Demonstration of Microwave Generation from a Static Field by a Relativistic Ionization Front in a Capacitor Array.

Abstract

We present the results of a proof-of-principle experiment to demonstrate the generation of tunable radiation from a laser-ionize gas-filled capacitor array. This scheme directly converts a static electric field of wave number {ital k}{sub 0} into coherent radiation pulses of frequency {omega}{sup 2}{sub {ital p}}/2{ital k}{sub 0}{ital c}, where {omega}{sub {ital 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. {copyright} {ital 1996 The American Physical Society.}