  In 1822 A. Fresnel described an experiment to separate a beam of light into
its right- and left- circular polarization components using chiral interfaces.
Fresnel's experiment combined three crystalline quartz prisms of alternating
handedness to achieve a visible macroscopic separation between the two circular
components. Such quartz polyprisms were rather popular optical components in
XIXth century but today remain as very little known optical devices. This work
shows the analogy between Fresnel's experiment and Stern-Gerlach experiment
from quantum mechanics since both experiments produce selective deflection of
particles (photons in case of Fresnel's method) according to their spin angular
momentum. We have studied a historical quartz polyprism with eight chiral
interfaces producing a large spatial separation of light by spin. We have also
constructed a modified Fresnel biprism to produce smaller separations and we
have illustrated the process of weak measurement for light. The polarimetric
analysis of a Fresnel polyprism reveals that it acts as a spin angular momentum
analyzer.
