It is customary to evaluate the detecting ability of radiation detectors by stating the noise equivalent input power, or its reciprocal the detectivity, as a function of the modulation frequency. The statement is often given in terms of the detectivity D*, which is the reciprocal of the noise equivalent power referred to unit bandwidth and unit area.
But in this paper we are interested in the noise equivalent energy, not the noise equivalent power. The difference is more than a mere division or multiplication by time, because the noise equivalent power is usually given as a function of the modulation frequency of the radiation, whereas the noise equivalent energy must be given in terms of a pulse of radiation. The statement of the noise equivalent energy will be given in terms of the energy detectivity Δ*, which is the reciprocal of the noise equivalent energy referred to unit area of the detector.
It will be shown that the maximum possible energy detectivity is given by
This energy detectivity is, in fact, achieved if the radiation pulse is very short, and if the gain of the associated amplifier is suitably matched to the properties of the detector.
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