Charge transfer is provided to or from an electrically isolated test body by AC modulation of the photoelectric effect. More specifically, a reference body is disposed near the test body without physical contact between the reference and test bodies. Facing surfaces of the reference and test bodies are illuminated by optical radiation having a sufficiently short wavelength that charged particles are emitted from the reference and test bodies. An electrical bias is established between the reference body and the test body. Both the optical radiation and the electrical bias are modulated at the same frequency. A magnitude and direction of a charge transfer rate between the reference and test bodies is set by selecting a phase relation between the optical radiation and the electrical bias.