Light-induced displacement currents

At low frequencies, that is, for frequencies for which the wavelength of light is much larger than the largest dimension of the circuit, the current is the same everywhere in the circuit. In this case, the displacement current inside the material must be matched by an identical current in the external circuit used to maintain the potential difference across the sample. Thus one can observe the drift motion of the electrons inside the sample by monitoring the current induced in the external circuit. In our example, llie current is qv /L, or the product of the injected charge density with its average drift velocity normalized to the sample thickness. 

Light-induced ion diffusion across the membrane is not sufficiently fast to account for the short latency of ERP. The obvious alternative possibility is light-induced charge displacements. This conclusion is further supported by two experimental observations. Hagins and McGaughy found that the electric current associated with ERP satisfies the following condition ... 

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