Basic Properties of Optical Detectors: Formalism and Characteristics

This lecture covers the fundamental properties of optical detectors, focusing on their formalism and noise characteristics. It begins with the output signal as a function of the input signal around a specific operating point, defining key concepts such as average value, offset, sensitivity, and non-linearity. The instructor explains how the average value is calculated over a defined integration time and how sensitivity is determined by the slope at the operating point. The discussion then shifts to responsivity, which is crucial for understanding detector performance, emphasizing that it does not indicate a detection limit due to the influence of noise. The lecture also introduces quantum efficiency, detailing its definition and factors affecting it, such as reflection and absorption. An example of quantum efficiency for different materials is provided, illustrating its variation with wavelength. Finally, the concepts of numerical aperture and angle of emission are discussed, explaining their significance in light collection efficiency and detector design.