Manipulating Light with Metamaterials: Synchrotron Radiation from an Accelerating Light Pulse and On-Chip Devices

Abstract

Metamaterial devices which manipulate light over length scales that are not achievable with conventional optics are investigated. First, a sub-wavelength-slotted waveguide, which exhibits extraordinary transmission at a frequency near each of its Fabry-Perot resonances, is considered. We use THz-time domain spectroscopy to measure the transmission of a broadband test pulse through a structure designed to exhibit resonances in the 1-2 THz range. We demonstrate that light is transmitted at only a few frequencies which are determined by the tunable separation of the slotted plates. The wavelength-size of the structure makes it a candidate for on-chip THz spectroscopy platforms, which can allow for new applications in areas such as microfluidics and remote sensing. Limitations arising from the requirement for strict plate alignment are discussed, and future work entails the achievement of near-perfect (< 0.1°) parallelization of the plates. The next problem pursued in this work concerns the acceleration of light over hundred micron length scales in materials. Conventional methods for generating such accelerating beams involve setups which require length scales of at least several centimeters. Furthermore, Snell’s Law limits the ability of light incident from free space to bend at steep angles inside materials. For certain nonlinear crystals with high refractive indexes, it then becomes impossible to generate light beams that propagate along non-paraxial circular arcs. The use of metasurfaces to accelerate light eliminates all of these difficulties. We demonstrate the acceleration of light over length scales of one hundred microns inside a glass chip using metasurfaces consisting of plasmonic V-antennas. Future work involves the consideration of designs such as Huygens surfaces that would eliminate drawbacks associated with the V-antennas, but increase fabrication difficulty. This metasurface-approach is then used to accelerate a sub-picosecond light pulse over a hundred micron-scale circular arc inside a LiTaO3 crystal. Through mixing with the second order nonlinear susceptibility, the accelerating pulse produces a nonlinear polarization which emits synchrotron radiation. We image the evolution of the difference-frequency component of the synchroton field, which is at THz frequencies. This demonstration of synchrotron radiation over a scale of 100 µm is the smallest to-date. Calculations of the radiated power spectrum for a circulating charge suggest that synchrotron radiation produced from a continuously-revolving light pulse has implications for on-chip continuous-wave THz sources. One possible avenue for future work involves the use of whispering gallery resonators constructed from nonlinear crystals for the realization of monochromatic THz synchrotron radiation. Thus, each of the metamaterial devices presented in this thesis allow for both, the observation of physics that is interesting in its own right and the possibility of applications which benefit the broader scientific community.