Knowledge Bank

The third and higher harmonics of the 3031 magnetron ($\lambda =1.25cm$) are being used as the radiation source for dielectric constant measurements. The harmonic power is a function of both the magnetic field strength and of the keying voltage, the optimum combinations of these parameters being somewhat different for each harmonic and each magnetron. A 15-inch spectrometer employing an echelette grating in a $Greig-Ferguson1$ mount is used. The detector is a Wollaston wire bolometer in guide followed by a lock-in amplifier and Esterline-Angus recorder. The signal-to-noise ratio is greater than 1000 at third harmonic and falls to approximately 50 at seventh harmonic. Index of refraction is computed from measurements of the complex amplitude transmission coefficient, the computation being done by an interation procedure.