Figure 2

Evidence of resonance induced phase modulation.

(a) Applied field dependent relative phase response of the reflected terahertz wave, normalized with respect to the response observed without applying any external field. Phase response starts from 20.6 kHz with a phase reversal occurring at 20.8 kHz. Prominent field-dependent excitations are observed only in the frequency range of 0.1–0.5 THz, beyond which no significant response is observed (see inset). (b) Relative THz phase response plotted against the frequency of the applied external field. The relative phase response appears to exhibit a rippling surface-wave like behavior. The phase-shift is apparent at 0.259 THz and increases gradually until 0.276 THz. A sudden phase reversal relative to that at 0.276 THz was observed at 0.285 THz along with an indication of maximum response. For higher THz frequencies, the relative phase response flattens out and disappears completely beyond 0.302 THz. (c) Contour of the surface displacement profile measured with a vibrometer for excitation frequencies ranging between 19.2 kHz to 20.9 kHz. The surface displacement profile shows the maximum displacement of 108 pm at 20.7 kHz indicating it to be the regime of piezo-response along with rendering correspondence to (d), the THz phase response observed at 0.285 THz.