Left handed metamaterials at Terahertz frequencies

We report on three issues of left handed metamaterials targeting the terahertz spectral region (far- and mid-infrared). First, we show that it is possible to design a broadband negative index metamaterial by combining the respective advantages of current loops (the C-shaped pattern of split ring resonators) responsible of artificial magnetism and of continuous wires. Negative refraction was here demonstrated by angle-resolved experiments on a scaled model operating at X-Ku bands. Second, we evidence experimentally, around 0.3 THz, phase advance effects (backward waves) in transmission lines which were periodically loaded by series capacitances and shunt inductances. The experimental analysis is here conducted by using ultra-fast electro-optic sampling. At last, we consider two-dimensional C-shaped array operating at mid infrared (between 1000 and 3500 cm^-1). Under normal incidence, such a 2D array, comparable to a frequency selective surface, shows a magneto-electric response which was analyzed experimentally by FTIR measurements and numerically by field summation techniques.