Emiel Por

PhD student at Leiden Observatory

  About me

My name is Emiel Por and I'm a PhD student at Leiden Observatory working on astronomical instrumentation for high contrast imaging under supervision of dr. Matthew Kenworthy. Currently my work is focused on stellar coronagraphy and focal-plane wavefront sensing, more specifically phase sorting interferometry.

My previous work consisted of holographic electric field sensing, under supervision of prof. dr. Christoph Keller, and sparse aperture masking, under supervision of dr. Matthew Kenworthy. Aside from astronomical instrumentation, I did research on post-Newtonian N-body dynamics, supervised by Adrian Hamers MSc. and prof. dr. Simon Portegies Zwart.

  Curriculum Vitae

  Research

Optimal design of apodizing phase plate coronagraphs

Direct observations of exoplanets require a stellar coronagraph to suppress the diffracted starlight. An Apodizing Phase Plate (APP) coronagraph consists of a carefully designed phase-only mask in the pupil plane of the telescope. This mask alters the point spread function in such a way that it contains a dark zone at some off-axis region of interest, while still retaining a high Strehl ratio (and therefore high planet throughput).

Although many methods for designing such a phase mask exist, none of them provide a guarantee of global optimality. Here we present a method based on generalization of the phase-only mask to a complex amplitude mask. Maximizing the Strehl ratio while simultaneously constraining the stellar intensity in the dark zone turns out to be a quadratically constrained linear algorithm, for which a global optimum can be found using large-scale numerical optimizers. This generalized problem yields phase-only solutions. These solutions are therefore also solutions of the original problem.

Using this optimizer we perform parameter studies on the inner and outer working angle, the contrast and the size of the secondary obscuration of the telescope aperture for both one-sided and annular dark zones. We reach Strehl ratios of >65% for a 10−5 contrast from 1.8 to 10 λ/D with a one-sided dark zone for a VLT-like secondary obscuration. This study provides guidelines for designing APPs for more realistic apertures.

  Paper (Por, 2017, Proc. SPIE 10400, Techniques and Instrumentation for Detection of Exoplanets VIII, 104000V)

Major Master Project: Focal-plane electric field sensing with pupil-plane holograms

For direct detection and spectral characterization of exoplanets, a coronagraph is used to suppress the star light. Amplitude and phase aberrations in the optical train fill the dark zone of the coronagraph with quasi-static speckles, limiting the achievable contrast. Focal plane electric field sensing, such as phase diversity introduced by a deformable mirror (DM), provides a powerful tool for correcting this residual star light. Phase probes applied sequentially on the DM inject star light with a well-known amplitude and phase into the dark zone and the resulting intensity images are combined to estimate the residual electric field. The DM can then be used to add light with the same amplitude but opposite phase to destructively interfere with this residual star light.

Using a static phase-only pupil-plane element we create holographic copies of the point spread function (PSF), each superimposed with a certain pupil-plane phase probe. We therefore obtain all intensity images simultaneously, while still retaining a central, unaltered science PSF. The electric field sensing method only makes use of the holographic copies, allowing for correction of the residual electric field while retaining the central PSF for uninterrupted science data collection.

  Paper (Por & Keller, 2016, Proc. SPIE 9909, Adaptive Optics Systems V, 990959)

  Poster

  Closed loop movie with rotating static speckle background

Minor Master Project: Post-Newtonian N-body Dynamics

The majority of codes for relativistic N-body simulations fail to take all known first post-Newtonian order terms in the equations of motion into account for computational reasons. Will (2014) showed that in some cases, for instance hierarchical systems or systems with a central massive object, some of the neglected terms are of similar or even higher importance than the terms that are taken into account, and he provides a way to efficiently calculate the relevant neglected terms, called cross-terms. We evaluate his method and provide expressions for the cross-terms in the case of multiple massive objects, yielding terms of similar algorithmic complexity.

We use the Hermite integration scheme and Kustaanheimo-Stiefel regularization in the quaternion formation to numerically integrate the full first post-Newtonian equations of motion, in order to investigate the importance of the neglected terms. The code was validated using both two-body and hierarchical triple systems, reproducing the osculating elements derived analytically using Lagranges planetary equations, and the resonant eccentricity excitations, induced by post-Newtonian effects, recently obtained using purely secular orbital averaging methods by Naoz (2013). We however failed to reproduce their results for eccentric Kozai mechanism induced purely by post-Newtonian effects, instead of the usual Newtonian octupole variations, casting doubt on the existance of such a mechanism.

  Thesis

Bachelor Project: Sparse Aperture Masking at the Leiden Old Observatory

We designed and implemented a Michelson interferometry observing mode called Sparse Aperture Masking (SAM) or Non-Redundant Masking (NRM) at optical wavelengths on the student telescope located in the Westkoepel in the Leiden Old Observatory. The telescope was transformed into a seven-element interferometer using an aperture mask located in front of the primary mirror. Methods for designing this mask are discussed. A data-reduction pipeline was written in Python and the whole setup was validated using first-light observations of a 3 magnitude contrast binary at 1.5 λ/D separation. Algorithms for creating Kolmogorov phase screens involved in simulations are also discussed.

  Thesis

 Teaching

Astronomical Observing Techniques (2014, 2016, 2017, 2018, 2019)

I was teaching assistant (TA) for Astronomical Observing Techniques, taught by Christoph Keller in Autumn 2014, Spring 2016, Spring 2017 and Spring 2018, and by Huub Rottgering in Spring 2019. This second/third-year Bachelor course provides students with a general overview of both the underlying physical principles and the technical concepts of the technologies and equipment being used in observational astronomy.

  Course website

Natuurkunde B (2013)

I was teaching assistant for Natuurkunde B, taught by Martina Huber in Autumn 2013. This second-year Bachelor course for Life Science and Technology students provides a basic understanding of the principles of quantum mechanics in physical chemistry covering, among other things, atomic structure, biatomic molecules and valence bonds.

  Contact Information

Email

por [at] strw.leidenuniv.nl

Office

Oort Building
Niels Bohrweg 2
2333 CA Leiden
Room 1105

Curriculum Vitae

  CV