Michel Lequime

Chalcogenide coatings of Ge15Sb20S65 and Te20As30Se50

Chalcogenide coatings are investigated to obtain either optical components for spectral applications or optochemical sensors in the mid-infrared. The deposition of Ge(15)Sb(20)S(65) and Te(20)As(30)Se(50) chalcogenide glasses is performed by two physical techniques: electron-beam and pulsed-laser deposition. The quality of the film is analyzed by scanning electron microscopy, atomic force microscopy, and energy dispersive spectroscopy to characterize the morphology, topography, and chemical composition. The optical properties and optical constants are also determined. A CF(4) dry etching is performed on these films to obtain a channeled optical waveguide. For a passband filter made by electron-beam deposition, cryolite as a low-refractive-index material and chalcogenide glasses as high-refractive-index materials are used to favor a large refractive-index contrast. A shift of a centered wavelength of a photosensitive passband filter is controlled by illumination time.

All dielectric broadband mirror for Fabry-Perot interferometer

We present our first results on Fabry-Perot plates manufacturing with a broadband dielectric mirror on the front side and an antireflective coating on the rear face. Physical thicknesses of both coatings are optimized to reduce stress deformations.

Ultra fine measurement of the effect of a vacuum exposure on the central wavelength of narrow-bandpass interference filters manufactured by dual ion beam sputtering

Historically, the optical coating community has greatly improved the environmental stability of interference filters through the incorporation of energetic processes into the deposition chamber. This approach brought especially about a stabilization of their spectral features with respect to pressure changes, as occurring during the launching phase in space applications. The objective of our work was to quantify with a very high resolution (few picometers) the spectral shift under vacuum exposure of narrow bandpass filters manufactured by Dual Ion Beam Sputtering (DIBS). We will give first a description of the structure of these filters completed by a presentation of their manufacturing procedure, then a detailed description of our experimental set-up, and at the end a presentation of the results of our measurements on these two specific narrow bandpass filters.

Negative indices and the admittance formalism in multilayer optics

Negative indices are revisited through the thin-film admittance formalism. Emphasis is given to the anti-reflective behavior, the perfect lens and many other fascinating examples of application.

An Error Compensation Strategy for Broadband Optical Monitoring

We present a Broadband Optical Monitoring system which simultaneously measures reflectance and transmittance. The determination of coated thicknesses is integrated into a design software to optimize following layers. Experimental results are given.

New challenges in light scattering analysis of complex optical components (Conference Presentation)

Theory and experiment in the field of light scattering from optical coatings have been extensively studied and controlled since the 90’s. Indeed surface and bulk theories were developed for substrates and optical coatings, and have revealed great agreement with experiment. Furthermore, angle-resolved apparatuses were built with detection limits close to scattering from the air particles. All these tools have allowed to characterize roughnesses lower than 0.1 nm; also, the microstructure of thin film layers was investigated versus the deposition technologies. Nevertheless, in the last few years, new challenges for light scattering have merged. Actually, modern deposition technologies with their sophisticated monitoring systems today enable the deposition of large numbers of layers, hence providing complex filters which must be characterized at their working wavelengths or in a wide spectral region. Moreover an increasing demand for micro-structured filters has merged and requires new procedures to discriminate scattering from all micro-devices. In this context, we have developed in our group at Institut FRESNEL new numerical and metrological tools to satisfy these demands. All scattering facilities were rebuilt and upgraded, sometimes with strongly different principles. In this paper, we will present a rapid overview of these developments, with a focus on broad band scattering metrology (400nm-100nm) with no loss of performance, separation of intrinsic (surface profile) and extrinsic (local defects) roughness, and the control of large-angle scattering in ultra-narrow band filters. Examples and applications will be given to emphasize all improvements.

Complex pixelated optical filters

Multispectral or hyperspectral images allow acquiring new information that could not be acquired using colored images and, for example, identifying chemical species on an observed scene using specific highly selective filters.

Wide angle light scattering and complex optical filters: modelization and characterization

Because of their complexity (>100 layers) and their decreasing dimensions (~pixel size), performances of the new generation of optical filters for space application are degraded by wide angle light scattering. For these reasons, it is huge important to be able to predict and measure the angular and specral behaviour of light scattered by complex interferential filters. In this paper, light scattering is calculated for complex filters and take simultaneously account of most parameters: surface roughness, bulk inhomogeneity, cross-correlation coefficients, errors in design, wavelength and scattering angles (normal and polar), polarization… All these variations have become necessary to predict a balance in optical multiplexers and related systems, mainly for space applications. To complete the analysis, a metrological platform dedicated to the multimodal characterization of scattering losses has been involved.

Characterization and cleaning control of optical coatings by using a goniometric light scatter instrument with sample imaging ability

The principle of a new scattering measurement system including a mobile lighting and a fixed CCD array is described. This new system allows a spatially resolved light scattering characterization. Moreover it is possible to separate localized defects contribution from the local roughness measurement. The comprehensive characterization of optical coatings can be performed with this set-up, and some examples will be given.

Development of a real-time reflectance and transmittance monitoring system for the manufacturing of metaldielectric light absorbers

Metal-dielectric light absorbers are of great interest for suppressing stray light in optical systems. Such coatings can give an absorption level greater than 99.9% over a broad spectral range provided that the complex refractive index of metallic films is accurately known. For this purpose we developed a new real-time monitoring system that allows to measure in situ both reflectance and transmittance of the coating during manufacturing in the deposition chamber. This paper describes the system design and its characteristics and gives some preliminary results concerning metallic thin film characterizations.