Optical orbital angular momentum transfer to electronic currents

Light orbital angular momentum (OAM) is transformed into an electronic current loop in a copper coil, by absorption of the optical radiation. The measurement of this current, that is in the 10⁻¹⁷ A range, makes it possible to evaluate and quantify the OAM carried by an electromagnetic wave in the optical domain. In particular, it determines unambiguously the torque generated by the beam and its topological charge. The induced current depends on the optical power and on the wavelength, in good agreement with theoretical predictions. Further possible developments towards an optical torque-meter are then discussed.