Figure 3: Giant electric modulation of SFG process. (IMAGE)
Caption
a Energy level diagram of SFG process. Two-photon excitation with mid-IR (ω1) and near-IR (ω2) light induces radiation at the sum frequency of those light (ωSFG=ω1+ω2) b Schematic depiction of the near-field SFG experiment using a Au tip and a Au substrate mounted on an STM unit. c TE-SFG spectra obtained at sample biases of 0.25 V (cyan), 0.5 V (sky blue), and 0.75 V (dark blue) with a constant tunnelling current setpoint of 250 pA. The black curve indicates the signal obtained when the tip and the substrate were retracted enough (30 nm) to deactivate the plasmonic enhancement effects. d Two-dimensional plot of TE-SFG spectra obtained with the various applied sample bias under the almost constant tip-substrate distance (d~7 Å). e The voltage-dependent change in the TE-SFG output (ΔITESHG (V)) normalized by the TE-SFG signal intensity at V = 0 V (ITESHG (V = 0)) is depicted by blue open circles. The orange curve is the result of curve fitting with a quadratic function.
Credit
Adapted from Takahashi et al. (2026), Nature Communications
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License
CC BY