Laurent Koechlin's Page at Observatoire Midi Pyrenees 

LK 
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Observatoire Midi Pyrenees, 14 avenue Edouard Belin, 31400 Toulouse, France
Signal, Image & Instrumentation (S2I)
(+33) 5 6133 2887
(+33) 5 6133 2840
reconstruct my email: firstname.lastname@irap.omp.eu
 

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Research activities, projects

I am presently working at Observatoire Midi Pyrénées in a research team : "Signal Image pour les Sciences de l'Univers" (SISU) at  "Institut de Recherches en Astrophysique et Planétologie" (IRAP) , which is a departement of Université de Toulouse associated to CNRS. I also work in collaboration with:

    Observatoire de la côte d'Azur
    Institut d'Astrophysique de PARIS
    Observatoire de Paris
    Universidad complutense de madrid

My main research subject concerns high angular resolution imaging, associated to high dynamic range, aiming to study compact astrophysical objects and their environment, as for example  exoplanets, young exoplanetary systems, circumstellar discs, and the surroundings of AGNs.

I also work for the solar coronagraphic instrumentation at Pic du Midi, with a 4-instrument platform : two 20-cm coronagraphs taking images in H-alpha and HeI lines, and two 9-cm narrow band refractors, taking images of the photosphere in in H-alpha and CaII lines.
See this poster (in French) presenting the subject.
 
My "High dynamic range imaging" work implies developing new instrumental and signal processing concepts. In the recent years, we have developed and tested the Fresnel imager concept, involving an array of specially shaped holes in a thin foil. This foil, dubbed "Fresnel array" is used as a telescope objective, replacing the main mirror.
The optical concept is working in a broad range of wavelengths, from IR to UV. We validate it with a ground-based testbed before proposing it for a space mission. This testbed has a 20 cm square aperture. Due to its long focal length, it is split into two modules, fastened at each end of a long refractor tube.

You can check the most recent results in our paper  :
First high dynamic range and high resolution images of the sky obtained with a diffractive Fresnel array telescope
Published by Expermiental Astronomy : Exp Astron (2012) 33:129–140 DOI 10.1007/s10686-011-9277-7



The Fresnel imager placed on the "grand equatorial". At the far side of the tube, one can see the Fresnel array on its stem. At the near end is placed the receptor module. The beam propagates in free air, outside the tube. The telescope lens is not used.


Images shown below are results of test runs at Nice observatory in 2009 and 2010.
Contributors are: D.Serre, T.Raksasataya, P.Deba, J-P.Rivet, R.Gili, T.Gharsa, J.Platzer, L.Koechlin.


       
Fields on the Moon at first quarter Vallis Alpes (left) and Hipparcos crater (right)                        

 
Satellites of Mars Phobos (left frame) and Deimos (right frame). Theoretical contrasts are 240000 and 680000, respectively relative to Mars, which appears here as a saturated disk. The diagonal spikes are artifacts. As far as we know, we are the first obtain such high contrast images with an aperture as small as 20 cm.
The fact that we use diffractive binary optics rather than a mirror does not mean that classical optics could not do this. However, this proves that lightweight diffractive optics are well suited to high contrast imaging.


Films made on Mars rotation and satellites orbital motion

These films are made with the 20 cm Fresnel array, fastened on the side of the "grand equatorial' at Nice observatory.  Detector used : Andor IXON EMCCD camera.
Each frame of the films is the result of 7x00 short exposure images (0.3s each) piled by "shift and add".
Orientation of axes : E = 108,3°±0.2    ;    N=18.3°±0.2   (origin and sign of angles: trigonometric convention).

The films are "XYT cubes" at .tif format , that can be viewed with ImageJ for example. The images of Mars at center come from the same exposures as the rest of the field, but with a display scale adjusted locally to take into account the large brightness ratio observed between Mars disk and its satellites: 7000 for (pixel-on-Mars / pixel-on-Phobos),
 and 430000 for
(summed-Mars-brightness / summed-Phobos-brightness).

Three films can be retrieved at the following links:
2012-03-03  0h19 to 3h05.   Phobos is below and close to Mars, then goes behind. Towards the end of the film, one can see an occultation by Mars of star TYC 851-421-1, magnitude mv = 10.74.  Deimos is visible too, but at very low S/N ratio, indiquated by a small dash at the first and last frame on which it can be seen.
2012-03-10  Phobos orbits below and around Mars. Bad seeing conditions.
2012-03-11 Phobos orbits below and around Mars. Deimos too, but at very low S/N ratio, indiquated by a small dash at the first and last frame on which it can be seen. Bad seeing conditions.


Other images

 
 Saturn. Both images come from the same data and exp. time, but at different display scales. On the image at right one can see four satellites


Sirius B on the left of Sirius A. Brightness ratio 26000 in the spectral band used : 630-740 nm.

 
Center of Orion Nebula (M42) and sextuple star Theta Orion.
 
Left : narrow band 650-665 nm (H-alpha)                                                           Right: broad band in close IR 745-900 nm.

Presently, we continue developing th econcept, trying to reach TRL4 in the UV domain (Which we already reached in the visible).In collaboration with an interest group, we prepare the science cases for a future space mission, for which we apply for funding.

other online publications

Other research topics