GENERATION OF MICROWAVE PULSES FROM THE STATIC ELECTRIC-FIELD OF A CAPACITOR ARRAY BY AN UNDERDENSE, RELATIVISTIC IONIZATION FRONT

The de to ac radiation converter is a new device in which a relativist ic ionization front directly converts the static electric field of an array of alternatively biased capacitors into a pulse of tunable radia tion. In a proof-of-principle experiment frequencies between 6 and 21 GHz were generated with plasma densities in the 10(12) cm(-3) range an d a capacitor period 2d=9.4 cm. In the present experiment, short pulse s with frequencies between 39 and 84 GHz are generated in a structure with 2d=2 cm. The frequency spectra of these pulses are measured using a diffraction grating. The spectra are discrete, and their center fre quency varies Linearly with the gas pressure prier to ionization (or p lasma density), as expected from theory. Their relative spectral width is around 18%, consistent with the expected number of cycles (six) co ntained in the pulses. An upper limit of 750 psec (bandwidth detection limited) is placed on the pulses length. The emitted frequency increa ses from 53 to 93 GHz when the capacitors are connected by pair to obt ain a effective array period of 4 cm. (C) 1998 American Institute of P hysics.