Figure 2: Experimental demonstration of chiral switching metamaterials.

(a,b) Scanning electron microscopy images of the fabricated metamaterial. The period of the metamaterial is 50 μm, which is far less than the wavelength of the terahertz waves. Scale bar in (a), 25 μm. In (b), the purple, blue and yellow colours represent the gold structures at different layers and the two silicon pads are shown in green. Scale bar, 10 μm. (c) The measured transmission spectra of LH (solid) and RH (dashed) circular polarizations, without (black) and with (red) photoexcitation. The shaded region represents the frequency range where the relative transmission amplitude between LH and RH polarization is reversed. (d) The CD spectrum (that is, ellipticity) and (e) the ORD derived from the measured transmission amplitude and phase spectra, without (black) and with (red) photoexcitation. In the shaded area, both the signs of CD and ORD are flipped, indicating the switching of handedness of the metamolecules. (f,g) The polarization states without (black) and with (red) photoexcitation for a linearly and vertically polarized incident terahertz beam transmitting through the chiral switching metamaterial at 1.0 and 1.1 THz, respectively. These two frequencies are also marked on the CD, and ORD spectra. At both frequencies, the polarization states turn from elliptical clockwise to elliptical anticlockwise under photoexcitation. Meanwhile, the major axis of the polarization ellipse is flipped from left to right at 1.0 THz, and from right to left at 1.1 THz.