Coherence and interference play an important role in classic and quantum physics. Processes to be employed can be significantly enhanced and the unwanted ones suppressed through the deliberately tailored constructive and destructed interference at quantum transitions and at nonlinear optical (NLO) coupling of waves in bulk materials. Phase matching of the coupled waves at different frequencies is the requirement of a paramount importance for frequency conversion and energy harvesting of the electromagnetic waves by the means of NLO. Unusual beneficial NLO processes were predicted at the coherent coupling of ordinary and extraordinary backward electromagnetic waves (BWEMWs). Energy flux and phase velocity are counter-directed in BEMWs. Herewith, we show that deliberately engineered spatially dispersive metamaterial slab can enable the co-existence and phase matching of contra-propagating ordinary fundamental and extraordinary backward second harmonic surface electromagnetic modes. We show that frequencies, phase, and group velocities, as well as nanowaveguide losses inherent to the electromagnetic modes supported by such metamaterial, can be tailored to maximize frequency conversion and to reverse propagation direction of the generated wave. Such a possibility in THz is proved with a numerical model of the hyperbolic frequency-doubling metareflector made of carbon nanotubes standing on the metal surface. The possibility to extend this approach to other coherent NLO processes and materials will be discussed too.
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121 Burton Morgan, Purdue University, West Lafayette, IN