Temperature resistant anti-reflective coating on Si-wafer for long-wave infra-red imaging.

A micromachined Silicon lid, sealed by CuSn solid liquid interdiffusion bonding is a promising approach for hermetic sealing of microbolometers for use in low-cost thermal cameras. However, since ∼30% of long-wave infrared light is reflected at an uncoated single Si-air interface, anti-reflective treatments are required. Traditional anti-reflective coatings are inapplicable since CuSn solid liquid interdiffusion bonding requires heating to about 270 °C and these multi-layer coatings fail due to differing coefficients of thermal expansion for the different layers and the substrate.

Design and fabrication of AsS-based non-quarterwave multi-cavity Fabry-Perot filters with the laser-adjustable central wavelength.

We present a thorough study of the use of AsS thin films for the fabrication of high-performance multi-cavity bandpass filters. We show that such layers can be used inside a non-quarterwave multi-cavity Fabry-Perot structure to produce local changes of the central wavelength of the filter using photosensitive properties of this material. In particular, we study the impact of these index changes on the spectral performances of the filters and show how to adapt the design of the Fabry-Perot structures to produce a spectral shift without degrading the bandpass profile.

High-performance thin-film optical filters with stress compensation.

We present a thorough description of high-performance thin-film optical filters with high flatness. These components can combine several tens or hundreds of layers and are manufactured using plasma-assisted reactive magnetron sputtering. Stress compensation is achieved using dual-side coatings with appropriate spectral function.

Athermal compensation of the stress-induced surface deflection of optical coatings using iso-admittance layers.

Mechanical stress in optical thin films can induce surface deflection of optical coatings. In the case of a substrate coated on both sides, a method is proposed which can provide perfect cancellation of this deflection, independently of the deposition process or any other external parameter, such as the temperature sensitivity of the mechanical stress. It is straightforward to implement this method, based on iso-admittance layers, since the thickness of such layers can be used to freely compensate for deflection effects only, without having any influence on the film's optical properties.

Phase properties of high-reflectance two-material periodic mirrors: application to oblique-incidence tunable filters.

Mathematical expressions are developed for the phase-shift derivative with respect to the wavelength, in the case of nonquarter-wave, two-material, high-reflectance, periodic mirrors. These expressions are applied to the case of oblique incidence, and a condition relating the layer indices, which provides identical phase dispersion curves for both the P and S polarizations, is derived. The use of such mirrors in Fabry-Perot filters results in a common peak wavelength for both polarizations when the filter is used at oblique incidence, instead of the two separate spectral peaks usually observed.

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.

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.

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.

Design and Manufacture of Low-Absorption ZnS-YF(3) Antireflection Coatings in the 3.5-16-num 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.

Dedicated spectrophotometer for localized transmittance and reflectance measurements.

A dedicated spectrophotometer is built to achieve localized transmittance and reflectance measurements. The spatial resolution can be chosen from 100 microm to 2 mm, the spectral resolution from 0.5 to 5 nm, and the spectral range from 400 to 1700 nm.

Thin-film achromatic phase shifters for nulling interferometry: design approach.

Nulling interferometry in the thermal IR is the most promising technique for direct detection of Earth-like exoplanets. This technique requires a pi phase shifter for the parent star of the planet to be completely extinguished by destructive interference. We investigate how thin films can be used to design pi achromatic phase shifters.

Gradually layered alternated-substrate synthesis.

Gradually layered alternated-substrate synthesis (GLASS) is an automatic design method for optical coatings, which permits a gradual increase in the layer count of a stack while its optical properties are improved. This method does not require any starting design but only the design target and the list of allowed coating materials. In contrast to the needle technique, in which the coating is optimized between its two real external media, with new layers added inside the coating, the GLASS method adds new layers at the end of the design and uses coating materials as one external medium.

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.

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.

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.