The characterization and application of plasma-based photonic crystals for high power Terahertz devices.

Abstract

Plasma photonic crystals (PPCs) have the potential to significantly expand the capabilities of current submillimeter wave technologies by providing high speed (microsecond time scale) control of energy transmission characteristics in the GHz through low THz range. Furthermore, plasma-based devices can be used in higher power applications than their solid-state counterparts without experiencing significant changes in function or incurring damage. PPC studies on the unique conditions present in high powered applications are few. Furthermore, the construction of THz PPC experimental devices requires lattice sizes on the order of microns, plasma densities exceeding $10^{22}$ m$^{-3}$, and high power THz sources, all of which sit at the limit (or outside) of the capabilities of current technology. Analytical and numerical exploration of THz PPCs is therefore strongly motivated, allowing for advancements in understanding as hardware capabilities grow. In support of the use of plasma-based photonic crystals for high power THz wave applications, three complementary lines of research amenable to theoretical or numerical treatment are developed that account for plasma's unique properties. Plasmas do not have discontinuous density profiles; therefore, assumptions used for dielectric PCs are not valid and a new analysis is necessary. In the first line of investigation the effect of smooth versus discontinuous density profiles in PPCs on transmission characteristics is explored using a linear analytical model and group velocity band gap maps. Plasmas can deform in response to large electromagnetic fields. In the second line of investigation a two-dimensional plasma-vacuum photonic crystal is simulated using a high-fidelity plasma model, implemented in the discontinuous Galerkin finite element code WARPXM, and the plasma's response to high amplitude fields is observed. When the plasma in the PPC used for high power applications is partially ionized, changes in plasma density can occur due to energy absorption and ionization. In the final line of investigation, a reacting 5-moment multi-fluid model is implemented and applied to capture collisions and reactions for partially ionized THz plasmas.