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16 mars 2018 Tout le mois


Frans Snik (Leiden) - HIGH-CONTRAST IMAGING WITH LIQUID CRYSTALS

Vendredi 16 mars 11:00-12:00

To directly image and characterize exoplanets, we need advanced optical
systems on current Very Large and future Extremely Large telescopes that
can suppress the bright glare of stars by 6-10 orders of magnitude, and
analyze the feeble light of potential planetary companions. Such
high-contrast imaging systems consist of advanced adaptive optics and
associated wavefront sensing techniques, coronagraphy to (locally)
suppress the diffracted starlight, contrast-enhancing techniques like
angular/spectral/polarimetric differential imaging, and diagnostic
capabilities like (high-resolution) spectroscopy and
(spectro)polarimetry. In our group in Leiden we cover all these
different aspects of high-contrast imaging, with the aim to achieve the
ultimate contrast performance and characterization potential with a
complete, integrated end-to-end system for ground-based telescopes. We
are currently exploiting brand-new liquid-crystal technologies that
offer important performance benefits for many components in a
high-contrast imaging instrument, and for the system as a whole. We have
introduced the “vector-APP” coronagraph that has currently been
successfully commissioned at MagAO, LBT, and SCExAO, and are developing
versions for several other telescopes and instruments, including a
stratospheric balloon telescope. We apply lessons learnt from the
vector-APP to the Vector Vortex Coronagraph to enhance its spectral
range and suppression. Novel versions of the vector-APP now have several
methods for focal-plane wavefront sensing built in, and we are currently
also testing versions of Pyramid and Zernike wavefront sensors with
enhanced performance thanks to liquid-crystal implementations. As
vector-APP coronagraphs are broadband, we are applying them for
integral-field spectroscopy, and developing versions that are optimally
matched to fiber-fed spectrographs. And as the vector-APP is based on
polarization tricks, we are extending it with polarimetric
implementations. We are currently even playing with crazy
liquid-crystal-based Sparse Aperture Masking concepts that are heavily
multiplexed, and can include achromatic nulling. I will provide an
overview of these projects, and an outlook for implementing such
techniques at the VLT and the ELT to ultimately characterize rocky
planets in the habitable zones of nearby stars.

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