 The first experiment using polarization analyzers with two exit channels, thus realizing the theoretical scheme envisaged in  Section 2,  was performed in the early 1980s with cascade photons from laser-excited calcium atoms by Aspect, Grangier, and Roger (1982). The outcome confirmed the predictions of quantum mechanics over those satisfying the Bell inequalities more dramatically than any of its predecessors, with the experimental result deviating from the upper limit in a Bell’s Inequality by 40 standard deviations. An experiment soon afterwards by Aspect, Dalibard, and Roger (1982), which aimed at closing the communication loophole, will be discussed in  Section 5.  The historical article by Aspect (1992) reviews these experiments and also surveys experiments performed by Shih and Alley, by Ou and Mandel, by Rarity and Tapster, and by others, using photon pairs with correlated linear momenta produced by down-conversion in non-linear crystals. Discussion of more recent Bell tests can be found in review papers (Zeilinger 1999, Genovese 2005, 2016).