Classical and quantum Malus' law

The classical and the quantum Malus' Laws for light and spin are discussed. It is shown that for spin-1/2, the quantum Malus' Law is equivalent in form to the classical Malus' Law provided that the statistical average involves a quasi-distribution function that can become negative. A generalization of Malus' Law for arbitrary spin-s is obtained in the form of a Feynman path-integral representation for the Malus amplitude. The classical limit of the Malus amplitude for large s is discussed.