An ultrafast probe for high-voltage pulsed measurements

Abstract

Summary form only given, as follows. This paper describes the latest advances that have been made in a programme to develop a high-voltage, high-bandwidth measurement probe, intended for use in the wide range of situations where the performance of more conventional probes is inadequate. A special purpose capacitive voltage divider made from ultra-high molecular weight polyethylene attenuates the high voltage, and feeds a Pockels cell that provides negligible loading on the output of the divider. Light from a laser diode is fed to the Cell through a long fibre optic cable, with the corresponding output signal being modulated by the voltage fed from the capacitive divider to the Pockels Cell. The emerging light is focussed into a further long fibre optic cable and on to a digital storage oscilloscope via a 1 GHz opto-electronic converter. The use of a finite-element package in the divider design ensures a compact and convenient shape, in which stray capacitance is minimised. Experimental results for 45 kV, 200 kV and 500 kV probes demonstrate that the rise time in response to an input pulse is less than 3 ns, 5 ns and 6 ns respectively, significantly better than that of a commercial high-quality electromagnetic probe.