We present the results of a proof-of-principle experiment to demonstrate the generation of tunable radiation from a laser-ionized gas-filled capacitor array. This scheme directly converts a static electric field of wave number $k_0$ into coherent radiation pulses of frequency ${\omega }_p^2{/2k}_{0}c$, where ${\omega }_p$ is the plasma frequency. The radiation frequency can be tuned by varying gas pressure and/or capacitor spacing. In this experiment, well-polarized, short (less than 5 ns) microwave pulses have been generated over a frequency range of 6 to 21 GHz. The frequency of the detected signal, as measured with cut-off waveguides, scales linearly with the plasma density, and the relative power of the signal scales quadratically with the dc bias voltage in agreement with the theory.

• Received 21 June 1996

DOI:https://doi.org/10.1103/PhysRevLett.77.4764