Influence of structural symmetry on resonant property and optical sensitivity in terahertz metamaterials

By utilizing optical pump terahertz probe spectroscopy we have investigated four samples with terahertz subwavelength structures, which derived from split ring resonators. The experimental results show that adding the same length bar in the middle of the symmetric samples has less influence on resonant properties. However, asymmetric samples could present coupling and splitting effect in transmission spectra. Additionally, compared with the symmetric structures the asymmetry structures are more sensitive to pump excitation. Under pump excitation for different resonant mechanisms, we find the LC resonance has higher sensitivity than dipole resonance to the pump excitation. Our obtained results indicate that the photogenerated carriers in the substrate play a very important role in optical modulation properties.