Dominique Ausserré

Optimal design for 100% absorption and maximum field enhancement in thin-film multilayers at resonances under total reflection

Dielectric optical coatings are designed at resonances to reach total absorption, whatever the low value of the imaginary index. The corresponding field enhancement within the stack can be arbitrarily increased with the optimization procedure. Applications concern optical sensors and threshold lasers.

Quantitative studies of evanescent wave intensity profiles using optical fluorescence

The fluorescence of uniformly distributed chromophores in an organic solution has been used to probe the energy density profile of an optical evanescent wave, generated by total internal reflection at the solid-solution interface. The results obtained in the case of an aqueous fluorescein solution in contact with a highly polished silica surface are in good quantitative agreement with the expected exponential decay of the optical energy at the interface. It also justifies the use of the newly developed evanescent wave-induced fluorescence technique to study adsorption and depletion layers of polymer in solution close to solids walls. In such experiments the fluorescence intensity is assumed to be the Laplace transform of the concentration profile of the fluorescently labeled polymer chains. The present data validate the above assumption.

Dry Spreading of Polymer Liquids on Solid Surfaces: Role of Long Range Forces, Precursor Film Profiles and Specific Polymeric Effects

We present experimental investigations of the spreading of nonvolatile liquids (polydimethylsiloxane drops) on smooth horizontal silicon wafers. We distinguish the macroscopic part of the drop, which can be seen by bare eye (or through a microscope) from the microscopic part, or precursor film, which progressively develops, like a liquid tongue (thickness smaller than 1000 A) all around the drop. The spreading kinetics of the macroscopic drop appears independent of the spreading parameter, in contrast to the precursor film which is deeply influenced by the surface energies. We have characterized this precursor film (both its profile and its evolution) by optical techniques. The results are compared with the recent de Gennes and Joanny’ theoretical predictions, and specific polymeric effects are pointed out.