In this contribution I will review the relation between Statistical Optics and Free-Electron Laser theory. The active medium of Free-Electron Lasers is constituted by ultrarelativistic beams of electrons. In these beams, shot-noise is always present as a fundamental effect, and therefore an analysis in terms of Statistical Optics is needed to characterize the FEL system. I will underline the simplifying assumptions often made in statistical treatments and of FEL radiation, and discuss the definition of figures of merit used to describe the FEL output.
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