Wavelength-scale stationary-wave integrated Fourier-transform spectrometry

Spectrometry is a general physical-analysis approach for investigating light-matter interactions. However, the complex designs of existing spectrometers render them resistant to simplification and miniaturization, both of which are vital for applications in micro- and nanotechnology and which are now undergoing intensive research. Stationary-wave integrated Fourier-transform spectrometry (SWIFTS)-an approach based on direct intensity detection of a standing wave resulting from either reflection (as in the principle of colour photography by Gabriel Lippmann) or counterpropagative interference phenomenon-is expected to be able to overcome this drawback. Here, we present a SWIFTS-based spectrometer relying on an original optical near-field detection method in which optical nanoprobes are used to sample directly the evanescent standing wave in the waveguide. Combined with integrated optics, we report a way of reducing the volume of the spectrometer to a few hundreds of cubic wavelengths. This is the first attempt, using SWIFTS, to produce a very small integrated one-dimensional spectrometer suitable for applications where microspectrometers are essential

Intégration d'un micro-spectromètre statique par transformée de Fourier sur un plan focal infrarouge

Aujourd hui, les progrès importants en microtechnologie permettent de réaliser des détecteurs infrarouges matriciels de grand format, appelés plans focaux infrarouges (PFIR), qui sont intégrés dans des imageurs. On étudie maintenant la possibilité de réaliser des imageurs permettant de résoudre spectralement une scène pour en extraire une information sur quelques bandes (imagerie multispectrale). Un moyen de répondre à ce besoin est de réaliser des PFIR multispectraux. Même si la faisabilité de PFIR bispectraux a déjà été démontrée en France, il est difficile, voire impossible, d envisager des PFIR multispectraux basés sur la technologie bispectrale. L objet de cette thèse est d explorer une nouvelle architecture de PFIR qui intègre dans sa structure même un spectromètre statique par transformée de Fourier. Sur le plan théorique, ce nouveau type de micro-spectromètre présente des atouts particulièrement intéressants pour la mesure à des cadences élevées de spectres infrarouges de faibles niveaux de flux dans un large domaine spectral avec une résolution moyenne, et accepte des sources étendues angulairement. En pratique, deux prototypes ont été réalisés en partenariat avec le CEA-LETI à partir de composants de base de la filière HgCdTe. Ces prototypes ont été caractérisés finement pour comprendre, modéliser et exploiter pleinement les phénomènes d interférence dans la structure de détection. Après avoir établi une méthodologie de mesure, nous avons obtenu des premiers spectres à partir de sources connues. Enfin, les limitations physiques et technologiques ainsi que les perspectives d évolution de ce nouveau concept de microspectromètre seront discutées.Today, important progress in microtechnology allows to produce large format arrays of detectors called infrared focal plane (IRFP), which are integrated in imaging systems. One now studies the possibility of realising spectral imaging systems that would spectrally resolve a scene to extract information from a few bands typically (multispectral imaging). A means of meeting this need is to develop multispectral IRFP. Even if the feasibility of bispectral IRFP was already demontrated in France, it is difficult, even impossible, to consider multispectral IRFP based on bispectral technology. The object of this thesis is to explore a new architecture of IRFP which integrates in its structure a static Fourier transform spectrometer. From the theoretical point of view, this new type of microspectrometer is particularly interesting for high rates measurement of low level, broad band infrared spectra with a medium resolution, and angularly large sources. In practice, two prototypes were realised in partnership with the CEA-LETI, based on classic HgCdTe detectors. These prototypes were characterized to understand, to model and to fully exploit the phenomena of interference in the structure of detection. After having established a methodology of measurement, we obtained first spectra from known sources. Lastly, the physical and technological limitations as well as the prospects for evolution of this new concept of microspectrometer are discussed.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Quantitative experimental characterization of solidpropellant surface temperature before ignition for future model validation

International audienceA general approach is presented in order to estimate the surface temperature and laser power density for solid-propellant ignition studies. It includes an error estimation based on random Monte Carlo draws. The method was demonstrated with a simple phenomenological ignition model adjusted to experimental data obtained with a research AP/HTPB composition. As a first step, only three error sources were considered here. The camera acquisition rate and synchronization are found to have a large impact on the estimated laser power density. A Gaussian laser beam profile was considered to illustrate biases for spatially integrated signals: the apparent ignition happens at the same time as the first local ignition spots, but with shallower temperature slopes. The approach is very promising for the purpose of reducing experimental error levels