spheroid, which has different size parameters and eccentricities.

High-Frequency Method for Terahertz Radar Cross Section of Conductive Targets in Free Space

The high-frequency method for the prediction of the terahertz (THz) radar cross section (RCS) of conductive targets with extremely electrically large size in free space was presented. In order to consider the scattering flelds of the perfectly electric conducting (PEC) targets with extremely electrically large size in free space, the Greens function was introduced into the conventional physical optics (PO) method which was combined with the graphical electromagnetic computing (GRECO) method and improved using the partition display algorithm. The shadow regions were eliminated quickly by displaying lists of OpenGL to rebuild the targets, and the geometry information was attained by reading the color and depth of each pixel. The THz RCS of conductive targets can be exactly calculated in free space. The RCS comparison between the partition display GRECO prediction by the self-written Visual C++ 2010 program and the simulation of FEKO software with the large element PO method proves the validity and accuracy of the proposed method. The results provide an important basis and method for the potential applications of THz radar in many flelds such as military, astronomy and remote sensing.

Calculation of the overlap factor for scanning LiDAR based on the tridimensional ray-tracing method

The overlap factor is used to evaluate the LiDAR light collection ability. Ranging LiDAR is mainly determined by the optical configuration. However, scanning LiDAR, equipped with a scanning mechanism to acquire a 3D coordinate points cloud for a specified target, is essential in considering the scanning effect at the same time. Otherwise, scanning LiDAR will reduce the light collection ability and even cannot receive any echo. From this point of view, we propose a scanning LiDAR overlap factor calculation method based on the tridimensional ray-tracing method, which can be applied to scanning LiDAR with any special laser intensity distribution, any type of telescope (reflector, refractor, or mixed), and any shape obstruction (i.e., the reflector of a coaxial optical system). A case study for our LiDAR with a scanning mirror is carried out, and a MATLAB program is written to analyze the laser emission and reception process. Sensitivity analysis is carried out as a function of scanning mirror rotation speed and detector position, and the results guide how to optimize the overlap factor for our LiDAR. The results of this research will have a guiding significance in scanning LiDAR design and assembly.

High-Frequency Method for Scattering from Coated Targets with Extremely Electrically Large Size in Terahertz Band

Abstract This article presents a high-frequency method for the prediction of radar cross-section of coated targets with extremely electrically large size in the terahertz band in free space. To consider the scattering characteristics of the coated targets with a rough surface in the terahertz band, taking into account the effect of surface roughness, the reflection coefficients on the smooth coating surface can be modified; the equivalent electric and magnetic currents on the surface can then be corrected by the modified reflection coefficients to obtain the electric and magnetic induced current densities on the rough coating surface. Therefore the physical optics method, which was combined with the graphical electromagnetic computing method and improved using the partition display algorithm, can be used to solve the scattered fields, and the radar cross-section of the coated targets with a rough surface in the terahertz band can then be obtained. Numerical results for several coated targets, such as the mother warhead of the Minuteman III intercontinental ballistic missile and VFY-218 aircraft, are given and discussed. The results provide an important basis and method for applications of terahertz radar in many fields, such as military, astronomy, and remote sensing, in the future.

Statistical properties of polarization image and despeckling method by multiresolution block-matching 3D filter

The theoretical and experimental investigations on the polarization imagery system of speckle statistical characteristics and speckle removing method are researched. A method to obtain two images encoded by polarization degree with a single measurement process is proposed. A theoretical model for polarization imagery system on Müller matrix is proposed. According to modern charge coupled device (CCD) imaging characteristics, speckles are divided into two kinds, namely small speckle and big speckle. Based on this model, a speckle reduction algorithm based on a dual-tree complex wavelet transform (DTCWT) and blockmatching 3D filter (BM3D) is proposed (DTBM3D). Original laser image data transformed by logarithmic compression is decomposed by DTCWT into approximation and detail subbands. Bilateral filtering is applied to the approximation subbands, and a suited BM3D filter is applied to the detail subbands. The despeckling results show that contrast improvement index and edge preserve index outperform those of traditional methods. The researches have important reference value in research of speckle noise level and removing speckle noise.

Laser speckle reduction based on compressive sensing and edge detection

Polarization active imager technology obtains images encoded by parameters different than just the reflectivity and therefore provides new information on the image. So polarization active imager systems represent a very powerful observation tool. However, automatic interpretation of the information contained in the reflected intensity of the polarization active image data is extremely difficult because of the speckle phenomenon. An approach for speckle reduction of polarization active image based on the concepts of compressive sensing (CS) theory and edge detection. First, A Canny operator is first utilized to detect and remove edges from the polarization active image. Then, a dictionary learning algorithm which is applied to sparse image representation. The dictionary learning problem is expressed as a box-constrained quadratic program and a fast projected gradient method is introduced to solve it. The Gradient Projection for Square Reconstruction (GPSR) algorithm for solving bound constrained quadratic programming to reduce the speckle noise in the polarization active images. The block-matching 3-D (BM3D) algorithm is used to reduce speckle nosie, it works in two steps: The first one uses hard thresholding to build a relatively clean image for estimating statistics, while the second one performs the actual denoising through empirical Wiener filtering in the transform domain. Finally, the removed edges are added to the reconstructed image. Experimental results show that the visual quality and evaluation indexes outperform the other methods with no edge preservation. The proposed algorithm effectively realizes both despeckling and edge preservation and reaches the state-of-the-art performance.

Properties of single wall carbon nanotubes array antennas in the optical regime

Single wall carbon nanotubes (SWCNTs) can be metallic, depending on their chirality. For their nanoscale geometric dimension, SWCNTs can be used as antennas to convert high-frequency electromagnetic radiation such as optical radiation into localized energy and vice versa. However, at optical frequencies, traditional antenna design theory fails for metals behave as strongly coupled plasmas. As a matter of fact, an optical antenna responds to a shorter effective wavelength which depends on the material properties and geometric parameters. In this letter, we derived the relationship of effective wavelength with the wavelength of incident radiation for SWCNTs optical antenna, assuming that the SWCNTs can be described by a free electron gas according to the Drude model. SWCNTs optical antenna holds great promise for increasing solar energy conversion efficiency.

Scattered light: improving photoacoustic spectral measurement with a drug tablet

Photoacoustic spectroscopy (PAS) is a powerful tool for the study of the absorption spectra of solid samples. Scattered light, which used to be a main error source in conventional absorption spectroscopy, is not a problem for PAS, and furthermore, in this paper it is helpful for photoacoustic spectroscopy measurement. In this work, the photoacoustic spectra of an olanzapine tablet and its powder have been investigated. Differential analysis was used to eliminate the background signal generated by the photoacoustic cell. It is found that the photoacoustic spectrum of olanzapine in the powdered olanzapine tablet has the same spectral features as that of the pure olanzapine powder, while the photoacoustic spectrum of the olanzapine tablet does not have, although the ingredients in both are completely the same. This phenomenon can be interpreted as the light scattering effects in the powdered olanzapine tablet. The light scattering effects in a solid mixture amplify the photoacoustic spectral features of the main light-absorbing ingredient in the mixture, rather than enhance the measured photoacoustic signal over the whole measured wavelength range, which is different from the influence of light scattering effects on a single-ingredient solid powder. Based on this work, a method is proposed to preliminarily fast identify the light-absorbing ingredient in a solid mixture. Using the method, a drug tablet can be measured directly in solid state and hardly need sample preprocessing, and thus the time for composition analyses will be reduced significantly.

Optical aperture synthesis imaging with fractional Fourier-domain filtering

The fractional Fourier transform, which is a generalization of the classical Fourier transform, is introduced into an optical aperture synthesis (OAS) system by which imaging of an astronomical object can be achieved. We introduce fractional Fourier optical imaging and fractional Fourier-domain filtering (FFDF), and then present the schematic diagram of an OAS imaging system with FFDF. The modulation transfer function of an OAS system with FFDF is compared with that of an OAS system in the same condition. The result indicates that the OAS system with FFDF has larger practical cutoff frequency when the fill factor is smaller. Furthermore, the quality of imaging and restoration also demonstrates this conclusion.

High-frequency analysis on RCS from terahertz conductive targets in free space

The high-frequency method for solving the Radar Cross Section (RCS) of Terahertz conductive targets in free space is presented in this paper. Consider the environment of free space, the free space physical optics integral equation is deduced by introducing the free space Green’s function into the Physical Optics (PO) method. Combined with the GRaphical-Electromagnetic COmputing (GRECO) method, the shadow regions are eliminated quickly and the geometry information is attained by reading the color and depths of each pixel. The RCS of Terahertz conductive targets can be exactly calculated in free space. The numerical results show that this method is efficient and accurate.