5. Noise

Noise is any phenomenon that alters the quality of a signal. In the case of the detectors studied, the signal is an electrical one, and the main noises will also have an electrical origin.

There are two types of noise in a measurement system: fundamental or excess (non-fundamental). In the first case, noise is generated by the random displacement of charges in the circuit, and cannot be eliminated (e.g. thermal noise, shot noise). Excess noise is anything that has an ill-defined origin, the most important of which is 1/f noise. Fundamental noise is not frequency-dependent and is referred to as white noise. 1/f noise is particularly annoying at low frequencies, and is referred to as pink noise.