Harmonics from a Microwave Gas Discharge†

Abstract

Harmonic power from a 10 cm wavelength glow discharge in neon has been detected down to 8 mm wavelength (18th harmonic). The fundamental power is fed from the waveguide to a coaxial line terminated by the discharge tube. A second smaller waveguide is coupled to the coaxial line to extract, the harmonic power. With careful matching at each wavelength, tho conversion loss appears to fall off by only 3-4 du per harmonic after an initial drop of 35 da to the third harmonic (lowest harmonic measured). A typical conversion loss from 10 cm to 8 mm (12th harmonic) is 63 dB, e.g. 20 kw input, 10 mv output. In general the output power increases with input power until arcing in the mount spoils the measurement. A pressure range of 5-39 mm Hg has been used.