Terahertz optical activity and metamaterial properties of 2D array of metal-semiconductor microhelices

The terahertz optical activity of 2D arrays of metal-semiconductor microhelices was investigated by Fourier spectroscopy and free electron laser methods. We found strong resonance at first harmonic with wavelength twice helix length and weaker resonances at the second and third harmonics. The resonances are present in the transmittance, reflectance, and absorption spectra. For linear polarized radiation, a chirality of the media leads to their ellipticity at resonance frequency and rotation of the polarization plane in opposite directions (up to 16.5 degrees) on both sides of the resonance. It has been shown by direct interferometric method on free electron laser that the refraction index of the investigated layer has negative values for definite circular wave at certain frequencies. Its minimal value is -0.11.