A mechanism for generating coherent radiation of high power, variable duration, and broad tunability over several orders of magnitude from a laser-ionized gas-filled capacitor array is described. The scheme directly converts a dc electric field "wave" into a coherent electromagnetic wave train when a relativistic ionization front passes between the plates. The frequency and duration of the radiation is controlled by the gas pressure and/or capacitor spacing. Output frequency and power are calculated and compared to 2D particle-in-cell simulations.

• Received 21 January 1994

DOI:https://doi.org/10.1103/PhysRevLett.74.542