James A. Lockhttps://works.bepress.com/james_lock/Recent works by James A. Locken-usCopyright (c) 2019 All rights reserved.Sat, 01 Oct 2011 07:00:00 +00003600Glitter and Glints on Waterhttps://works.bepress.com/james_lock/74/We present new observations of glitter and glints using short and long time exposure photographs and high frame rate videos. Using the sun and moon as light sources to illuminate the ocean and laboratory water basins, we found that (1) most glitter takes place on capillary waves rather than on gravity waves, (2) certain aspects of glitter morphology depend on the presence or absence of thin clouds between the light source and the water, and (3) bent glitter paths are caused by asymmetric wave slope distributions We present computer simulations that are able to reproduce the observations and make predictions about the brightness, polarization, and morphology of glitter and glints. We demonstrate that the optical catastrophe represented by creation and annihilation of a glint can be understood using both ray optics and diffraction theory. (C) 2011 Optical Society of AmericaDavid K. Lynch et al.Sat, 01 Oct 2011 07:00:00 +0000https://works.bepress.com/james_lock/74/ArticlesMie Scattering in the Time Domain. Part II. The Role of Diffractionhttps://works.bepress.com/james_lock/85/The p = 0 term of the Mie-Debye scattering amplitude contains the effects of external reflection and diffraction. We computed the reflected intensity in the time domain as a function of the scattering angle and delay time for a short electromagnetic pulse incident on a spherical particle and compared it to the predicted behavior in the forward-focusing region, the specular reflection region, and the glory region. We examined the physical consequences of three different approaches to the exact diffraction amplitude, and determined the signature of diffraction in the time domain. The external reflection surface wave amplitude gradually replaces the diffraction amplitude in the angular transition region between forward-focusing and the region of specular reflection. The details of this replacement were studied in the time domain. (C) 2011 Optical Society of AmericaWed, 01 Jun 2011 07:00:00 +0000https://works.bepress.com/james_lock/85/ArticlesMie Scattering in the Time Domain. Part I. The Role of Surface Waveshttps://works.bepress.com/james_lock/5/We computed the Debye series p = 1 and p = 2 terms of the Mie scattered intensity as a function of scattering angle and delay time for a linearly polarized plane wave pulse incident on a spherical dielectric particle and physically interpreted the resulting numerical data. Radiation shed by electromagnetic surface waves plays a prominent role in the scattered intensity. We determined the surface wave phase and damping rate and studied the structure of the p = 1, 2 surface wave glory in the time domain. (C) 2011 Optical Society of AmericaWed, 01 Jun 2011 07:00:00 +0000https://works.bepress.com/james_lock/5/ArticlesTransformation of Spherical Beam Shape Coefficients in Generalized Lorenz-Mie Theories Through Rotations of Coordinate Systems. V. Localized Beam Modelshttps://works.bepress.com/james_lock/96/<p>This paper is the fifth of a series of papers devoted to the transformation of <em><em>beam</em></em> <em>shape</em> <em>coefficients</em> <em>through</em> <em>rotations</em> of <em>coordinate</em> <em>systems</em>. These <em>coefficients</em> are required to express electromagnetic fields of laser beams in expanded forms, for use in some <em>generalized</em> <em>Lorenz</em>-<em>Mie</em> <em>theories</em>, or in other light scattering approaches such as Extended Boundary Condition Method. Part I was devoted to the general formulation. Parts II, III, IV were devoted to special cases, namely axisymmetric beams, special values of Euler angles, and plane waves respectively. The present Part <em>V</em> is devoted to the study of <em>localized</em> approximation and <em>localized</em> <em><em>beam</em></em> <em>models</em>, and of their behavior under the rotation of <em>coordinate</em> <em>systems</em>.</p>
Sat, 01 Jan 2011 08:00:00 +0000https://works.bepress.com/james_lock/96/ArticlesDebye Series for Light Scattering by a Coated Nonspherical Particlehttps://works.bepress.com/james_lock/68/By using the extended boundary condition method, the Debye series is developed for light scattered by a coated nonspherical particle in order to interpret the angular dependence of the scattered intensity in terms of various physical processes. Numerical calculations are performed to study the influence of the coating thickness and the ellipticity of a coated spheroid on the angular position of the alpha and beta primary rainbows, which are produced by partial waves experiencing one internal reflection. The hyperbolic umbilic focal section is demonstrated and is analyzed for both the alpha and the beta rainbows.Feng Xu et al.Mon, 14 Jun 2010 07:00:00 +0000https://works.bepress.com/james_lock/68/ArticlesDebye Series for Light Scattering by a Nonspherical Particlehttps://works.bepress.com/james_lock/50/The Debye series is developed for scattering of light by a homogeneous nonspherical particle to interpret the angular dependence of the scattered intensity in terms of various physical processes. In contrast to the previously developed Debye series for several regularly shaped particles that mirror the orthogonal curvilinear coordinate system where the variable-separation method can be applied, we develop and verify the Debye series in a coordinate-independent way using the extended boundary condition method. Verification computations are made for an oblate spheroidal water droplet of equivalent-volume sphere radius 10 mu m.Thu, 01 Apr 2010 07:00:00 +0000https://works.bepress.com/james_lock/50/ArticlesDebye Series for Light Scattering by a Spheroidhttps://works.bepress.com/james_lock/49/The Debye series is developed for electromagnetic scattering by a spheroid in order to decompose the far-zone fields into various physical processes. The geometrical rainbow angle and supernumerary spacing parameter are determined from the Debye intensity by fitting the results to an Airy function and comparing them to their assumed values in ray optics and Airy theory, respectively. Eccentricity-related scattering phenomena including the rainbow's angular shift, the disappearance of the rainbow, and the rainbow-enhanced glory are quantitatively demonstrated and analyzed. (c) 2010 Optical Society of AmericaThu, 01 Apr 2010 07:00:00 +0000https://works.bepress.com/james_lock/49/ArticlesOptical Caustics Observed in Light Scattered by an Oblate Spheroidhttps://works.bepress.com/james_lock/28/The electromagnetic fields scattered when a plane wave is incident on an oblate spheroid in the side-on orientation may be calculated using a generalization of Mie theory, and the results may be decomposed in a Debye series expansion. A number of optical caustics are observed in the computed scattered intensity for the one internal reflection portion of the Debye series for scattering angles in the vicinity of the first-order rainbow, and are analyzed in terms of the rainbow, transverse cusp, and hyperbolic umbilic caustics of catastrophe optics. The specific features of these three caustics are described, as is their assembly into the global structure of the observed caustics for spheroid scattering. It is found that, for a spheroid whose radius is an order of magnitude larger than the wavelength of the incident light, the interference structure accompanying the transverse cusp and hyperbolic umbilic caustics is only partially formed. (C) 2010 Optical Society of AmericaWed, 10 Mar 2010 08:00:00 +0000https://works.bepress.com/james_lock/28/ArticlesOptical Stress on the Surface of a Particle: Homogeneous Spherehttps://works.bepress.com/james_lock/12/A rigorous solution (generalized Lorenz-Mie theory) and an approximate solution (geometrical optics) are developed for the optical stress distribution on the surface of a homogeneous sphere. Demonstration calculations are made for plane-wave and Gaussian-beam illuminations. The influence of diffracted waves, surface waves, interference effects, caustic points, beam width, and refractive index on the stress is analyzed. The Debye series is used to evaluate the validity of geometrical optics and provides a quantitative analysis of the contribution of rays of different orders.Feng Xu et al.Fri, 01 May 2009 07:00:00 +0000https://works.bepress.com/james_lock/12/ArticlesRainbows in the Grass. II. Arbitrary Diagonal Incidencehttps://works.bepress.com/james_lock/24/We consider external reflection rainbow caustic,,; due to the reflection of light from a pendant droplet where the light rays are at an arbitrary angle with respect to the horizontal. We compare this theory to observation of glare spots from, pendant drops on grass; we also consider the potential application of this theory to the determination of liquid surface tension. (C) 2008 Optical Society of AmericaCharles L. Adler et al.Mon, 01 Dec 2008 08:00:00 +0000https://works.bepress.com/james_lock/24/Articles