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We demonstrate how micromachined photonic crystals can be used to negatively refract terahertz frequency light. The photonic crystals, which are constructed from conventional dielectric materials, manipulate the incident beam via interaction with their photonic bands. Consequently, we show that different components of a broadband beam incident on the structure may be positively or negatively refracted, depending upon its frequency and that the structure can be used as an effective spectral filter of THz radiation.

Spontaneous emission enhancement is theoretically investigated in multiperiodic metal-dielectric multilayers (multiperiodic hyperboliclike metamaterials or photonic hypercrystals) where the unit cell consists of two layers of different dielectrics alternating with identical metallic layers. It is shown that the Purcell factor in such multiperiodic structures exceeds the Purcell factor in ordinary periodic hyperbolic or plasmonic metamaterials by a factor of 4, which in general makes it possible to maximize interaction between emitting centers and nearby plasmonic structures. This enhancement is numerically characterized and shown to be related to the interplay between surface and volume plasmonic excitations in the multilayer metamaterial. We separately identify the influence of proximity between the emitter and the closest metal-dielectric boundary (including the quenching effect and the enhanced coupling of the dipole radiation and surface plasmon polaritons) and the effects related to the structural composition of the hypercrystal. The Purcell-factor modification brought about by placing a cavity layer into a multiperiodic structure was also characterized. [ABSTRACT FROM AUTHOR]