Electromodulation of the Optical Properties of Gold

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Abstract
When a strong electric field is applied to the surface of a thin gold-film electrode in contact with aqueous electrolyte, we observe a change in the attenuated total reflection (ATR) spectrum of as much as 7%. The change was measured as a function of photon energy, angle to incidence, polarization, and electric field modulation frequency. It is shown that this effect is due to changes in the optical properties of the gold and not to changes in the electrolyte. The peak in this derivative ATR spectrum is at 2.5 eV, where the optical properties of gold are changing most rapidly with frequency. The effect is quantitatively explained by a shift in the optical constants of gold due to the change in electron concentration.