Microwave and Millimeter-Wave Plasma Formation Within 2D Photonic Crystal Defects
crystals with integrated plasma elements have received increased attention in recent
years due to the variable nature of their dielectric properties. To date, all such
devices have included plasma elements that have been controlled using external power
sources, most commonly, DC discharge tubes. Recent modeling work by Gregório et al.
suggest that an electromagnetic wave ... read moreincident on a photonic crystal with a central
point-defect vacancy enables self-initiated gas breakdown. The vacancy left by the
point-defect creates a high-Q resonant cavity which enhances the electric field within
the cavity to the point of gas breakdown. Once breakdown occurs, the plasma is also
maintained within the vacancy by the incoming wave. In this thesis, I will explore the
environmental variables (gas pressure, input power) that allow for a plasma to be formed
and sustained, and the effect the plasma has on the incoming and outgoing
electromagnetic wave. Design parameters and experimental results of two photonic crystal
devices are included, one in the microwave frequency regime (~8.5 GHz) and one in the
millimeter-wave regime (~43 GHz). I demonstrate that self-initiation of a plasma within
the central vacancy is possible in 10 Torr of argon with as little as 1.4 W for the
microwave device and 40 Torr of argon and 1.5 Watts for the millimeter-wave device. Once
formed, the plasma filled cavity alters the transmission properties of the photonic
crystal device, reducing transmission by up to 30 dB depending on gas pressure and
power. Time domain measurements of plasma formation within the microwave device reveal
formation times 100 ns at 5 Torr and 9W and up to 3.5 µs at 50 Torr and 4 W. Plasma
formation time for the millimeter-wave device is as low as 180 ns at 400 Torr and as
high as 800 ns at 45 Torr. Using transmission of energy through the photonic crystal as
a diagnostic tool, electron densities of 1016 to 1017 m-3 are measured for the microwave
device and 1018 to 1020 m-3 for the millimeter-wave
Thesis (Ph.D.)--Tufts University, 2017.
Submitted to the Dept. of Electrical Engineering.
Advisor: Jeffrey Hopwood.
Committee: Thomas Vandervelde, Alan Hoskinson, and Robert White.
Keywords: Plasma physics, Electromagnetics, and Electrical engineering.read less