Fig. 1. (a) Schematic illustration of the metaphotonic device with triatomic structural molecules for OPTP spectroscopy. The metadevice is probed by THz beams at normal incidence and excited by an optical pump at oblique incidence. (b) Unit cell of the metamaterial comprising a CW resonator, an LLMB, and two pairs of SRRs. The geometrical parameters are as follows: P_x = P_y = 100, w = 5, g = 4, q = 12, L₁ = 80, L₂ = 38, L₃ = 20, and L₄ = 17 µm. (c) Optical microscopic image of the metamaterials.

Fig. 2. (a) Experimentally measured THz transmission spectra of the metadevice at various pump-probe delays (as labeled). (b) Color map of THz transient transmissions against pump-probe delay and frequency.

Fig. 3. (a)–(d) Spectral dispersion of measured THz transmission for the triatomic metamaterials with a series of selected pump power levels (as labeled) at a fixed pump-probe delay of 6 ps for which the photo-induced change in spectral dispersion is maximized. (e)–(h) Corresponding numerically simulated transmission spectra varying with the conductivity of Si (as labeled).

Fig. 4. (a)–(e) Numerically calculated and (f)–(j) experimentally measured group delays of the THz waves transmitted through the metadevice for a series of conductivity of Si and pump power (as labeled), respectively.

Fig. 5. Simulated THz transmission spectra through (a) CW resonators, triatomic metamaterials (b) in the dark and (c) pumped by laser pulses. The conductivity of Si is selected as 10 S/m (in the dark) and 80,000 S/m (under laser pump). (d)–(f) Corresponding electric-field profiles in the triatomic metamaterial.

Fig. 6. Distribution of surface current density of metamaterials at resonance frequency. (a) Surface current at the transparent peak for σ_Si = 10 S/m (case without pump). (b) Surface current at the transparent dip for σ_Si = 80,000 S/m (case with the highest pump fluence).