Figure 2.

Contributions of the fast picosecond and slow thermal response to the optically driven IMT in VO₂ and antenna–VO₂ hybrids. (a) Time-dependent response of VO₂ (top, λ_probe=1600 nm) and antenna array with L_v=L_h=210 nm (bottom, λ_probe=1200 nm) for repetition rates of 0.2 MHz (red), 0.5 MHz (green), 1 MHz (blue), 2 MHz (magenta), 5 MHz (brown) and 10 MHz (orange). The effect before 0 ps corresponds to a slow heat background, with the step at 0 ps corresponding to single-cycle fast switching caused by picosecond phase transition. Pump energy P_pump for the VO₂ film, 4 nJ; for the antenna array, 0.2 nJ. (b) Relative contributions of single-cycle fast ΔOD_fast/ΔOD and slow heat background ΔOD_slow/ΔOD (see text) obtained from the time traces in a. The antenna array shows 5× increased operating speed for single-cycle fast switching compared with pure VO₂. (c) Phase-change modulation ΔOD/OD versus optical pulse energy at λ_probe=1200 nm for the antenna array and at λ_probe=1600 nm for the VO₂ film, both at 0.1 MHz. The blue shaded region indicates the damage threshold for the antenna array. (d) Differential nonlinear response spectrum ΔOD/OD_Ant for an antenna array with L_v=L_h=210 nm, for different combinations of pump (magenta arrows) and readout (black/red arrows, horizontal, green/blue arrows, vertical) polarizations, at a temperature of 50 °C, 0.1 MHz pump laser repetition rate, and 0.6 nJ pump energy.