Geometric Efficiency: A Complement to Quantum Efficiency in Imaging Detectors

Quantum efficiency is widely recognized as a key indicator of the performance of photon detectors, since it expresses the probability that an incoming photon will generate a measurable electrical signal. On its own, however, it does not reflect the limitations set by pixel geometry and the optical design of the system. In this work we therefore introduce a complementary concept, referred to as “geometric efficiency.” This term describes how much of the spatial and angular domain a pixel is actually able to capture compared to the theoretical maximum. In this way, geometric efficiency extends quantum efficiency by explicitly characterizing the geometric acceptance of detector pixels. A simple numerical example illustrates that this new measure allows the contributions of geometry and material properties to overall detector performance to be clearly separated. Taken together, geometric efficiency and quantum efficiency provide a compact and transparent framework for evaluating and comparing imaging detectors across spectral ranges, from X-ray to infrared and visible light.