Rafif E. Hamam

Design and global optimization of high-efficiency thermophotovoltaic systems

Despite their great promise, small experimental thermophotovoltaic (TPV) systems at 1000 K generally exhibit extremely low power conversion efficiencies (approximately 1%), due to heat losses such as thermal emission of undesirable mid-wavelength infrared radiation. Photonic crystals (PhC) have the potential to strongly suppress such losses. However, PhC-based designs present a set of non-convex optimization problems requiring efficient objective function evaluation and global optimization algorithms. Both are applied to two example systems: improved micro-TPV generators and solar thermal TPV systems. Micro-TPV reactors experience up to a 27-fold increase in their efficiency and power output; solar thermal TPV systems see an even greater 45-fold increase in their efficiency (exceeding the Shockley-Quiesser limit for a single-junction photovoltaic cell).

Broadband super-collimation in a hybrid photonic crystal structure

We propose a two dimensional (2D) photonic crystal (PhC) structure that supports super-collimation over a large frequency range (over 4 times that of a traditional square lattice of holes). We theoretically and numerically investigate the collimation mechanism in our 2D structure, in comparison to that of two other frequently used related PhC structures. We also point out the potential importance of our proposed structure in the design of super-collimation-based devices for both monochromatic and polychromatic light.

Extraordinary optical transmission through subwavelength holes in a polaritonic silicon dioxide film

The authors present experimental data showing that extraordinary optical transmission occurs through subwavelength holes etched in an amorphous silicon dioxide film. The discrete frequency ranges of the enhanced transmission suggest the involvement of surface phonon-polaritons in mediating the transmission in a manner analogous to surface plasmons on metal films. Finite-difference time-domain simulations also predict the enhancement and correlate well with the experimental data. Both experimental and theoretical results show a fivefold increase in transmission through a perforated film versus a solid film.

Purcell effect in nonlinear photonic structures: A coupled mode theory analysis

We develop a coupled mode theory (CMT) model of the behavior of a polarization source in a general photonic structure, and obtain an analytical expression for the resulting generated electric field; loss, gain and/or nonlinearities can also be modeled. Based on this treatment, we investigate the criteria needed to achieve an enhancement in various nonlinear effects, and to produce efficient sources of terahertz radiation, in particular. Our results agree well with exact finite-difference time-domain (FDTD) results. Therefore, this approach can also in certain circumstances be used as a potential substitute for the more numerically intensive FDTD method.