Principles Of Physical Optics Research Articles

Fundamentals of Determination of the Biological Tissue Refractive Index by Ellipsoidal Reflector Method

This paper presents the theoretical fundamentals, prerequisites for creation, and peculiarities of modeling a new method for determining the refractive index of biological tissues. The method uses a mirror ellipsoid of revolution as an optical element to ensure total internal reflection phenomena. This paper thoroughly analyzes the differences in the refractive index of healthy and pathological tissues on a biometric diagnostic basis. The analysis is used to model the measurement setup’s parameters. This paper also considers various methods of determining the refractive index of biological tissues based on different principles of physical optics, such as interferometry, refractometry, ellipsometry, and goniophotometry. It systematizes typical optical elements of total internal reflection that can be used in goniophotometry. It justifies the selection of the element base for the goniometric installation based on the ellipsoidal reflector method. A simulation of the installation operation was carried out for various parameters of the ellipsoidal reflector, ensuring the measurement of the biological tissue refractive index from 1.33 to 1.7. This paper also proposes a constructive solution for manufacturing an ellipsoidal reflector of the required configuration.

Research on the efficient EM modeling method from multilayered anisotropic medium-metal composite targets

The paper presents a high-frequency modeling approach tailored for the electromagnetic (EM) scattering characteristics from electrically large radar targets coated with multi-layered anisotropic mediums (MLAMs). The approach begins by deriving the plane-wave spectrum expression for the incident EM field within MLAMs. It then employs spectral domain full-wave analysis method (SDFWAM) to obtain an analytical representation of the scattering field, further leveraging saddle point evaluation (SPE) to derive asymptotic solutions in the spatial domain. By integrating principles of physical optics (PO) and the tangent plane approximation, the far-field scattering characteristics of target enveloped in the specified medium are efficiently delineated. Validations against standard structure and the Misty satellite model reveal the method's pronounced alignment with the method of moments – finite element method (MoM-FEM) hybrid numerical algorithm, underscoring its notable computational efficiency. Furthermore, in conjunction with scattering sources decomposition technique, the approach is applied to optimize the radar cross-section (RCS) of the Su-57 aircraft, achieving precise and intelligent RCS control at minimal material cost. In conclusion, this research offers pivotal technological and theoretical foundations for EM scattering prediction, stealth design, and performance assessment in radar target domains.

Microwave hologram reconstruction for cylindrical geometry

Microwave imaging is a technique for evaluation of hidden or embedded objects in an optically opaque structure (or media) using electromagnetic waves in microwave regime. The result of the study is a microwave image of the internal structure of the investigated object, which is built by reconstructing the electromagnetic field scattered by the object (microwave hologram), recorded using some radar system at some aperture. Along with the widespread flat aperture, a cylindrical aperture is often used in personnel screening systems, microwave system for automated body measurement for apparel fitting, and medical tomographic scanners. Cylindrical geometry requires special holograms reconstruction methods. The work is dedicated to comparison of three hologram reconstruction methods: №1 – back projection, №2 – back propagation and №3 – Gauss–Newton, and identifying the advantages and disadvantages of each method. All methods were adopted to cylindrical geometry, software implemented using Python programming language and compared. Comparison was performed by reconstruction of microwave holograms of the same objects. Microwave holograms for comparison were calculated in accordance with the principles of physical optics for point scatterers and using the computational electromagnetics software product FEKO for solid objects. Comparison criteria were: speed of calculations, quality of obtained microwave images, required random access memory (RAM) of the computer. Based on the results of numerical experiments, the following conclusions can be made. For both point and solid objects, all methods have showed a similar quality of the obtained microwave images, the difference turned out to be minimal both in visual and numerical estimation. The advantage of method №1 is the simplicity of its software implementation. In addition, using the first method, you can easily do reconstruction for any area (line, surface, volume), the position of which can be arbitrary in relation to the positions of the samples of the radar signal. Method №2 is the fastest method. With the parameters considered in the article, it is two orders of magnitude faster than method №1, and its performance can be easily increased by parallelizing calculations for different radii. Among the shortcomings, one can note the complexity of its software implementation and the dependence of the position and size of the reconstructed area on the location and number of samples of the radar signal. A significant drawback of method №3 is its high requirements to the RAM of the computer, as well as low speed of calculations. When processing microwave holograms with a large number of samples, calculations may require more memory than is installed in the computer, and the calculation time will increase many times due to the continuous exchange of data with the hard disk, or it will be impossible to do the calculations at all.

Channel Estimation of MIMO-OFDM through Wavelet Transform to Improve the Spectral Efficiency and Data Transmission Rate

We define a new wavelet transform that is based on a recently defined family of scaling functions: the fractional B-splines. The interest of this family is that they interpolate between the integer degrees of polynomial B- splines and that they allow a fractional order of approximation. The approximation can determine noise in communication signals and help in signal reconstruction and channel estimation in MIMO receiver system. In free space optical communication links, the turbulent atmospheric channel causes fluctuations in both intensity and phase of the transmitted optical signal which degrades their performance. In order to make free space optical communications commercially viable, there is a need for characterizing the atmospheric effects on the received signal statistics, and possibly correcting for the signal degradation using physical optics principles and advanced real-time signal processing techniques. As part of this work, we have constructed an experimental free space optical link over 100 meters so as to characterize the effects of inner-scale and outer-scale turbulence effects, and used it as the platform for carrying out the above objectives. Through these techniques, we have demonstrated bit error rate (BER) reduction and propose to estimate channel accurately.

Spectral discrimination in color blind animals via chromatic aberration and pupil shape.

We present a mechanism by which organisms with only a single photoreceptor, which have a monochromatic view of the world, can achieve color discrimination. An off-axis pupil and the principle of chromatic aberration (where different wavelengths come to focus at different distances behind a lens) can combine to provide "color-blind" animals with a way to distinguish colors. As a specific example, we constructed a computer model of the visual system of cephalopods (octopus, squid, and cuttlefish) that have a single unfiltered photoreceptor type. We compute a quantitative image quality budget for this visual system and show how chromatic blurring dominates the visual acuity in these animals in shallow water. We quantitatively show, through numerical simulations, how chromatic aberration can be exploited to obtain spectral information, especially through nonaxial pupils that are characteristic of coleoid cephalopods. We have also assessed the inherent ambiguity between range and color that is a consequence of the chromatic variation of best focus with wavelength. This proposed mechanism is consistent with the extensive suite of visual/behavioral and physiological data that has been obtained from cephalopod studies and offers a possible solution to the apparent paradox of vivid chromatic behaviors in color blind animals. Moreover, this proposed mechanism has potential applicability in organisms with limited photoreceptor complements, such as spiders and dolphins.

Principles of Physical Optics: C.A. Bennett

Principles of Physical Optics: C.A. Bennett

Characterization of atmospheric turbulence effects and their mitigation using wavelet-based signal processing

In free space optical communication links, the turbulent atmospheric channel causes fluctuations in both intensity and phase of the transmitted optical signal which degrades their performance. In order to make free space optical communications commercially viable, there is a need for characterizing the atmospheric effects on the received signal statistics, and possibly correcting for the signal degradation using physical optics principles and advanced real-time signal processing techniques. As part of this work, we have constructed an experimental free space optical link over 100 meters so as to characterize the effects of inner-scale and outer-scale turbulence effects, and used it as the platform for carrying out the above objectives. A key aspect of our work is the experimental determination of the individual contribution of scintillations and beam wandering to the received signal variance. We have proceeded to correlate such effects with atmospheric parameters with the aim of building a model through which the channel properties may be estimated based on a measurement of the atmospheric parameters. Such analysis has been carried out over a 24 hour period to include a full day-night cycle and also to consider the effect of temperature. In this paper, we have also investigated methods of reducing the atmospheric effects such as scintillations and beam wandering. Specifically, we have demonstrated reduced scintillation-related variance by aperture averaging technique, and reduced beam wandering-related variance using wavelet based signal processing. Through these techniques, we have demonstrated bit error rate (BER) reduction by a factor of 138 compared to the original signal for our experimental free space optical link.

Improvement on the Forward-backward Iterative Physical Optics Algorithm Applied to Computing the RCS of Large Open-ended Cavities

The equivalent impedance boundary condition and the transmission line theory are used to analyze the surface impedance and reflective coefficient of the PEC surface coated with a thin absorber layer. Then, the IPO iterative equation is deduced by combining the surface impedance and reflective coefficient with the asymptotic principles of physical optics. The method of initial value succession is introduced to the forward-backward iterative physical optics (FBIPO) algorithm. The initial residual error is reduced by inheriting the current values. Combined with a relaxation parameter, the method improves the convergence of the FBIPO algorithm for cavity scattering problems. The accuracy of RCS calculation is also enhanced by using a more precise mixed-face model. The RCS of a jet inlet model is calculated, with its results in good agreement with the experimental ones. The method is also used to calculate the RCS reduction of a circular wave guide by coating the inner wall with absorber material.

Ray Tracing With PO/PTD for RCS Modeling of Large Complex Objects

The present paper deals with a new efficient approach in order to assess the simulation of scattered fields from arbitrary metallic objects. The basic idea is to combine a ray tracing algorithm with the principles of physical optics (PO) and the physical theory of diffraction (PTD). The ray tracing algorithm stochastically launches discrete rays and uses a ray density normalization. In order to perform simulations at finite objects the PO/PTD formulation is required. Thus, fast intersection routines can be implemented, while the ray density formulation reduces the PO and PTD integrals to a pure sum of ray contributions. Simulation results obtained with this model are verified by comparison with both exact simulations using a method of moments (MoM) code and measurement results, proving an excellent accuracy and fast computation even at complex objects. With this asymptotic approach, scattering properties of large objects that are too complex for exact methods can be analyzed with rather moderate computation efforts. Typical applications include the simulation of low observability (LO) designs as well as the generation of databases for identifying unknown aircraft by their radar signature.

Iterative solutions of MFIE for computing electromagnetic scattering of large open-ended cavities

The analysis of high-frequency scattering from electrically large open cavities is addressed in the paper. A magnetic-field integral equation (MFIE) for the equivalent currents on the interior cavity walls is obtained and solved by two different algorithms based on high-frequency principles of physical optics (PO). Once the currents are known, the scattered fields are obtained by using aperture integration (AI) in the cavity mouth, or a reciprocity integral (RI) over a surface close to the termination. Numerical results are presented which demonstrate the convergence and accuracy of the proposed methods, by comparison with modal reference solution.

Comparison of reflectometer fluctuation measurements from experiment and two-dimensional numerical simulation

A comparison is made between the statistical properties of phase and power signals from a homodyne reflectometer on the STOR-M tokamak and simulated signals from a two-dimensional distorted surface model. Experimental results from edge density fluctuations show phase fluctuations of less than half a fringe with a Gaussian distribution and no phase ramping. Reflected power fluctuations are substantial (up to 45%) and are non-Gaussian distributed. Both phase and power signals display broadband turbulent frequency spectra with spectral indexes of −3.5. Fluctuations in the scattered electric field are calculated in the model using physical optics principles with a Gaussian reflectometer incident beam profile and structured surface distortions to replicate variations in the plasma cutoff layer. Simulation results display a wide range of features depending on three parameters, surface fluctuation amplitude, transverse wavenumber spectrum, and incident beam width. With the beam width fixed by the experiment (50 mm) and (realistic) fitted values of 1–2 mm for the root mean square fluctuation depth and 2 cm−1 for the k-spectral width—good agreement is found with the experiment.

An iterative physical optics approach for analyzing the electromagnetic scattering by large open-ended cavities

A formulation based on the high frequency asymptotic principles of physical optics is developed for analyzing the scattering by relatively arbitrary open-ended waveguide cavities containing complex interior terminations. A magnetic field integral equation (MFIE) is obtained for the equivalent currents on the interior cavity walls and is solved using an iterative physical optics (IPO) algorithm which iteratively applies physical optics to account for multiple reflections inside the cavity. The number of iterations required for convergence is related to the expected number of important reflections. The IPO method is more approximate than a matrix solution of the MFIE, but it is quite accurate for electrically large cavities and is much more efficient. Numerical results are presented which demonstrate the convergence and accuracy of the method by comparison with modal reference solutions.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The value of a study of wave motion on the learning of certain principles of physical optics

The value of a study of wave motion on the learning of certain principles of physical optics

Motion of charged particles in a helically perturbed magnetic field

The motion of a charged particle in a magnetic field composed of a uniform axial component and a spatially rotating transverse component is analysed. Solutions of the nonlinear equations of motion are obtained which describe an oscillatory transfer of kinetic energy between axial motion and rotational motion in the transverse plane. A simple physical description of the interaction in terms of impulsive Lorentz forces is given which has formal similarity to the Huygens' principle in physical optics.

The application of the principles of physical optics to crystal-structure determination

The analogy between the diffraction of light by a set of holes, and the diffraction of X -rays by a set of atoms can be exploited in solving many different types of X -ray diffraction problem . A special instrument has been built to obtain diffraction patterns rapidly, making possible several different approaches to the determination of crystal structures. Of particular importance is that involving the ‘optical transform’ of a molecular representation. Consideration of the optical transform, which is closely related to the Fourier transform, can, for simple space groups, lead directly to the crystal structure. For more complicated space groups, optical transforms of molecules in different orientations have to be combined, and some rules governing their combination are given. The discussion includes several examples of structures which have been determined by optical-transform methods. These methods require the presentation of the X -ray data in the form of a weighted reciprocal lattice, from which information can often be obtained directly. For several new structures such information as the separation of two similarly oriented molecules, or the orientation of hexagonal arrangements of atoms, has been deduced by considering the weighted reciprocal lattice alone. In some cases this led to the complete structure; in others it was a valuable supplement to the optical transform method. Despite the lack of quantitative accuracy, optical methods can be of use in refining approximate structures by ordinary Fourier methods. Examples are given of the deter­mination of the relative phase angles of the reflexions of both centrosymmetric and non-centrosymmetric structures. The relationships between optical methods and more conventional methods of structure determination are discussed.

Blue Sun and Moon

Paul and Jones1, discussing the blue sun caused by selective absorption of a cloud of uniform spheres of radius r in light of wave-length λ, have considered the curve relating K (the ratio of effective to geometrical cross-section of a particle) and α, where α= 2πr/λ. They suggest a simple physical explanation of the maxima and minima of this curve on the basis of resonances. The maxima and minima, in the case of small dielectric spheres can also be explained from the principles of physical optics; this point of view was used by Van de Hulst2 in considering some aspects of the subject that could not so readily be treated by electromagnetic theory.

Optical methods in crystal-structure determination.

DURING the war years, Sir Lawrence Bragg put forward several interesting suggestions for the application of the principles of physical optics to crystal-structure determination1,2. These methods seem to us to be of particular importance at the present time in order both to ease the burden of calculation which has enveloped the subject and also to introduce new experimental methods of tackling the initial stages of a structure investigation.

(1) The Principles of Physical Optics: an Historical and Philosophical Treatment (2) Handbuch der biologischen Arbeitsmethoden

(1) ACERTAIN philosopher once said, “Learn the past, so that you may know the future”; but history appeals very differently to different minds; one sees in it a subject satisfying in itself, while to another the past is dead save in so far as it yields lessons for present and coming days. Prof. Ernst Mach's “Principles of Physical Opticsae is bound to make a wide appeal to the many who cannot find much time to go back to the original authors of optical theory and practice, though it must be noted that the matters treated do not extend to the more contentious topics of the present day, such as the nature of light, the problem of the ether, the quantum theory, and so on; they are confined to those older parts of the subject which are adequately treated on the basis of the undulatory theory of light. (1) The Principles of Physical Optics: an Historical and Philosophical Treatment. By Ernst Mach. Translated by Dr. John S. Anderson and Dr. A. F. A. Young. Pp. xi + 324 + 10 plates. (London: Methuen and Co., Ltd., 1926.) 21s. net. (2) Handbuch der biologischen Arbeitsmethoden. Herausgegeben von Prof. Dr. Emil Abderhalden. Lieferung 187. Abt. 2: Physikalische Methoden, Teil 2, Heft 1. Das Interferometer, seine Anwendung zur Untersuchung von Gasen und Flussigkeiten, von Paul Hirsch; Ultramikroskopie, von Marie Anna Schirmann; Refraktometrie, von Heinrich Kessler. Pp. 737–906. (Berlin und Wien: Urban und Schwarzenberg, 1926.) 7.50 gold marks.

II. Reply to Mr. Tovey's remarks on a paper on the application of Huyghens's principle in physical optics, inserted in the Lond. Edinb. &amp; Dublin Phil. Mag. for October last; vol. xvii. p. 243

II. <i>Reply to</i> Mr. Tovey's <i>remarks on a paper on the application of</i> Huyghens's <i>principle in physical optics, inserted in the Lond. Edinb. &amp; Dublin Phil. Mag. for October last</i>; vol. xvii. p. 243

LXII. On Mr. Potter's application of Huyghens's principle in physical optics

"LXII. On Mr. Potter's application of Huyghens's principle in physical optics ." The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science, 17(112), pp. 431–432