Apparatus and methodology to measure the amplitude of oscillation of differential reflectivity from an electrode surface in contact with liquid with dissolved ions upon applying an oscillatory potential between the said electrode and the said liquid, where the differential reflectivity is a set of optical properties comprised of a change in intensity and phase of the oscillation of reflected light intensity relative to the incident light and a change in polarization of the reflected light. Analysis of the reflected beam may be used to determine various parameters of the electrochemical processes.