Engineering the resonances of terahertz metamaterials

Abstract

Scope and Method of Study: The experimental tool used here in this investigation of terahertz metamaterials is a terahertz time domain spectrometer in which the transmitter and the receiver are photoconductive antennas driven and detected by femto second pulses. The terahertz pluse transmission through the different metamaterials was measured and analyzed by looking at the transmission spectrum and the phase change information. The metamaterial structures with minimum feature size of 2 microm were fabricated using conventional photolithography technique in a class 1000 clean room.

Findings and Conclusions: The main findings in this research has been the unique behavior of sub-skin depth metamaterials, the critical thickness at which they start showing signatures of resonant features and then ultimately saturating at twice the skin depth of the metal used. They also show a direct conductivity dependent behavior but suffer from huge radiation losses when the metal acquires a superconducting nature. The near field coupling in metamaterials gives rise to sharp resonant features with high Q factor which has the potential to be used for thin film sensing. Dielectric over layers of as thin as 100nm shows a notable shift in the resonances of the metamaterial. Destroying the periodicity of metamaterials does not affect its resonance properties significantly. Asymmetric coupling scheme results in a sharp transparency peak which mimics the quantum phenomena of electromagnetically induced transparency.