Frédéric Lemarquis

Simple layer-by-layer photonic crystal for the control of thermal emission

We present a theoretical and experimental study of a simple layer-by-layer photonic crystal structure designed for the control of the thermal emission in the infrared wavelength domain. We show that a relatively simple structure made of alternated ZnSe homogenous layers and gold microstructured grids can act as a thermal source itself giving us the unique opportunity to tailor its emission spectra. Comparisons between computed and measured transmission and emissivity spectra illustrate the relevance of our approach.

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.

Index determination of opaque and semitransparent metallic films: application to light absorbers

Index-determination methods based on reflectance and transmittance measurements are developed for both opaque and semitransparent metallic films. Results are given concerning chromium and nickel layers manufactured by electron-beam deposition. To take account of the evolution of the optical constants versus layer thickness, an inhomogeneous layer model is used, which permits us to obtain a good agreement between measurements and calculations. Results are applied to the design and manufacture of light absorbers for which accurate index knowledge is required. Measured absorption is higher than 0.999 on both broadband and monochromatic components.

Analytical achromatic design of metal–dielectric absorbers

Metal-dielectric coatings can be used successfully to design broadband absorbers. However, the understanding of the designs is not easy. Here we present a new analytical method using achromatic three-layer stacks. Such metal-dielectric basic structures permit movement from a fixed admittance value to another one over a wide spectral range. Efficient designs are calculated and explained with this method.

Design and manufacture of low-absorption ZnS-YF3 antireflection coatings in the 3.5-16-mu m spectral range

Broadband antireflection coatings on ZnSe substrates are designed and manufactured in the 3.5-16-mum IR range. The thin-film materials are YF(3) and ZnS produced by electron-beam deposition. To reach optimal performances to as great as 16 mum, we performed an accurate determination of complex indices, taking into account dispersion laws and absorption due to water within layers. With this knowledge, designs are optimized and absorption is reduced at 16 mum.

Infrared optical filters for the Infrared Atmospheric Sounding Interferometer meteorological space instrument

Optical coatings are designed and produced for the Infrared Atmospheric Sounding Interferometer meteorological space instrument operating in the spectral range 3.5 15.5 m. First we discuss the choice of substrates and determine the complex refractive indices of thin-film materials. Then several theoretical solutions are studied for optimizing the efficiency of the instrument. To allow us to study the feasibility of the coatings, a specific mid-infrared optical monitoring system has been developed. This system is validated by the successful manufacture of two-cavity Fabry Perot filters.

BUFFER LAYERS FOR THE DESIGN OF BROADBAND OPTICAL FILTERS

The use of buffer layers is a promising technique in the attempts developed for the design of optical multilayer coatings when two widely separated spectral regions are under consideration. Here we show that the buffer layer, associated with matching layers as in the application mentioned above, can also be exploited in a successive step process to broaden the spectral bandwidth of beam splitters or antireflection coatings.

Metal-dielectric light absorbers manufactured by ion plating

In order to improve their mechanic and climatic properties, we studied the manufacturing of metal-dielectric light absorbers using an Ion Plating Process. The choice of the materials, Hf for the metal and SiO2 for the dielectric, allows us of to use the deposition plant for either metal dielectric or all dielectric HfO2-SiO2 coatings without any change. After an index characterization of metallic films, we manufactured monochromatic and broad-band coatings. These coatings have been qualified for space environment.

Optical coating without phase dispersion for a Fabry–Perot interferometer

Phase dispersion induced by coatings can be a critical phenomenon in interferometry. We are interested in special mirrors intended for a Fabry-Perot interferometer with a high reflectance region and a low reflectance region in which phase dispersion on reflection must be avoided. We describe how a classical approach that uses the concepts of admittance and symmetrical multilayers allows the design of simple solutions.

Prototyping of differential optics for the SPHERE IRDIS dual imaging planet finder camera

The SPHERE (Spectro-Polarimetric High-contrast Exoplanet Research) planet finder instrument for ESOs VLT telescope, scheduled for first light in 2011, aims to detect giant extra-solar planets in the vicinity of bright stars by the aid of an extreme-AO turbulence compensation system and to characterize the objects found through spectroscopic and polarimetric observations. Dual imaging observations within the Y, J, H and Ks atmospheric windows (~0.95 - 2.32μm) will be done by the aid of the IRDIS cryogenic camera. Ensuring sufficiently low level of differential aberrations between the two parallel images is a major concern for this instrument. We describe the prototyping efforts made in order to validate our concept.