Analysis of picosecond optoelectronic cross-correlation switches

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Abstract
We analyze the use of tandem, photoconducting gates in a biased transmission line for picosecond, optoelectronic cross-correlation measurements. In general the integrated photoinduced current is a function of the time delay between excitation pulses and is the sum of the cross correlation of the induced conductivities and a constant background. We consider two possible circuits, which differ in that one contains an isolation attenuator between the two switches which helps improve the contrast ratio of the cross correlation and dc outputs. We obtain the contrast ratios and the absolute outputs of the two circuits as a function of circuit parameters. We show that gate transmission saturation leads to distortions in the cross-correlation function and induced asymmetries which reflect the different functions performed by the two switches. Certain elements of the theory are compared with experimental results on the picosecond photoconductive response of semiconducting diamond. We, thereby, also illustrate the use of tandem photoconductivity gates in analyzing low resistivity semiconductors.