Electromagnetic wave manipulation with plasma metamaterials
Keywords: Engineering.
Mechanical Engineering.

Metamaterial devices, the first examples of which appeared in the late 1990's, represent the cutting edge of electromagnetic wave manipulation. By creating these engineered materials, we can enhance antennas, create novel `superlenses', design cloaking devices, and reduce radar cross sections, among many other applications. As we move into the mid 2020's, metamaterial devices are being used to pursue even more exotic device functions such as optical computing, a new computing paradigm in which computation is performed with light signals as opposed to electronic signals. Optical computing devices, like matrix-vector multiplication accelerators and analog neural networks for classification and sequence processing, are a new frontier in optics where significant leaps forward can be made in speed and bandwidth when compared to conventional computing technology. This dissertation is focused on the use of plasma elements in metamaterial devices. Plasma has a unique electromagnetic response that is easily tunable, allowing for the construction of dynamic optical devices that are actively reconfigurable. This attribute of plasma makes it an ideal material for metamaterial devices that are designed to perform complex tasks such as optical computing since the functionality of the device need not be 'frozen-in' upon fabrication, leading to the possibility for more generalized, reconfigurable optical computing devices. The inclusion of plasma can also enhance and lend tunability to conventional optical devices. To explore the suitability of plasma metamaterial devices for these types of applications, we first conduct a search for complex device functionality in 3D plasma photonic crystal (PPC) devices and 2D magnetized plasma photonic crystal devices. A hybrid dielectric-plasma 3D photonic crystal bandgap device is constructed and the effects of the inclusion of a small number of under-dense plasma elements are studied. Although the effects are small, the transmission bandgaps of the device are shown to be reliably tunable in amplitude and frequency as the plasma density of the elements is varied. A 3D woodpile structure photonic crystal badgap device composed entirely of plasma elements is likewise constructed and tested, showing that polarization-dependent phenomena that cannot be simultaneously observed in 2D PPCs can couple together to produce enhanced performance of the device. After confirming the gyrotropic response of our plasma elements, we then proceed to produce 2D magnetized PPCs that exhibit topologically protected, backscattering immune one-way edge states and zero-index-medium behavior, leading to cloaking of embedded objects. To take advantage of these complex phenomena, we then moved to develop techniques for designing plasma metamaterials that do not need to rely on intuitive design. We use automatic inverse design methodology to produce plasma metamaterials (PMMs) with a simple 2D lattice structure that can perform the tasks of beam steering, demultiplexing, and even boolean logic with high efficacy. After confirming that the aforementioned devices were experimentally feasible by taking into account non-ideal factors like loss, nonuniform plasma elements, and experimental noise, we constructed the PMM experimental platform. First, we tested the optimal device configuration from the computational inverse design algorithm and found that the devices perform their intended function but not with very high efficacy. Because the plasma elements are dynamically tunable, fully in-situ inverse design of the devices is possible, and so an experimental optimization was performed, leading to a ~100x improvement on the computational inverse design configurations