Des Ondes Électromagnétiques qui ne Satisfont Pas aux Conditions d'Airy Peuvent se Propager dans les Lames Nématiques Hélicoïdales

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Abstract
G. B. Airy, in the year 1830, conceived a hypothesis for light propagation in an anisotropic and active medium: two privileged vibrations orthogonally polarized exist. Rigorously resolved, the electromagnetic equations of theories of active anisotropie media show two privileged waves polarized non orthogonally. All the crystalline rotatory powers known are too small for experimental observation. In twisted nematic films the twisting angle is limited to 90°, but the thickness can be arbitrarily fixed. For very small thicknesses the calculation gives a difference betwen ellipticities of two privileged waves attaining a few degrees. Thin layers of nematic phase of p[pacute] azoxyanisole are oriented between two edges of potassium chloride cleavage (100). Some zones with twisting angle of 90° exist. Between elliptical polarizer and analyser in a polarizing microscope with heating stage we can point privileged waves for sensitive tint. Significant differences of a few degrees between ellipticities are measured. Thickness of nematic layer is about 0.3μm.