Physical Optics Field Research Articles

Singularity expansion representations of fields and currents in transient scattering

A unified treatment of the natural mode representations for induced currents and scattered fields is obtained by use of fundamental concepts regarding causality and superposition. The transient scattered field response is shown to have the form of a constant coefficient complex exponential sum only in the "late-time," after the last driven reponse is received from the object. Prior to this, the "early.time" response is found to be due to direct physical optics fields as well as a sum of temporally modulated natural modes produced by the progressive illumination of the incident wavefront. Alternate representations and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</tex> -plane behaviors are considered. The implications of these results on natural resonance target identification schemes are discussed.

Physical optics approach for scattering by thin helical wires

A physical optics formulation of scattering by thin wire helices of finite and infinite extent is presented. The high frequency limit of the integral representation of the physical optics field is obtained by the saddle point technique and is shown to be identical to the field computed by the geometrical optics approximation. For thin wire helices of finite extent, the physical optics approximation to the current should be supplemented by current waves traveling along the wire that are excited by the discontinuities at the ends of the wire. This modified physical optics approach is found to be a useful approximation to compute scattering by nonresonant helices that have a larger pitch than approximately 5 wavelengths. A hybrid method composed of the modified physical optics technique and the method of moments is applied, for the degenerate case of a linear wire, in order to extend the region of validity to cover the resonant cases. The modified physical optics approach is typically 5–10 times faster than Galerkin's method, and most important, it provides physical insight into the scattering phenomenon.

Hamiltonian analysis of beams in an optical slab guide

The formal analogy between Hamiltonian classical mechanics and quantum mechanics on the one hand and geometrical optics and physical optics on the other hand is systematically presented. When the time is replaced by the axial coordinate of a cylindrically uniform optical system and Hamilton’s principle replaced by Fermat’s principle, classical particle trajectories correspond to rays and quantum-mechanical wave functions to physical-optics fields. The operator formalism of quantum mechanics then provides elegant solutions for problems associated with propagation of beams in a gradient-index multimode optical slab guide.

Scattering by a dielectric wedge: A numerical solution

A numerical method is presented for the scattering by a general penetrable wedge. A set of coupled integral equations may be forumlated from Maxwell's equations, Green's theorem, and boundary conditions. The numerical solutions to the unknown surface fields on the boundary are first obtained by flat-pulse expansion for the fields near the tip and physical optics fields away from the tip and then point matching. Results are presented for a right-angled lossless dielectric wedge illuminated by a TE incident plane wave. The analysis should prove useful for extending the ability of GTD methods to handle dielectric wedge tips.

The physical optics of focused scatterers using source multipole expansions

A multipole-expansion technique is developed which permits the two-dimensional scattering integral for reflector antennas to be replaced by a finite sum of simple algebraic terms. The series, which accurately represents the radiated field over the main antenna beam and first few sidelobes, converges rapidly because the source dimensions are small. It is demonstrated that the reciprocity theorem is satisfied by the boresight physical-optics field of a paraboloid illuminated by a generalized linear electric current feed centered at the focus.

Experiments in Physical Optics

M Francon, N Krauzman, J P Mathieu and M May London: Gordon and Breach 1970 pp xii + 211 price £5 The field of physical optics lends itself to demonstration experiments more readily than perhaps any other branch of science. In view of the current tendency to stress mathematical formalisms at the expense of observation of phenomena in our physics courses, it is to be specially welcomed that a group of distinguished workers in the field of physical optics have taken the trouble to collect in book form their experience in setting up class and lecture demonstrations.

Introduction to Modern Optics

G. R. Fowles London: Holt, Rinehart and Winston. 1968 Pp. x + 304. Price £5 12s. The subject matter covered by this book is divisible into the two fields of physical optics, as represented by chapters entitled 'The propagation of light', 'The vectorial nature of light', 'Coherence and interference', 'Diffraction' and 'Optics of solids', and quantum aspects of optics, as represented by chapters entitled 'Thermal radiation and light quanta', 'Optical spectra' and finally 'Amplification of light, lasers'. A comparison with previous textbooks of optics indicates that the manner of presentation of the material is distinctly modern and that some of the topics included within the chapters unquestionably fall within the category modern optics.

Optics in Czechoslovakia

After a brief description of the historical development of optics in Czechoslovakia, a short survey of its present state is given. Research in the fields of image forming, physical, physiological, spectroscopic, and molecular optics carried out at the Czechoslovak Academy of Sciences, in the universities, and in industrial research institutes is described. Brief mention is also made of the optical industry and the training of opticists.

Numerical approach for predicting radiation patterns of HF-VHF antennas over irregular terrain

The feasibility of using a direct numerical integration of physical optics fields for computing radiation patterns of ground-based HF-VHF antennas in the presence of known ground irregularities is examined. The initial study treats a special case of a line source above a perfectly conducting plane with a semicylindrical boss. This case permits a comparison of results computed using physical optics formulations to the exact values. The agreement is gratifyingly close, which justifies an extension of such a study to a three-dimensional case.