Herschel Weil

Scattering and absorption of electromagnetic radiation by thin dielectric disks

The scattering and absorption of incident polarized radiation by thin flat circular disks composed of homogeneous isotropic material of complex refractive index is investigated by solving an integral equation for the induced currents. The method is particularly suitable for use in the resonant region where the free space wavelength is neither very small nor very large compared to the radius. Illustrative numerical results for bistatic total, and absorption cross sections for broadside, and edge-on incidence are given, using refractive indices for ice in the ir.

Radiation resitance of an elementary loop antenna in a magnetoionic medium

Radiation resistance for an elementary loop antenna immersed in a magnetoionic plasma is investigated. Based on an integral expression given by Kogelnik and Motz, extensive numerical results are obtained and their validity and utility are discussed. In addition a simple analytic expression is derived for the case of small magnetic fields.

Radiation resistance of an electric dipole in a magneto-ionic medium

Radiation resistance for an elementary electric dipole immersed in a magnetoionic plasma is investigated. Based on an integral expression obtained by Kogelnik, extensive numerical results are obtained and discussed. In addition a simple analytic expression is derived for the case of small magnetic fields.

A theoretical lunar ionosphere

The consequences of a mechanism originally used by Herring and Licht for computing a possible lunar ionosphere are investigated in more detail than was done by these authors. The mechanism assumes that protons of the solar flux which strike the moon are re-emitted as hydrogen atoms, some of which are reconverted to protons by charge exchange. There results a single layer ionosphere. In this paper simplifying assumptions made by Herring and Licht of complete spherical symmetry and an everywhere constant mean radial velocity for the emitted atoms are removed. Quite different procedures are then necessary and the effects of an incident flux coming from only one direction are brought out. For typical quiet sun solar stream parameters the resulting ionesphere has a single layer with a maximum electron number density of roughly 350 cm−3 at 0.6 lunar radii above the lunar surface on the moon-sun connecting line. There is only slow variation with angle of the radial location and magnitude of the maximum of the layer until about 60° off this direction; then rapid decreases in both location and magnitude begin. During times of enhanced solar activity the ionesphere according to this model would increase. However, the theory will likely not hold during storms associated with solar magnetic tongues.

Scattering and absorption by thin flat aerosols

An integral equation method is used to study spectral and polarization effects for the scattering and absorption of electromagnetic radiation incident on arbitrarily oriented flat disk aerosols of major dimension comparable to the wavelength of the radiation. Numerical results for flat plate ice crystals are presented.

Electromagnetic scattering and absorption by thin walled dielectric cylinders with application to ice crystals

Integral equations are developed to determine the scattering and absorption of electromagnetic radiation by thin walled cylinders of arbitrary cross section and refractive index. Numerical data are presented at wavelengths in the ir for hollow, circular, and hexagonal cross-section cylinders which simulate columnar sheath ice crvqtqls. The numerical nrocednree are economical for cylinders whose perimeters are less than about fifteen free-space wavelengths.

Integral equation method for scattering and absorption of electromagnetic radiation by thin lossy dielectric discs

Abstract An integral equation for the current induced in a dielectric body by incident electromagnetic radiation is solved for the case of a thin flat circular disc of homogeneous lossy dielectric material. The equation is reduced by using the method of moments to a linear algebraic matrix equation for the coefficients in an expansion of the current density as a linear combination of basis functions. The matrix elements consist of integrals involving the basis functions. The novel computational aspects of this work lie in the choice of basis functions and in the techniques which this choice enabled to handle singularities in the integrands when evaluating the matrix elements, to reduce the matrix size and to rigorously preserve symmetries in the matrix. Expressions are given for the scattering and absorption cross sections in terms of the expansion coefficients. The results are most suitable in the resonance range of wavelengths when the disc radius and free-space wavelength are of the same order of magnitude.

On the change in radar cross-section of a spherical satellite caused by a plasma sheath

Abstract A uniform neutral dilute ionized gas is assumed to be perturbed by a sphere moving through it. The radar return from the disturbed region is obtained by integrating the Compton scattering from the electrons, taking phase into account, but ignoring secondary scattering and attenuation. The electron density distribution for this computation is obtained by integration of the zeroth order velocity distribution function for neutral particles obtained by Wang Chang(6) as a solution of the Boltzmann transport equation. Numerical results are obtained for the perturbation of the electron distribution by a sphere travelling at 8 km sec and an altitude of 500 km and for the radar cross-section of this perturbed region when viewed broadside ∗

Disk scattering and absorption by an improved computational method.

A computer method for determining the scattering, absorption, and internal field structure of thin flat disks of arbitrary refractive index is described. The code is shown to be accurate for all angles of incidence for radii up to at least two free space wavelengths and for media ranging from pure dielectric to highly conductive ones. The accuracy of the method is assessed by comparison with published experimental data and with results computed by other methods. The applicability of this technique for analyzing clouds of disk-shaped aerosols is also discussed.

Saturation and secondary Stokes effects in coherent anti-Stokes Raman spectroscopy

Coupled differential equations are formulated to model the generation of coherent anti-Stokes Raman radiation in molecular gases. They include the basic coherent interaction of incident pump and idler (Stokes) waves to generate the anti-Stokes radiation plus other radiation and absorption processes which influence saturation due to population depletion of the lowest energy level. Other factors considered are simultaneous excitation of more than one vibration frequency, a quasi-monochromatic idler beam slightly off the true Stokes frequency, and the temporal laser pulse shape. Some effects of these various physical factors on saturation are presented graphically.