J. Phys. Radium
Volume 11, Numéro 7, juillet 1950
|Page(s)||366 - 372|
Méthode polarimétrique d'étude des couches minces par variation de l'indice du milieu d'incidence (immersion)F. Suhner
The author explains the method used for the study of thin polishing films and of artificial, transparent films on a transparent base, which is either isotropic (glass) or anisotropic (spar.). The incident beam of monochromatic, plane polarised light is reflected from the surface to be studied which can be immersed in liquids of varying refractive indices. The ellipticity produced in certain conditions is measured by means of a Chaumont analyser. The results obtained for each surface are interpreted by the simple hypothesis of an approximately homogeneous and invariable film, comparable to a simple layer. The very good agreement within the set of experimental values justifies this hypothesis and allows the calculation of reliable values for the refractive indices and thicknesses, both for polishing films and for the surface films obtained by chemical attack of glass. The experiments also confirm the analogy between the reflection from an isotropic substance, at incidence of varying obliqueness, and the reflection from a uniaxial crystal, observed normally in liquids of different refractive indices (the plane polarisation on reflection can be interpreted as a special case of optical continuity). In the case of oblique reflection from glass, the difference between Brewster's angle and principal incidence shows up clearly as soon as the thickness of the surface skin exceeds about one hundred Angstrôm units and becomes important for greater thickness. If, e. g., one wishes to make an antireflection film on glass by means of chemical attack, the observation of this simple factor allows to follow, step by step, the progress of the reaction, even in the acid bath. Analogous methods can be employed for studying transition films and films formed artificially at the interface between two liquids, and also for metallic reflection.
4279W - Optical coatings.
4225J - Polarization.
optical films -- light polarisation