Recent Results on the Optoelectronic Feedback Preamplifier

A brief description of the optoelectronic feedback system is followed by an account of some interesting aspects of low-noise preamplifiers and detectors revealed by this work. These include the following items: 1. The observation of hole collection at the gate of a FET analogous to ion collection at the grid of a vacuum tube. 2. Mechanical failure modes of light-emitting diodes when cycling their temperature to and from 77°K. 3. A counting-rate effect due to the mean current in the feedback path. This naturally leads to a philosophical discussion of the equivalence of resistor and light-coupled feedback systems. It also suggests the potential advantages of using a pulsed, rather than dc, feedback system. We also report the use of the optoelectronic feedback system for the observation of a Fano factor of .08 or less for a germanium detector.