Physical optics

About: Physical optics is a research topic. Over the lifetime, 5342 publications have been published within this topic receiving 101388 citations. The topic is also known as: wave optics.

Choosing mesh spacings and mesh dimensions for wave optics simulation

Abstract: One of the most common and important tasks in wave optics simulation is choosing what mesh spacings and mesh dimensions to use for a given problem. To obtain correct results, it is crucial that the mesh spacings are sufficiently small and the mesh dimensions sufficiently large, but if one makes the spacings too small, or the dimensions too large, that can greatly increase the simulation run time, and that may be unaffordable. It is therefore important to understand exactly what the applicable constraints are, so that one may choose mesh spacings and dimensions that will yield correct results without being over-conservative. However this problem can be nontrivial, especially when modeling propagation through aberrating media, or when there is potentially useful a priori information available which might allow us to relax the modeling constraints. For example, if the light source is known to be well-collimated, we know that all of the light to be modeled will be concentrated along one axis, allowing us to use smaller meshes than we would if the light were uncollimated. Similarly, if the receiver has a limited field of view, we need not model any light incident upon it from angles outside its field of view. In this paper we present a simple general method to determine what mesh spacings and dimensions will work for any given wave optics propagation problem, including problems involving propagation through aberrating media and/or a priori information about the source and/or receiver.

Fourier Transform Method for the Treatment of the Problem of the Reflection of Radiation from Irregular Surfaces

Abstract: A method is presented which can be used for the calculation of the distribution of energy reflected from irregular surfaces. The formulation is useful for the first boundary value problem and can be used in either two‐ or three‐dimensional problems with any given incident field. The solution is reduced to quadrature with negligible error when the average square of the slope of the reflecting surface is small and when the wavelength of the incident radiation is not small compared with the displacement of the surface from its average value. A numerical example is worked, the sinusoidal surface, and is compared with experiment and with a method due to Rayleigh. It is found that the Fourier transform method is preferable to previous methods, notably those which can be classified physical optics (such as Rayleigh's), since the error in the transform method is of second order in the surface slope whereas the error in previous methods is of first order in the same quantity.

GTD Terrain Reflection Model Applied to ILS Glide Scope

Abstract: The capability of calculating the reflection of electromagnetic signals from uneven terrain has many applications. One of these is the determination of instrument landing system (ILS) glide slope performance. For this application the wavelength is approximately 1 m, incidence angles are usually near grazing, and the fields are horizontally polarized, so that gross irregularities such as dropoffs and hills are more important than surface roughness. Past approaches used to calculate the ground reflections for this application have been three-dimensional physical optics models which were very cumbersome and time consuming and which neglected important diffraction and shadowing phenomenon; a two-dimensional physical optics model which was faster than the three-dimensional models but ignored many shadowing and transverse terrain variation effects; and a half-plane diffraction model which is applicable only to a specified type of terrain geometry. In this paper a terrain reflection model based on the geometrical theory of diffraction (GTD) is described which can accommodate any piecewise linear terrain profile, requires less computer time than the physical optics models, is capable of including transverse terrain effects, and determines the reflected fields with all important diffraction and blockage effects included.

Phase matrix and cross sections for single scattering by circular cylinders: a comparison of ray optics and wave theory.

Abstract: The phase matrix and several quantities for single scattering by an arbitrarily oriented circular cylinder are formulated by using the approximation of ray optics, which includes geometrical reflection and refraction plus Fraunhofer diffraction; then the effects of polarization are considered. Computations were made using electromagnetic wave theory and ray optics approximations for m = 1.31–0.0i and 1.31–0.1i. Results by these methods approach one another as the ratio of the cylinder's circumference to the incident wavelength increases. One of two ray optics approximations proposed requires less computation time than wave theory. The applicability of the ray optics approximation is dependent on the orientation of the cylinder relative to the incident light as well as the size parameter and, moreover, dependent on what quantity for single scattering is compared.

Characterization of the internal energy density in Mie scattering

Abstract: The distribution of the internal field energy in nonresonant Mie scattering is shown to exhibit certain regularities not previously noticed. The distribution, when suitably expressed, is independent of the size of the spherical scatterer and obtainable from geometric optics, with the average over any spherical surface calculable in closed form. A discontinuity at a radius r = a/n is found and described, where a is the radius of the sphere and n the refractive index.