Frédéric Celle

Wide band, wide angular width wire-grid polarizer using galvanic growth technology

Functional demonstration of a wide band, wide angular width “wire-grid polarizer” has been made in the framework of a User Project of the European project ACTMOST (Access To Micro-Optics Expertise, Services and Technologies). The polarization function relies upon linear polarizers using the “wire-grid” polarizer principle by means of a metal grating of unusually large period, exhibiting a large extinction of the transmission of the TE polarization in the 850 nm wavelength range. This grating achieves a broadband and especially high angular aperture reflection with low loss and permits resorting to very low cost incoherent light sources of the transmitted TM polarization. The paper will describe the design, the modeling optimization, and the complete technological process chain which has been used: from the photoresist grating printing using phasemask UV-based lithography to the uniform galvanic growth of very shallow gold grating on transparent conductive layer deposited on a glass substrate. Transmission curves for both polarizations on the first demonstrators will be presented.

Surface temperature measurement through surface plasmon resonance

The aim of this work is to highlight the possibility of local non-intrusive temperature measurements at the interface between a metallic surface and a fluid by analyzing the plasmon resonance on a periodically micro-structured surface. A change in the temperature of the sample surface induces a modification of the local refractive index leading to a shift of the surface plasmon resonance frequency due to interactions between the evanescent electric field and the close environment of the surface. The metallic gratings developed in this study enable a direct excitation of a plasmonic wave, which, in turn, lead to a high sensibility of the local temperature measurement with a very compact and simple device.

Condensation phenomenon detection through surface plasmon resonance

The aim of this work is to optically detect the condensation of acetone vapor on an aluminum plate cooled down in a two-phase environment (liquid/vapor). Sub-micron period aluminum based diffraction gratings with appropriate properties, exhibiting a highly sensitive plasmonic response, were successfully used for condensation experiments. A shift in the plasmonic wavelength resonance has been measured when acetone condensation on the aluminum surface takes place due to a change of the surrounding medium close to the surface, demonstrating that the surface modification occurs at the very beginning of the condensation phenomenon. This paper presents important steps in comprehending the incipience of condensate droplet and frost nucleation (since both mechanisms are similar) and thus to control the phenomenon by using an optimized engineered surface.

Improvement of solar absorption using submicrometric gratings

The paper demonstrates a rigorous modeling approach for 1D microstructured absorbing multi-layers for the receivers of CSP (Concentrated Solar Power), taking into account both absorption of the incident solar energy and the emissivity while considering receivers temperature. From an optimized multilayers structure achieving high absorption, the authors demonstrate that 1D sub wavelength period gratings could increase further the absorption and thus the yield of the Concentrated Solar Power system. The authors used C-method (Chandezon Method) to optimize 1D grating profile. Experimental demonstration on Silicon wafers combining writing grating and absorptive layers deposition are also presented. Experimental results are presented and absorbance enhancement of almost 2% are achieved with values of 96.5% in the visible and UV range. The results are promising for the design of future and competitive solar absorbers for CSP since the microstructuring fabrication approach can be applied to non-planar substrates such as tubes, which are the receivers of the CSP.