There is provided a positron source for generating a positron beam. The positron source includes a laser arrangement configured to generate a beam of photons. A target is configured to receive the beam, wherein the target is arranged for the photons of the beam to generate a photon plasma at a surface layer of the target, wherein the surface layer is configured to preferentially absorb electrons from the photon plasma to generate corresponding free positrons. An electrode arrangement with one or more electrodes is configured to apply an electric field to the photon plasma to extract the free positrons therefrom and to guide the positrons to form the positron beam. At least the target and the electrode arrangement are included within a vacuum chamber configured in use to provide a vacuum condition in which the target and the electrode arrangement are arranged to function.

An energy converter is configured to convert photons into an output electrical signal, wherein the energy converter includes a laser arrangement configured to generate a beam of photons and a waveguide arrangement fabricated onto a substrate. The waveguide arrangement includes a plurality of waveguides configured to exhibit a non-linear optical effect, in which the plurality of waveguides are configured to receive the beam of photons and to bifurcate the beam into electron-rich photons propagating along one of the plurality of waveguides and into positron-rich photons propagating along another of the plurality of waveguides. An electrode arrangement having one or more electrodes are configured to apply an electric field to the electron-rich photons and the positron-rich photons to extract the output electrical signal therefrom. The energy converter may be, for example, included as a component part of a positron source for generating a beam of positrons.