2 August 2014 Shaping the PSF to nearly top-hat profile: CHEOPS laboratory results
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Abstract
Spreading the PSF over a quite large amount of pixels is an increasingly used observing technique in order to reach extremely precise photometry, such as in the case of exoplanets searching and characterization via transits observations. A PSF top-hat profile helps to minimize the errors contribution due to the uncertainty on the knowledge of the detector flat field. This work has been carried out during the recent design study in the framework of the ESA small mission CHEOPS. Because of lack of perfect flat-fielding information, in the CHEOPS optics it is required to spread the light of a source into a well defined angular area, in a manner as uniform as possible. Furthermore this should be accomplished still retaining the features of a true focal plane onto the detector. In this way, for instance, the angular displacement on the focal plane is fully retained and in case of several stars in a field these look as separated as their distance is larger than the spreading size. An obvious way is to apply a defocus, while the presence of an intermediate pupil plane in the Back End Optics makes attractive to introduce here an optical device that is able to spread the light in a well defined manner, still retaining the direction of the chief ray hitting it. This can be accomplished through an holographic diffuser or through a lenslet array. Both techniques implement the concept of segmenting the pupil into several sub-zones where light is spread to a well defined angle. We present experimental results on how to deliver such PSF profile by mean of holographic diffuser and lenslet array. Both the devices are located in an intermediate pupil plane of a properly scaled laboratory setup mimicking the CHEOPS optical design configuration.
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Demetrio Magrin, Demetrio Magrin, Jacopo Farinato, Jacopo Farinato, Gabriele Umbriaco, Gabriele Umbriaco, Kalyan Kumar Radhakrishnan Santhakumari, Kalyan Kumar Radhakrishnan Santhakumari, Maria Bergomi, Maria Bergomi, Marco Dima, Marco Dima, Davide Greggio, Davide Greggio, Luca Marafatto, Luca Marafatto, Roberto Ragazzoni, Roberto Ragazzoni, Valentina Viotto, Valentina Viotto, Matteo Munari, Matteo Munari, Isabella Pagano, Isabella Pagano, Gaetano Scandariato, Gaetano Scandariato, Salvatore Scuderi, Salvatore Scuderi, Giampaolo Piotto, Giampaolo Piotto, Thomas Beck, Thomas Beck, Willy Benz, Willy Benz, Christopher Broeg, Christopher Broeg, Virginie Cessa, Virginie Cessa, Andrea Fortier, Andrea Fortier, Daniele Piazza, Daniele Piazza, } "Shaping the PSF to nearly top-hat profile: CHEOPS laboratory results", Proc. SPIE 9143, Space Telescopes and Instrumentation 2014: Optical, Infrared, and Millimeter Wave, 91434L (2 August 2014); doi: 10.1117/12.2055858; https://doi.org/10.1117/12.2055858
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