Hi all,

This week, we have Jules Fowler visiting. They got a guest office in 3.22. Please swing by if you are interested in having a chat about AO or exoplanet polarimetry. Jules will also give a talk (see title and abstract below) at the group meeting this week at 11:00 – 12:00 on Wednesday September 3rd! We meet in the Oort room.

Standard rules apply to the meetings again. You need to send in 2 slides with at least one figure per slide. Unless you have a PhD, then you are exempt from sending in slides (they are still appreciated!).

We will also have a group social / dinner tomorrow evening at 18:00 at Oudt Leyden. If you want to come, please let me know. I think most people have already RSVP’d.

Other news, Louis Desdoigt started his postdoc with me today! His office is 3.46BW. I will make sure he will give a talk about his past work somewhere in the next weeks =).

Title: Predictive wavefront control in theory, on testbed, and on-sky: using predictive wavefront control to tackle temporal errors and improve ground-based high contrast imaging

Abstract: From the ground, the direct imaging of exoplanets requires extreme adaptive optics (XAO), where the adaptive optics correction is optimized over a small field-of-view. With major development in wavefront sensor and deformable mirror technology in recent years, temporal error remains as one of the leading error terms in many AO and XAO systems. While most AO systems operate at 0.1-2 kHz timescales, Earth-atmosphere moves faster. Atmospheric turbulence is driven by wind layers that blow an AO correction into history before it can be applied, causing wavefront errors on spatial scales that lead to speckles at small angular separations from the host star in the final science image. One avenue for correcting these aberrations is predictive wavefront control, wherein previous wavefront information is used to predict the future state of the wavefront in one-system-lag's time, and this predicted state is applied as a correction. Predictive control not only reduces speckle noise in standard observations, but also opens up the sky to targets that would otherwise be too faint to be natural guidestars. Additionally, predictive control requires no hardware changes (e.g., new equipment or optical redesign) – it can be implemented only with software changes. While predictive methods have been in the literature for more than 40 years in a handful of different flavors, there has yet to be (1) a side-by-side comparison of different predictive methods or (2) a facilitized implementation on-sky. In this talk I will address both; I present a comparison of data-driven (Empirical Orthogonal Functions, EOF) and model-driven (Predictive Fourier Control) predictive control algorithms, and work to compare them in simulation and on the Santa Cruz Extreme AO Lab testbed. I will also discuss on-sky experiments running EOF at Keck Observatory and recent work to implement EOF into the new Keck-II RTC. Work on predictive methods not only improves current observing at highly productive 8-10 meter class telescopes, but acts as a pathfinder for ELTs.

Met vriendelijke groet / With kind regards,

Dr. Sebastiaan Haffert

Assistant professor

Leiden Observatory, Leiden University

Einsteinweg 55, 2333 CC, Leiden, The Netherlands