Multifunctional optical Windows : Antireflective and Superhydrophobic – F-MARS

The F-MARS project aims to design and fabricate multifunctional optical windows (antireflective and superhydrophobic) based on the outstanding properties of nanostructured surfaces.

This research project is motivated by the very promising results obtained in the framework of the Thales/DGA PhD thesis of Timothée Mouterde and of previous TRT studies. In these works, the influence of the size and shape of micro-nano structures on superhydrophobic surfaces behaviors has been studied using reference surfaces. These studies have highlighted the large diversity of fluidic properties (anti-rain, anti-mist) exhibited by such surfaces, as a function of feature sizes. They have also demonstrated the possibility to achieve the combination of superhydrophobic properties with high-performance antireflective properties (wideband, high incidence angle), thanks to the use of conical shaped-nanostructures. Hence this work opens a new path for the realization of high performance multifunctional optical windows. Those windows aim to answer the needs of many optical systems used in civil and military fields: terrestrial and maritime panoramic surveillance systems, visible and infrared cameras, windows used in space instrumentation, … There is today a gap between the very sophisticated technologies used in these systems and the solutions adressing the issue of humidity. This project intends to close this gap by simplifying the design of these systems (removal of wipers and regeneration systems, …) while increasing their performances (better optical yield, increased time of operation, regardless environmental conditions).

In addition to multifunctionality, the originality of this technology lies in the fact that micro/nano roughness is not derived from a coating method, as the solutions currently available on the market, but results from the structuration of the bulk material constituting the optical windows. The work of the Consortium made up of two academic partners (PMMH (Laboratoire de Physique et Mécanique des Milieux Hétérogène, ESPCI) and LMS (Laboratoire de Mécanique des Solides, Ecole Polytechnique)) and an industrial one (Thales TRT), will focus both on fundamental studies (understanding physics at the nanoscale) and on the development of pre-industrial nanopatterning processes.
Taking into consideration the state of art, challenges of F-MARS project are as follows:
(1) Develop large-scale processes (3-inch windows), for the nanostructuration of materials addressing the visible range (glass) and the infrared range (silicon and germanium). The nanoimprint technology is the industrial solution that has been chosen to achieve this objective.
(2) Characterize and improve the mechanical robustness of these nanostructured surfaces. The nature of our approach, based on materials structuration, answers this objective. An additional line is also addressed in the project and will concern the covering of nanostructures by a thin layer whose hardness is similar to that of sapphire or diamond.
(3) Determine, by simulations and experiments, the structure geometry allowing to obtain simultaneously antireflective properties, robustness, and superhydrophobic behaviors (anti-rain, anti-mist, self-cleaning) for three spectral bands (visible, mid-wave infrared and long-wave infrared). A parametric study of these properties will be performed in order to obtain the geometry offering the best compromise.

All of these studies will lead to the demonstration of multifunctional large-scale optical windows with technologies that are applicable to optical systems products of French industry.