Jacqueline Begel

Modified MacNeille cube polarizer for a wide angular field

Well known relationships exist between thicknesses and indices of a stack of optical layers which permit the definition of very good polarizers of light. One of the most famous types of polarizer is the MacNeille cube. In this case the hypotenuse face of an isosceles right angled prism is coated with a polarizing deposit and then cemented to the hypotenuse face of an identical prism. This polarizer can be used over a large spectral range located in the s vibration stop band. Unfortunately, the insertion losses for thep vibration are large when the angular field is larger than +/-2 degrees . Using very simple optical considerations, we design suitable coating structures that allow the use of cube polarizers over a wide angular range, typically +/-10 degrees in air, when T(p)>0.97 and T(s) </= 10(-3). However, the spectral range is reduced. Diagrams are given to calculate the thickness of the layers according to the substrate and the indices of the evaporated materials. The prism angle is also determined to have a symmetric angular field in air. Such polarizers are suitable for semiconductor lasers because they can be used without a collimating lens in spite of their large divergence. Good optical characteristics up to T(p) approximately 0.95 and T(s) approximately 10(-4) over the range of +/-5 degrees have been measured for these polarizers manufactured in the Laboratoires de Marcoussis.

Thin film optical coatings. 7: Two-layer coatings close to antireflection

This paper examines the residual reflection of two-layer coatings close to antireflection. Residual reflection can be induced either by fluctuations or errors in the thickness of the layers. Fluctuations in thickness, resulting from insufficiently accurate measuring equipment, lead to the notions of stability and tolerances. When reflection is substantial, a method of calculation is proposed for determining thicknesses effectively deposited.

Infrared optical constant determination of weakly absorbing dielectric thin films

Simple approximate relations are given for the reflectance of a weakly absorbing dielectric layer deposited as a quarter wave or a half-wave upon transparent and metallic substrates. These approximated relations are used in the infrared to calculate the optical constants n and k and the inhomogeneity partial differentialn of the index n of a material deposited as a thin film. A high degree of accuracy is sought for k. Two examples are given for ZnS and ThF(4) in the 3-11-microm spectral range.