Jacques Mouchart

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.

Stabilisation Spectrale Des Dépôts Optiques en Couches Minces

Abstract La connaissance des derivees spectrales du coefficient de reflexion en energie R dun depot optique en couches minces permet de mieux comprendre linfluence que celles-ci exercent sur la valeur de la reflexion. Dans certaines conditions il est possible dagir sur ces derivees pour modifier la forme de la courbe spectrale en reflexion ou en transmission. En particulier lannulation des derivees spectrales successives determine des revetements dont la reflexion R reste constante sur tout un domaine spectral de longueurs donde (traitements large bande). Dans cet article on donne les expressions generales permettant de calculer les deux premieres derivees spectrales de R quand les epaisseurs optiques sont quelconques. Un raisonnement simple montre quon peut remonter jusquaux derivees dordres superieurs sans calculs supplementaires quand le revetement est antireflechissant ou constitue de couches en λ/4. On deduit les conditions que doivent verifier entre deux indices et epaisseurs des couches pou...

Dépôts Achromatiques Partiellement Réfléchissants

Abstract Dans le domaine des filtres interferentiels, les traitements achromatiques partiellement reflechissants jouent un role important en tant que composants optiques. Comme cest le cas pour la majorite des depots, ils peuvent etre definis a partir de methodes delaboration tres diverses: ceci conduit parfois a lobtention de filtres de caracteristiques optiques similaires bien quils aient des structures propres tres differentes. Le choix de la meilleure solution se fait alors suivant des criteres de reproductibilite et de facilite de fabrication.

Mesure de la reflectance de miroirs metalliques dans l'infrarouge

The performance of high power CO(2) lasers depends directly on the quality of the metallic mirrors used. The mirrors are therefore the key elements of these lasers and must have a reflectance as near as possible to unity. Thus, we have to characterize these mirrors precisely, that is to say, to use suitable measurement methods to determine their optical properties with enough accuracy. In this paper we describe a reflectance measurement system based on the use of a classical spectrophotometer. This method gives relative measurements, but with the help of a known standard reflectance, we can obtain the absolute value. Experimental results show that the accuracy is ~1-2.5 x 10(-4) provided that many measurements are made and precautions are taken. We propose here to study these conditions and in particular to give the reflectances of metallic mirrors at 10.6 microm.

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.

Réflectance Spectrale Minimale des Dépôts Optiques en Couches Minces

Abstract Le minimum de reflectance dun depot optique de configuration preetablie—cest a dire ayant un nombre de couches maximum fixe et des materiaux dindices determines—peut dans certains cas ne jamais etre nul a une longueur donde donnee λ, quels que soient le positionnement des couches dans lempilement et la valeur de leurs epaisseurs. Dans ces conditions, le minimum absolu de reflectance est a rechercher necessairement parmi les structures dont les couches sont toutes en pλ/4, p etant un entier positif ou nul. Cette propriete est appliquee aux traitements en une, deux, trois couches et plus, au voisinage de la reflectance nulle. Elle permet detendre le diagramme de Vlasov-Schuster relatif aux antireflets a des depots a faible reflectance residuelle.