Negative index metamaterials for particle acceleration and radiation generation

Frierson, William
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Metamaterials (MTMs) are engineered materials with remarkable applications. They unnaturally bend light via their intricate structures, rather than through some novel substance or chemical composition. MTMs are being used to develop, e.g., a superlens' (which has an optical resolution exceeding the theoretical limit) and a cloaking device (which effectively makes an object invisible by bending light around it). We investigated a MTM made by stacking parallel metal sheets, which have a periodic pattern called the complementary split-ring resonator (CSRR). Our computational models show how the CSRR MTM can accelerate charged particles and generate terahertz radiation (1 THz = 1012 Hz). Using numerical methods from COMSOL software, we simulated how the CSRR manipulates microwave light. The program looks for the CSRR's resonant frequencies of light and their corresponding oscillations (called modes). We first confi rmed previous results from Dr. Michael Shapiro at MIT, then continued to characterize the electrodynamic properties of the CSRR MTM. The CSRR MTM has one accelerating mode, which exists at frequencies between 5.34 GHz and 5.65 GHz (1 GHz = 109 Hz). The accelerating mode has a negative refractive index (NRI), where refractive index is a quantity based on the electric and magnetic properties of a material. MTMs are the only known materials possessing a NRI. We demonstrated the mode's NRI by approximating the CSRR as a periodic circuit, and extracted critical electrodynamic information. Finally, we examined how the CSRR MTM interacts with an electron beam, by simulating them simultaneously. We observed electron bunching,' which is a key property for the CSRR MTM's applications. The accelerating mode pushes and focuses charged particles along one axis. Eff ectively, the accelerating mode `kicks' the particles in one direction, and ensures they stay in a line. This action is highly desired for particle acceleration. Lastly, the CSRR MTM may be used to develop terahertz radiation devices, namely coupled-cavity traveling-wave tubes. Terahertz radiation generators are anticipated to usher in myriad advances in medical imaging, spectroscopy, and technology.