This paper is a review of the theory-of laser beams and resonators. It is meant to be tutorial in nature and useful in scope. No attempt is made to be exhaustive in the treatment. Rather, emphasis is placed on formulations and derivations which lead to basic understanding and on results which bear practical significance.

Laser Beams and Resonators

This paper is a review of the theory of laser beams and resonators. It is meant to be tutorial in nature and useful in scope. No attempt is made to be exhaustive in the treatment. Rather, emphasis is placed on formulations and derivations which lead to basic understanding and on results which bear practical significance.

/pdf/laser-beams-and-resonators-3z6ox0w31g.pdf

Laser beams and resonators

We have developed a method for controlling electromagnetic surface wave propagation and radiation from complex metallic shapes. The object is covered with an artificial impedance surface that is implemented as an array of sub-wavelength metallic patches on a grounded dielectric substrate. We pattern the effective impedance over the surface by varying the size of the metallic patches. Using a holographic technique, we design the surface to scatter a known input wave into a desired output wave. Furthermore, by varying the shape of the patches we can create anisotropic surfaces with tensor impedance properties that provide control over polarization. As an example, we demonstrate a tensor impedance surface that produces circularly polarized radiation from a linearly polarized source.

Scalar and Tensor Holographic Artificial Impedance Surfaces

Implementation of abrupt phase discontinuities along a surface has been the theme of recent research on electromagnetic metasurfaces. Simple functionalities such as reflecting, refracting, or focusing plane waves have been demonstrated with devices featuring phase discontinuities, but optical surfaces allowing independent magnitude and phase control on the scattered waves have yet to emerge. In this paper, we propose the first true optical Huygens’ surface, which explicitly utilizes orthogonal electric and magnetic responses to realize total control on an optical surface’s local reflection coefficients. This extends the functionality of metasurfaces to an unprecedented level. We first demonstrate that a nanorod gap-surface plasmon resonator can act as a Huygens’ source. Thereafter, by properly tuning and rotating these resonators, we realize arbitrary reflection optical metasurfaces—surfaces for which the local reflection coefficients can be independently tailored in both magnitude and phase. We demonstrate the versatility of this approach through designs of a metasurface that asymmetrically reflects two copolarized beams and a Dolph-Tschebyscheff optical reflectarray.

Optical Huygens' Metasurfaces with Independent Control of the Magnitude and Phase of the Local Reflection Coefficients

The design and metrological applications of Fabry-Perot resonators in the microwave and millimetre regions of the electromagnetic spectrum are reviewed. The review opens with introductory discussions on open resonator principles and configurations, continues with an analysis of developments in theoretical and empirical resonator characterisation and concludes with a broad survey of recent microwave Fabry-Perot applications. These include dielectric, anisotropy, magnetic resonance, scattering and atmospheric measurements and gas refractometry and spectroscopy. Other applications discussed include quasi-optical filters and diplexers.

https://iopscience.iop.org/article/10.1088/0022-3735/15/1/002/pdf

Fabry-Perot and open resonators at microwave and millimetre wave frequencies, 2-300 GHz

Antennas having any mean surface and any prescribed feeder and radiation pattern can be experimentally obtained by the extension of the holographic technique to the microwave field. An experiment is described, based on the simple case of a plane antenna. Different types of microwave holograms, which constitute the synthesized antenna, have been tested.

http://ieeexplore.ieee.org/iel5/5/31115/01448762.pdf

Holographic antennas

The extension of holography to the microwave field, for the solution of problems such as antenna synthesis and construction of visible images of microwave illuminated objects, seems to be promising. In preliminary tests, the possibility of designing an antenna having any mean surface, any feeder, and any given radiation pattern by means of holographic technique, is shown. One of the practical problems which is encountered in microwave holography is the construction of the hologram, which requires the antenna to be synthesized. For this purpose, a series of holograms have been constructed and tested based on different approximations of the interference pattern. Another problem encountered is the presence of unwanted orders. Some preliminary tests on phase holograms show that this difficulty can be overcome simply by suitably varying the thickness of the hologram.

The integral equation of a “flat-roof resonator” is solved by the Fox and Li method of iteration in a number of particular cases.Mode patterns, phase shifts, and power losses are derived. A good overall agreement is found with the approximate theory previously developed by Toraldo di Francia.Some experimental tests carried out on a microwave model give a further confirmation of the theoretical predictions.

Modes, phase shifts, and losses of flat-roof open resonators.

The integral equation of a "flat-roof resonator" is solved by the Fox and Li method of iteration in a number of particular cases. Mode patterns, phase shifts, and power losses are derived. A good overall agreement is found with the approximate theory previously developed by Toraldo di Francia. Some experimental tests carried out on a microwave model give a further confirmation of the theoretical predictions.

Modes, phase shifts, and losses of flat-roof open resonators

The spatial impulse response functions of simple ionospheric models are computed using a ray-tracing technique. Such functions show measurable dependence on the single parameters characterizing the assumed profile. Hence the solution of the inverse problem (i.e., to determine the profile of the ionosphere from a measured impulse response function) seems feasible.

A. M. Scheggi

Papers

Holographic antennas

Holographic antennas

Modes, phase shifts, and losses of flat-roof open resonators.

Modes, phase shifts, and losses of flat-roof open resonators

Transfer functions of some ionospheric models