Conversion of electrostatic to electromagnetic waves by superluminous ionization fronts

The conversion of static electric fields to electromagnetic radiation by th e incidence of a superluminous ionization front on plasma is investigated. For extremely superluminous fronts, the radiation is close to the plasma fr equency and is converted with efficiency of order unity. A proof-of-princip le experiment was conducted using semiconductor plasma containing an altern ately charged capacitor array. The process has important implications in as trophysical plasmas, such as supernova emission, and to laboratory developm ent of compact, coherent, tunable radiation sources in the THz range.