  Surface plasmon polaritons (SPPs) propagating along a waveguide working
electrode are sensitive to changes in local refractive index, which follow
changes in the concentration of reduced and oxidised species near the working
electrode. The real-time response of the output optical power from a waveguide
working electrode is proportional to the time convolution of the
electrochemical current density, precluding the need to compute the latter a
posteriori via numerical integration. The theoretical optical response of a
waveguide working electrode is derived, and validated experimentally via
chronoamperometry and cyclic voltammetry measurements under low power SPP
excitation, for various concentrations of potassium ferricyanide in potassium
nitrate electrolyte at various scan rates. Increasing the SPP power induces a
regime where the SPPs no longer act solely as a probe of electrochemical
activity, but also as a pump creating energetic electrons and holes via
absorption in the working electrode. In this regime the transfer of energetic
carriers (electrons and holes) to the redox species dominates the
electrochemical current density, which becomes significantly enhanced relative
to equilibrium (low SPP power) conditions. In this regime the output optical
power remains proportional to the time convolution of the current density, even
with the latter significantly enhanced by the transfer of energetic carriers.
