Richard D. Haracz

Scattering of light from arbitrarily oriented finite cylinders

An iterative approach to the scattering of light from a finite dielectric cylinder first developed by Shifrin and extended by Acquista is applied to cases where the phase shift is <2, and the cylinder is arbitrarily oriented. It is found that the first 2 orders of the iteration converge to within 1% when the aspect ratio (length/diameter) of the cylinder is as small as 20. The results are compared to the exact theory for infinite cylinders, and the effects of finite size are calculated and discussed.

Scattering of linearly polarized light from randomly oriented cylinders and spheroids

The Shifrin perturbation theory is applied to the scattering of light from finite cylinders and spheroids, and a procedure is described for averaging over the possible orientations of the symmetry axes of these various target shapes. The possible axis orientations of very long cylinders is limited by the conical shape of the scattering patterns, and the manner of taking this into account in the averaging process is detailed. It is found that the scattering intensities for the scattering of light from randomly oriented long cylinders, with aspect ratios (length/diameter) less than about 200, show differences compared with infinite cylinders of the same radius and dielectric constant (m=1.5). This is especially true for high and low scattering angles and when the plane of linear polarization is changed by the scattering. Moreover, the scattering intensities for the scattering of light from randomly oriented short cylinders and spheroids, with aspect ratios ranging from 0.1 to 10 and the same volume, show si...

Perturbation theory for scattering from dielectric spheroids and short cylinders.

The perturbation theory suggested by Shifrin is applied through the second order to the scattering of light from dielectric spheroids and finite cylinders. In the case of short dielectric cylinders, this technique provides an accurate prediction of the scattering pattern in its range of applicability, and this prediction is especially useful as no exact scattering solution exists. The validity of the perturbation theory is established by comparison with exact results for the spheroid, and excellent agreement is shown for ka(m − 1) ≈ 1, where k = 2π/λ, a is a representative target dimension, and m is the index of refraction. The results for the finite cylinder are refined from our previous work by a careful construction of the internal electrostatic solution. This allows the calculation of intensities for short cylinders. Comparisons are made between the spheroids and cylinders of equal volumes for aspect ratios ranging from ½ to 5, and significant differences are noted in some cases.

Scattering of linearly polarized microwave radiation from a dielectric helix

A method for calculating the electric field scattered from a helical dielectric target is compared to an equivalent experiment. The wavelength of the incident light is 3.18 cm, and the right-handed helix has a radius of 1.83 cm and wire radius of 0.24 cm, a pitch of 0.553 cm, and seven turns. The index of refraction of, the target is 1.626-i 0.012. A brief description of the Shifrin theory generalized to this application is given along with a discussion of the experiment, and the experimental intensities are compared to the first-order theory.

Light scattering from dielectric targets composed of a continuous assembly of circular disks

A technique for computing the electromagnetic fields scattered by spheres, cylinders, spheroids, spirals, toroids, and other targets which can be subdivided into circular disks is given. First-order calculations are performed for targets the size and refractive index of which preclude the creation of standing waves within the target. It is found that the scattering signatures of these various shapes are distinguishable for wavelengths larger than the target, but the differences rapidly diminish, as expected, with increasing wavelength. Finite cylinders are compared to prolate spheroids of equal volume, toroids are compared with oblate spheroids of equal volume, and calculations of the CIDS ratio for a spiral target are made for various wavelengths. It is found, on comparing these spiral calculations to other work on essentially 1-D spirals, that giving the spiral wire even a very small radius significantly affects the CIDS pattern for backscattering.

Angular scattering distributions by long copper and brass cylinders: Experiment and theory

Experimental measurements of electromagnetic radiation scattered by long copper and brass cylinders were performed in the IR spectral range (λ=10.6 μm). The cylinders were oriented essentially normal to the scattering plane. The results of the measurements were compared with the theory for infinite tilted cylinders modified for relatively large refractive indices. The good agreement is presented and discussed.

Scattering of linearly polarized microwave radiation from a dielectric target including the interaction between target elements.

The theory for finding the internal field within a dielectric helix when the radiation has a wavelength larger than the diameter of the helical wire is presented. Intensities are calculated and compared to an experiment and to the theoretical results of an earlier paper that does not include the self-interaction effect. The internal field is defined in terms of a polarization matrix that is assumed to be constant across any cross section of the helix. It is found that target self-iteractions have a significant effect on the internal field. It is also noted that this effect for the far field intensities, although significant and generally a better fit to the data, is not profoundly different. That is, the effects of a more appropriately constructed internal field are less important than the geometry effect in the far field.

Asymmetry factors for randomly oriented infinite cylinders

A method is presented for obtaining optical parameters that are relevant to problems of radiative transfer in such fields as polyester fiber insulation and the passage of radiation through aerosol clouds. The concept of the asymmetry factor is generalized to include nonspherical particles in order to calculate the ratio of the power of radiated light into the forward direction to the power of backscattering light. The geometry for scattering from an infinite cylinder randomly oriented is discussed and related to the problem of identifying the forward and backward directions. This geometry is used to calculate the asymmetry factor versus the angle which the cylinder axis makes with the direction of incidence. The asymmetry factor is also plotted as a function of the size parameter of the cylinder for random orientations of the cylinder.

Double scattering by randomly oriented long cylinders

Double scattering lidar events involving long cylindrical particles are discussed. The scatterers are allowed to be randomly oriented and the geometry required in the scattering solution is described in detail. The geometry is general, made to be applicable to any type of particle for which the single scattering matrix is provided, relative to the main axis of the scatterer. Results of the double scattering calculations are presented for the penetration of the lidar light into clouds of different optical depth τ (τ≤0.5).

Optimum two-body scattering T matrix elements on and off the energy shell for various potentials

Variationally optimized T matrices and phase shifts are reported for three potential scattering problems: (1) elastic scattering from a square well with a P state resonance, (2) elastic scattering from a Morse potential parameterized to fit S state nucleon–nucleon scattering data, and (3) off shell diagonal and nondiagonal scattering from the Reid potential. This last problem, involving a potential with long range attraction and short range repulsion, was selected for study because solving the three body problem within the context of the Faddeev formalism requires for input off shell two body T matrices arising from such a potential.