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In the context of high-contrast imaging, dual-polarization wavefront sensing represents
a very promising solution for non-common path aberrations and aberrations control using
the vortex coronagraph. The interest of this method lies in the efficient phase retrieval
using the unique polarization behaviour of the vortex coronagraph and the simplicity of
its implementation. This method has been progressively implemented on Vortex Optical
Demsontrator for Coronagraphic Application (VODCA) test bench using the vortex coronagraph
called the Annular Groove Phase Mask (AGPM).
The dual-polarization setup requires the most accurate selection of both orthogonal circular
polarizations before and after the focal plane. An accurate polarization setup is
optimized to ensure the purest circular polarization for both orthogonal states at more
than 97% at the focal plane on VODCA. In order to achieve this level of precision, two
polarization measurement methods have been presented. The classical method and the
rotating quarter wave plate (QWP) method. Both are used and compared to characterize
how the polarization state of the light was impacted by the optical elements of VODCA.
The rotating QWP method is used to optimize the accuracy of the circular polarizer being
more precise and consistent than the classical method.
With the optimized circular polarizer, the dual polarization setup has been evaluated in
terms of two particular performance values, the extinction ratio and the rejection ratio. The
setup has achieved a non-expected high performance comparable to particularly efficient results
obtained in previous studies. Considering the polarization setup without the AGPM,
an extinction ratio of 1924 has been achieved. Due to intrinsic performance of the AGPM,
the setup with the vortex coronagraph has achieved an extinction ratio of 1521. Moreover,
a rejection ratio of 2010 has been obtained for the AGPM. This result has been obtained
using a aberration minimization routine to avoid limiting performance due to aberrations
in the focal plane. The total contrast achieved by the dual-polarization setup is up to 21e4.
These performance ensured a sufficiently high accuracy of the setup to produce a required
diversity for phase retrieval. This produced diversity has been proven by using the deformable
mirror (DM) of VODCA to inject specific aberrations in the focal plane and
verify the lifting of the sign ambiguity which was confirmed. Following this, some CNN
training on aberration identification have led to relative successful wavefront reconstruction
tests performed using machine learning.
The dual-polarization setup developed in this work combined with the polarization behaviour
of the phase mask allows a sufficient diversity to ensure a performing phase retrieval.
However, these results are still preliminary in sight of a laboratory validation of the
dual-polarization wavefront sensing using the vortex coronagraph.

Ingénierie, informatique & technologie > Ingénierie aérospatiale

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Astronomical images are often degraded by the disturbance of the Earth’s atmosphere. This thesis proposes to improve image-based wavefront sensing techniques using machine learning algorithms. Deep convolutional neural networks (CNN) have thus been trained to estimate the wavefront using one or multiple intensity measurements.

Ingénierie, informatique & technologie > Sciences informatiques

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When lensed AGNs are discovered, the primary focus is usually on their lensing properties
rather than their physical properties. This Master thesis aims at finding new estimates of the
physical properties of a sample of ten gravitationally lensed quasars using a uniform method based on spectral modelling and scaling relations. The sample is comprised of doubly and quadruply lensed quasars at redshifts roughly between 1.5 and 2.6 showing various spectral properties. The physical properties computed here are the black hole mass, the Eddington ratio and the size of the BLR. The latter allows an estimation of the sensitivity of the source to the microlensing effect assuming a theoretical lens mass. 
The basis on which the determination of the physical properties rests is the optical/UV
spectra obtained from various instruments such as the MUSE (Multi-Unit Spectroscopic Explorer)
or the FORS (FOcal Reducer and low dispersion Spectrograph) instruments of the VLT. The
methodology can be summarized as follows. The first step is the modelling of the considered
spectrum and the identification of known broad and narrow emission lines. Secondly, the black
hole mass estimate and the size of the BLR are computed using known scaling relations based
on the virial theorem. These involve the calibrated intrinsic luminosity of the continuum either
at 1450 or 3000 Å depending on the chosen emission line, either C IV at 1549Å or Mg II at 2798
Å. Finally, the accretion efficiency is evaluated by the ratio between the Eddington luminosity,
which is the upper limit on the luminosity an AGN can theoretically have, and the bolometric
luminosity. The sensitivity to the microlensing effect is then evaluated by the ratio of the size of
the Broad Line Region to the projected Einstein radius of the microlens. The uncertainties of each of the physical quantity are also computed. Finally, a discussion about the implications of this method and its limitation is given.

Physique, chimie, mathématiques & sciences de la terre > Aérospatiale, astronomie & astrophysique

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The quasar system 2M1134-2103 is analysed using ESO-MUSE integral field spectrograph. 2M1134-2103 is a quadruple lensed quasar and the dynamics of such a system are intriguing to study. Several properties have been studied and derived for the system but first, data reduction process of the MUSE pipeline is analysed and a sysnthesis is made for a future user. Next, the goal is to derive information about the system, so for that purpose a code is written in this work to extract the spectrum of the lensing galaxy as well as the spectra of the lensed quasar images. The redshift of the lensing galaxy was unknown at the beginning of this thesis and its estimated in this work, along with the redshift of the quasar and some galaxies in the FOV. The corresponding emissions and absorptions in the lensing galaxy and the quasar are studied and presented. The black hole mass of the system is also derived using scaling relations and the spectra of the quasar are analysed for microlensing using the MmD technique.

Physique, chimie, mathématiques & sciences de la terre > Aérospatiale, astronomie & astrophysique