Experiments concerning the nature of trapped-plasma mode harmonic extraction from P+-N-N+avalanche diodes

An experimental investigation has clarified the nature of both fundamental and harmonic extraction from p
⁺
-n-n
⁺
avalanche diodes operated in the trapped-plasma mode. A standard coaxial cavity was found to be suitable for low-order (
n\leq5
) harmonic generation. Calculations revealed that the circuit behaved as a bandpass filter which allowed power to be extracted at a particular output harmonic while "reactively" terminating the diode at other harmonics. Measurements were made of external current and
dV/dt
waveforms for illustrative cases of fundamental and low-order harmonic extraction. Integrated
dV/dt
waveforms exhibited overvoltages which increased with increasing peak displacement currents. In general, the duration of the plasma-removal period of high current increased with increasing overvoltage. Carroll's [16] suggested dichotomy of voltage waveforms into independent reactive and resistive components was found to be appropriate for optimum first and second harmonic extraction. For third, fourth, and fifth harmonic extraction, however, it was observed that optimum efficiency was associated with significant changes in the physical states of the diode. Fourier analysis of the integrated
dV/dt
waveforms for low-order harmonic extraction revealed that maximum voltage amplitudes occurred at the harmonic being extracted. Combination ridge waveguide coaxial cavities were used for high-order harmonic extraction in
X
and
K
band. A far-infrared interferometer detected components in the power spectrum from the
K
-band cavity at frequencies up to 40 GHz. It was found empirically that, to first order, the optimum observed extraction efficiency was equal to 50 percent/ (harmonic number).