Signal detection mechanism from electron multiplier

Abstract

An electron multiplier, including an excitation means and collector, disposed in a high vacuum chamber and adapted to be coupled at its input to a charged particle analyzer is coupled through the vacuum chamber wall by a plurality of electrical feedthrough devices such that the excitation means is coupled to a high voltage power supply disposed outside the high vacuum chamber and the collector is coupled simultaneously through a capacitance coupling means and a resistance coupling means, both disposed within the high vacuum chamber, to an amplifier-discriminator and floating operational amplifier, respectively, both disposed outside the high vacuum chamber. The impedance offered by the capacitance coupling means is substantially lower than that offered by the resistance coupling to 10 nanosecond current pulses originating from single electron events. In the electron counting mode of operation the pulse signal from the amplifier-discriminator provides a measure of the input electron flux, but when the pulse count rate becomes extremely high, signal distortion due to pulse overlap occurs and a voltage-to-frequency converter driven by the operational amplifier means and an input-to-output electrical isolator provides an output signal from the analog mechanism representative of the input electron flux to the electron multiplier. Mechanism is also provided in the way of controlling the operation of the electron multiplier through a digital computer.