Laetitia Abel-Tiberini

Masking mechanisms applied to thin-film coatings for the manufacturing of linear variable filters for two-dimensional array detectors.

We propose a method for manufacturing linear variable interference filters for two-dimensional (2D) array detectors, based on the use of correcting masks combining both rotation and translation movements of the masks and substrates. The major advantage of this method is its capability to produce several identical filters in a single run. 20 mm x 20 mm samples were manufactured with a wavelength ratio almost equal to 2 along the thickness gradient direction. In agreement with calculations, the measured uniformity perpendicular to the gradient is about 99.8% along 20 mm.

Optical characterization of an unknown single layer: Institut Fresnel contribution to the Optical Interference Coatings 2004 Topical Meeting Measurement Problem

We present the characterizations performed at the Institut Fresnel for the Measurement Problem of the Optical Interference Coatings 2004 Topical Meeting. A single layer coated on a fused-silica substrate of unknown composition and parameters is analyzed in terms of optogeometrical parameters, uniformity, and scattering. We determine the refractive index and the average thickness of the coating, then provide the localized determination of the thickness with a 2 mm spatial resolution. Topography measurements include atomic force microscopy and angle-resolved scattering measurements. These results are completed thanks to a Taylor Hobson noncontact 3D surface profiler.

Transmission behaviors of single mode hollow metallic waveguides dedicated to mid-infrared nulling interferometry

This paper reports the characterization of hollow metallic waveguides (HMW) to be used as single-mode wavefront filters for nulling interferometry in the 6-20microm range. The measurements presented here were performed using both single-mode and multimode conductive waveguides at 10.6microm. We found propagation losses of about 16dB/mm, which are mainly due to the theoretical skin effect absorption in addition to the roughness of the waveguides metallic walls. The input and output coupling efficiency of our samples has been improved by adding tapers to minimize the impedance mismatch. A proper distinction between propagation losses and coupling losses is presented. Despite their elevate propagation losses, HMW show excellent spatial filtering capabilities in a spectral range where photonics technologies are only emerging.

Manufacturing of linear variable filters with straight iso-thickness lines

Linear variables filters are band-pass multilayer coatings manufactured with a thickness gradient that allows a significant wavelength shift of the centring wavelength of the filter according to the point that is illuminated. In case such a filter is associated with a 2D matrix detector in order to form a compact spectrometer, iso-thickness lines must be as straight as possible, perpendicularly to the thickness gradient. To answer this problem, we developed a masking mechanism that combine the classical rotation movement of substrates and a translation movement for the mask, this last movement being induced during the rotation by the mean of a cam. Thickness gradient can be freely adjusted according to specifications, while transverse uniformity is 99.9%.

Dedicated spectrophotometer for localized transmittance and reflectance measurements

A dedicated spectrophotometer is developed for localized transmittance and reflectance measurements with a spatial resolution from 50 µm to 2 mm. Typical applications are related to thickness uniformity characterization and measurements of variable filters.

Spectrophotometric bench dedicated to the characterization of micro-patterned optical coatings

Characterization of the spectral transmission of micro-patterned optical coatings requires accurate and highly localized measurement means. However, the capabilities of commercial equipments are generally limited, and either they do not provide sufficient spatial and spectral resolution, or they modify the spectral transmittance properties of the sample by using a large half angle illuminating light cone. In this work, we propose a new approach based on the recording, using a high performance photodiode array camera, of monochromatic magnified images of the sample illuminated by a filtered and fiber-coupled super-continuum laser source. In such case, the spatial resolution is directly given by the size of the individual CCD pixels and by the magnification of the imaging objective, while the spectral resolution is defined by the slit width of the filtering monochromator. This paper will give a detailed description of the main features of this spectrophotometric bench, and will demonstrate its ability to record the spectral transmittance of patterned samples with micrometer spatial resolution and sub-nanometer spectral resolution in the visible and near infrared ranges.

Developing high-performance reflective coatings for the tunable filter and the high-order interferometer of the 3D-NTT

The following article describes the coatings of both Fabry-Perot (FP) etalons to be installed in the integral field spectrometer 3D-NTT. This simultaneous use of two FP etalons of high and low resolution respectively is the new concept upon which the 3D-NTT is built. Design and fabrication of the coatings of those etalons is a critical step to be able to achieve the desired performances of the instrument. More precisely, these etalons will have to show less than a 10% variation of the finesse from 370 to 900nm and a better than lambda/100 cumulative optical uniformity over a Ø100mm surface. The aim is thus to design high-reflectivity coatings for each of the FP etalon. The design process of the two sets of coatings will be described first, then the expected performances of each etalon will be presented and finally the progresses in the making of these coatings will be discussed.

A novel high-contrast imaging technique based on optical tunneling to search for faint companions around bright stars at the limit of diffraction

We present a novel application of optical tunneling in the context of high-angular resolution, high-contrast techniques with the aim of improving direct imaging capabilities of faint companions in the vicinity of bright stars. In contrast to existing techniques like coronagraphy, we apply well-established techniques from integrated optics to exclusively extinct a very narrow angular direction coming from the sky. This extinction is achieved in the pupil plane and does not suffer from diffraction pattern residuals. We give a comprehensive presentation of the underlying theory as well as first laboratory results.

Study of Ge 15 Sb 20 S 65 and Te 20 As 30 Se 50 Chalcogenide Coatings

We investigated high index chalcogenide thin films manufacturing by two deposition processes. Their physical and chemical properties have been compared to the bulk ones. First example of application to bandpass filtering is reported.