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Holography is a long-established technique to encode an object’s spatial information into a lower-dimensional representation. We investigate the role of the illumination’s spatial coherence properties in the success of such an imaging system through point spread function and Fourier domain analysis. Incoherent illumination is shown to result in more robust imaging performance free of diffraction artifacts at the cost of incurring background noise and sacrificing phase retrieval. Numerical studies confirm that this background noise reduces image sensitivity as the image size increases, in agreement with other similar systems. Following this analysis, we demonstrate a 2D holographic imaging system realized with lensless, 1D measurements of microwave fields generated by dynamic metasurface apertures.

We review the foundations of transformation optics (the realization of a certain class of coordinate transformations through appropriate metamaterial design), from the perspective of covariant electromagnetic theory. Whilst reproducing the well-known parameter design for a spatial electromagnetic cloak, the covariant approach allows a greater design flexibility, in that coordinate transformation that explicitly include the time coordinate can be addressed. An example of the latter is the so-called spacetime cloak, in which events are concealed from distant observers through the manipulation of light's speed in both space and time. Covariant approaches have also yielded new insights to acoustics in which it has been shown that the underlying geometry of acoustic waves can be expressed as a (pseudo-)Riemanian metric in 4-dimensional spacetime. The role of the underlying velocity field of the medium is emphasized as a key and novel design parameter. The role of curvature in transformation theory is briefly reviewed. Finally, we speculate on the existance of a transformation formalism that can embrace several areas of physics.

It is known that the Fresnel wave surfaces of transparent biaxial media have four singular points, located on two special directions. We show that, in more general media, the number of singularities can exceed 4. In fact, a highly symmetric linear material is proposed whose Fresnel surface exhibits 16 singular points. Because for every linear material the dispersion equation is quartic, we conclude that 16 is the maximum number of isolated singularities. The identity of Fresnel and Kummer surfaces, which holds true for media with a certain symmetry (zero skewon piece), provides an elegant interpretation of the results. We describe a metamaterial realization for our linear medium with 16 singular points. It is found that an appropriate combination of metal bars, split-ring resonators, and magnetized particles can generate the correct permittivity, permeability, and magnetoelectric moduli. Lastly, we discuss the arrangement of the singularities in terms of Kummer's 166 configuration of points and planes. An investigation parallel to ours, but in linear elasticity, is suggested for future research. [ABSTRACT FROM AUTHOR]