Lionel Clermont

Spectral splitting planar solar concentrator: experimental testing of a design aiming at dye sensitized solar cells

We present a new solar concentrator concept. This concept is based on spectral splitting. It implies reflective, refractive and diffractive elements that allow two spectrally differentiated beams to reach different and/or unmatched lattice solar cells. The aimed geometrical concentration factor is 5× and the theoretical optical efficiency of that concentrator concept reaches theoretically 82%. The following study will discuss the concept of such a solar concentrator. A practical application to dye sensitized solar cells is given. The manufacturing and design of the element is then exposed. Those elements have been tested in the laboratory. Good agreements with theoretical simulations are demonstrated.

Alignment and calibration of the ICON-FUV instrument: Development of a vacuum UV facility

The optical calibration of the ICON-FUV instrument requires designing specific ground support equipment (GSE). The ICON-FUV instrument is a spectrographic imager that operates on two specific wavelengths in the UV (135.6 nm and 157 nm). All the operations have to be performed under vacuum UV light. The optical setup is based on a VUV monochromator coupled with a collimator that illuminates the FUV entrance slit. The instrument is placed on a manipulator providing fields pointing. Image quality and spectral properties can be then characterized for each field. OGSE, MGSE, optical calibration plan and vacuum alignment of the instrument are described.

Automatized alignment of the focal plane assemblies on the PLATO cameras

PLATO (PLAnetary Transits and Oscillation of stars) is a medium-class space mission part of the ESA Cosmic vision program. Its goal is to find and study extrasolar planetary systems, emphasizing on planets located in habitable zone around solar-like stars. PLATO is equipped with 26 cameras, operating between 500 and 1000nm. The alignment of the focal plane assembly (FPA) with the optical assembly is a time consuming process, to be performed for each of the 26 cameras. An automatized method has been developed to fasten this process. The principle of the alignment is to illuminate the camera with a collimated beam and to vary the position of the FPA to search for the position which minimizes the RMS spot diameter. To reduce the total number of measurements which is performed, the alignment method is done by iteratively searching for the best focus, decreasing at each step the error on the estimated best focus by a factor 2. Because the spot size at focus is similar to the pixel, it would not be possible with this process alone to reach an alignment accuracy of less than several tens of microns. Dithering, achieved by in-plane translation of the focal plane and image recombination, is thus used to increase the sampling of the spot and decrease the error on the merit function.

Stray-light calibration and correction for the MetOp-SG 3MI mission

The MetOp-SG 3MI mission is part of the EUMETSAT Polar System Second Generation (EPS-SG), an Earth observation Program for Operational Meteorology from Low Earth Orbit. It consists of two multi-spectral cameras, one operating in VNIR and one in SWIR. With 13 spectral channels between 410nm and 2130nm, including polarized channels, the instrument covers a semi-field of view of 57°. Due to tight stray-light specifications, on-ground calibration and post-processing correction are required. This paper covers the stray-light correction and calibration methods. The correction is indeed based on the on-ground measurement of Spatial Point Source Transmittance (SPST) maps. Due to the limited amount of maps which can actually be calibrated within a reasonable amount of time, an interpolation method was developed to deduce the stray-light behavior in the whole field of view of the instrument. Furthermore, dynamic range decomposition was required during the acquisition of the maps to get a high signal to noise ratio. Ray-tracing data from the 3MI optical model were used to evaluate the performance of the correction algorithm, including the contribution of SPST maps interpolation and acquisition errors.

Comparison of off-axis TMA and FMA telescopes optimized over different fields of view: applications to Earth observation

TMA, or three mirror anastigmats, have already been used successfully for various space missions. In the frame of earth observation, ProbaV satellite uses 3 TMAs to cover a total 102.4° field-of-view; ground sampling distance is about 100m at the center of field-of view and 370m at the edge. For future earth observation missions, the goal would be to reach 100m spatial resolution all over the 102.4° FOV. This would require to up-scale optical specifications, thus increasing geometrical aberrations. FMA, or four mirror anastigmats, could thus be a good candidate for future missions, as a fourth mirror would allow better correction of optical aberrations. In this work, TMA and FMA have been optimized over different fields-of view. Performance limitations are then derived, which show that FMA seems promising for future missions. Radiometry aspects are discussed and preliminary tolerance analysis is carried out.

Spectral splitting planar solar concentrator : Design and Experimental testing Preliminary results

We present a new solar concentrator concept. This concept is based on spectral splitting. It implies reflective, refractive and diffractive elements that allow two spectrally differentiated beams to reach different and/or unmatched lattice solar cells. The aimed geometrical concentration factor is 5× and the theoretical optical efficiency of that concentrator concept reaches theoretically 82%. The following study will discuss the concept of such a solar concentrator. A practical application to dye sensitized solar cells is given. The manufacturing and design of the element is then exposed. Those elements have been tested in the laboratory. Good agreements with theoretical simulations are demonstrated.