A l'occasion du onzieme anniversaire de la decouverte de la premiere planete extrasolaire autour d'une etoile de type solaire, au moment ou environ 200 planetes ont ete decouvertes hors de notre propre systeme, de passionnantes questions a propos de leur formation, leur evolution et pour certaines d'entre elles, leur aptitude a abriter la vie, sont plus que jamais posees. Ces interrogations sur nos origines ont declenche l'emergence de nouveaux concepts technologiques et une tres forte volonte pour pousser les technologies existantes a leur limite, tout cela pour repondre au fantastique defi observationnel pose. ELTs, interferometres kilometriques au sol ou spatiaux, instruments de nouvelle generation: l'imagerie directe de systemes extrasolaires et leur caracterisation est sans conteste l'un des themes observationnels les plus exigeants, tout cela a cause de l'enorme contraste et de la minuscule separation angulaire entre les etoiles et leurs environements. Cette these est dediee a l'etude d'une classe de micro-composants bases sur la technologie des reseaux sublambda. Nous demontrons l'utilite des ces meta-materiaux integres et nano-structures dans le domaine de l'imagerie a tres grande dynamique. Les reseaux sub-lambda offrent en effet des solutions nouvelles et originales aux exigeantes contraintes induites par les objectifs scientifiques ambitieux de l'astrophysique a haut contraste. Apres avoir montre l'utilite pratique des outils coronagraphiques modernes dans l'observation de systemes planetaires en formation, nous presentons diverses solutions pour ameliorer la capacite de detection de systemes coronographiques existants, ainsi que de nouvelles totalement integrees et susceptibles de surclasser les systemes traditionnels au sein des instruments de nouvelle generation. Ensuite, toujours en profitant de la flexibilite optique des reseaux sublambda, nous proposons un nouveau concept de dephaseur achromatique pour l'interferometrie en frange noire, qui devra etre construit et teste dans le cadre des activites de R&D censees ouvrir la voie a d'ambitieuses missions d'interferometres spatiaux dedies a la detection et la caracterisation de planetes semblables a la Terre.

https://tel.archives-ouvertes.fr/tel-00147380/document

Réseaux sublambda pour l'imagerie et la caractérisation de systèmes planétaires extrasolaires

A previously reported two-reflection, undeviating-beam total internal reflection (TIR) quarter-wave phase retarder is optimized. The specifications and characteristics of the device are sensitive to the refractive index n of the rhomb material. In particular, the size of the rhomb can be reduced by a factor of 11 for the same aperture size if a glass with n = 1.70 is used instead of one with n = 1.53. Optimal conditions are in the refractive-index interval n = 1.68–1.71. Coated rhombs of this type are mentioned.

Optimization of a rhomb-type quarter-wave phase retarder

An achromatic device to rotate optical polarization by 90° is described. This is based on a series of reflecting surfaces that rotates incoming light about the optical axis and translates it such that the exiting light is collinear. Polarization rotation is achieved by rotation of the optical beam, as opposed to the more common approach of phase retardation by use of birefringent elements. For broadband operation from the UV to the near infrared, the device was constructed by use of total internal reflection in three fused-silica glass components. Losses are minimized with interstitial surfaces designed to be angled close to Brewster’s angle.

Low-loss ultrabroadband 90° optical rotator with collinear input and output beams

Phenomenological and mathematical analyses of oblique incidence in
total-internal-reflection phase retarders and the procedure for constructing
extremely achromatic quarter-wave retarders are presented. It is shown that
the retardance can assume the same value twice at two definite spectral lines.
As an example, a quarter-wave phase retarder is described that introduces a
retardance of exactly 90° at two He–Ne laser lines of 632.8 and 1150
nm with a maximum deviation of 0.007° for other wavelengths between these
two lines. This application is advantageous in conjunction with two-line and
multiline lasers where the radiation is usually pumped in a state of circular
polarization.

Theory of oblique-incidence phase retarders.

In the few exceptional cases of total internal reflection phase
retarders that are weakly sensitive to variations in the input angle of
incidence i, the devices are of increasingly larger size;
deviate or translate the emergent beam; are difficult to align in
optical systems; or, in coated rhombs, have an impermanent stability of
the retardance. Based on new compensating effects, novel devices of
high retardance stability and advantageous characteristics are
presented. One device is stable to within 0.09° of 90° for
i ± 3°. It is a two-reflection quarter-wave
retarder that does not alter the path of the compact size light beam,
is of compact size (one seventh the size occupied by the achromatic
device AD-1 for equal aperture lengths), and can be easily aligned in
optical systems or used as a rotating element. The path length of
the beam inside the device is less than one third the corresponding
length inside the achromatic device AD-1.

Phase retarders highly insensitive to the input angle

Results for three λ/4 phase retarders are reported. One of them is achromatic to within ±0.06° of 90° in the visible region. It is shown that, under certain conditions, oblique incidence on the entrance face of total internal reflection phase retarders can greatly improve the achromaticity.

N. N. Nagib

Papers

Phase retarders with variable angles of total internal reflection