A5068770249- Adaptive optics and wavefront sensing
- Optical Systems and Laser Technology
- Advanced optical system design
- Stellar, planetary, and galactic studies
- Optical Wireless Communication Technologies
- Astronomy and Astrophysical Research
- Optical measurement and interference techniques
- Optical Coherence Tomography Applications
- Atmospheric aerosols and clouds
- Optical Coatings and Gratings
- Advanced Optical Sensing Technologies
- Plant Water Relations and Carbon Dynamics
- Calibration and Measurement Techniques
- Atmospheric Ozone and Climate
- Meteorological Phenomena and Simulations
- Solar Radiation and Photovoltaics
- Photorefractive and Nonlinear Optics
- Atmospheric chemistry and aerosols
- Astronomical Observations and Instrumentation
- Satellite Image Processing and Photogrammetry
- Advanced X-ray Imaging Techniques
- Surface Roughness and Optical Measurements
- Atmospheric and Environmental Gas Dynamics
- Laser Material Processing Techniques
- Fluid Dynamics and Turbulent Flows
Durham University
2015-2024
Leiden Observatory
2020
University of Arizona
2020
Leiden University
2020
University of New Hampshire
2020
University of Reading
2008-2009
Pacific Northwest National Laboratory
2009
University of Washington
2009
Rutgers, The State University of New Jersey
2009
Goddard Institute for Space Studies
2009
The African Monsoon Multidisciplinary Analysis (AMMA) is a major international campaign investigating far‐reaching aspects of the monsoon, climate and hydrological cycle. A special observing period was established for dry season (SOP0) with focus on aerosol radiation measurements. SOP0 took place during January February 2006 involved several ground‐based measurement sites across west Africa. These were augmented by aircraft measurements made Facility Airborne Atmospheric Measurements (FAAM)...
Context. The wind-driven halo is a feature that observed in images were delivered by the latest generation of ground-based instruments are equipped with an extreme adaptive optics system and coronagraphic device, such as SPHERE at Very Large Telescope (VLT). This signature appears when atmospheric turbulence conditions vary faster than loop can correct for. radial extension point spread function along distinct direction (this sometimes referred to butterfly pattern). When this present, it...
Recent advances in adaptive optics (AO) have led to the implementation of wide field-of-view AO systems. A number wide-field systems are also planned for forthcoming Extremely Large Telescopes. Such multiple wavefront sensors different types, and usually deformable mirrors (DMs). Here, we report on our experience integrating cameras DMs with real-time control two These CANARY, which has been operating on-sky since 2010, DRAGON, is a laboratory demonstrator instrument. We detail issues...
An overview is presented of the meteorological and thermodynamic data obtained during Radiative Atmospheric Divergence using Radiation Measurement (ARM) Mobile Facility, Geostationary Earth Budget (GERB) data, African Monsoon Multidisciplinary Analysis (AMMA) stations (RADAGAST) experiment in Niamey, Niger, 2006. RADAGAST combined from ARM Program Facility (AMF) at Niamey airport with broadband satellite GERB instrument on Meteosat‐8. The was conducted collaboration AMMA project. focus this...
The latest generation of high contrast instruments dedicated to exoplanets and circumstellar disks imaging are equipped with extreme adaptive optics coronagraphs reach contrasts up 10^--4 at a few tenths arc-seconds in the near infrared. resulting image shows faint features, only revealed this combination, such as wind driven halo. halo is due lag between correction turbulence speed over telescope pupil. However we observe an asymmetry that was not expected when instrument designed. In...
Broadband shortwave and longwave radiative fluxes observed both at the surface from space during Radiative Atmospheric Divergence using ARM Mobile Facility, GERB data AMMA Stations (RADAGAST) experiment in Niamey, Niger, 2006 are presented. The were measured by Radiation Measurement (ARM) Program Facility (AMF) Niamey airport, while top of atmosphere (TOA) Geostationary Earth Budget (GERB) instrument on Meteosat‐8 satellite. analyzed as daily averages, order to minimize sampling differences...
A deformable mirror (DM) is a whose surface can be deformed in order to correct for optical aberrations. If DM used feed-forward operation (i.e. without feed-back, also known as open-loop) it is, among other requirements, crucial that set of actuator commands repeatedly results the same shape. We have tested an ALPAO against this criterion, by applying over hours and monitoring shape with interferometer. found if was held several hours, then changed second shape, ℬ, will drift from new...
ABSTRACT Dedicated tip–tilt loops are commonly implemented on adaptive optics (AO) systems. In addition, a number of recent high-performance systems feature controllers that more efficient than the integral action controller. this context, linear–quadratic–Gaussian (LQG) regulators based stochastic models identified from AO telemetry have demonstrated their capacity to effectively compensate for cumulated effects atmospheric disturbance, windshake and vibrations. These LQG can also be...
Direct imaging instruments have the spatial resolution to resolve exoplanets from their host star. This enables direct characterization of atmosphere, but most do not spectrographs with high enough resolving power for detailed atmospheric characterization. We investigate use a single-mode diffraction-limited integral-field unit that is compact and easy integrate into current future exoplanet achieved by making recent progress in photonic manufacturing create fiber-fed image reformatter. The...
CuReD (Cumulative Reconstructor with domain Decomposition) and HWR (Hierarchical Wavefront Reconstructor) are novel wavefront reconstruction algorithms for the Shack–Hartmann sensor, used in single-conjugate adaptive optics. For a high-order system they much faster than traditional matrix–vector-multiplication method. We have developed three methods mapping reconstructed phase into deformable mirror actuator commands tested both reconstructors CANARY instrument. find out that reconstructor...
CANARY is an on-sky Laser Guide Star (LGS) tomographic AO demonstrator that has been in operation at the 4.2m William Herschel Telescope (WHT) La Palma since 2010. In 2013, was upgraded from its initial configuration used three off-axis Natural Stars (NGS) through inclusion of four Rayleigh LGS and associated wavefront sensing system. Here we present system analysis results obtained WHT between May September 2014. Finally final 'Phase C' aims to recreate emulate expected both AOF VLT E-ELT.
We present the first on-sky results of a four-telescope integrated optics discrete beam combiner (DBC) tested at 4.2 m William Herschel Telescope. The device consists four-input pupil remapper followed by DBC and 23-output reformatter. whole was written monolithically in single alumino-borosilicate substrate using ultrafast laser inscription. operated astronomical H-band (1.6 µm), deformable mirror along with microlens array used to inject stellar photons into device. report measured...
In the Radiative Atmospheric Divergence Using ARM Mobile Facility GERB and AMMA Stations (RADAGAST) project we calculate divergence of radiative flux across atmosphere by comparing fluxes measured at each end an atmospheric column above Niamey, in African Sahel region. The combination broadband measurements from geostationary orbit deployment for over 12 months a comprehensive suite active passive instrumentation surface eliminates number sampling issues that could otherwise affect...
Simultaneous observations of thermal radiative fluxes and radiances from the surface (Atmospheric Radiation Measurement Mobile Facility, Niamey) top atmosphere (Geostationary Earth Budget (GERB) instrument) during Radiative Atmospheric Divergence using ARM GERB data, AMMA Stations experiment are compared with results a transfer model (Edwards‐Slingo). Emphasis is placed on diagnosing accuracy cloud‐free radiation measurements multiple instruments at surface. The forcing aerosol found to...
We have analysed and simulated a novel alternative Laser Guide Star (LGS) configuration termed Projected Pupil Plane Pattern (PPPP), including wavefront sensing the reconstruction method. A key advantage of this method is that collimated beam launched through telescope primary mirror, therefore measurements do not suffer from effects focal anisoplanatism. detailed simulation upward wave optics propagation, return path imaging, linearized has been presented. The conclusions we draw include...
The spatial description of aberrations produced by atmospheric turbulence for astronomical applications is agreed to be well modeled the Kolmogorov theory energy cascades. Instances these can easily generated using closed-form analytic models based on power-spectra following von Karman model. However, in it also temporal evolution which interest. this aspect less established, and generally assumed follow Taylor Hypothesis over large time-scales as an approximation. This described follows: if...
We present a wavefront sensor design for the purpose of measuring post-AO corrected light, especially in cases high-Strehl and when using natural guide stars. It is inspired by holographic principles oers approximately two orders magnitude increase sensitivity over conventional Shack-Hartmann design. The theoretical that laboratory prototype are presented, together with simulation results case-study sinusoidal phase corresponding from experiment.
DRAGON is a real-time, tomographic Adaptive Optics test bench currently under development at Durham University. Optical and mechanical design work for now complete, the system close to becoming fully operational. emulates current 4.2 m 8 telescopes, can also be used investigate ELT scale issues. The full features 4 Laser Guide Star (LGS) Wavefront Sensors (WFS), 3 Natural (NGS) WFSs one Truth Sensor, all of which are 31 × sub-aperture Shack-Hartmann WFS. Two Deformable Mirrors (DMs), Boston...
The direct detection and imaging of exoplanets requires the use high-contrast adaptive optics (AO).In these systems quasi-static aberrations need to be highly corrected calibrated.In order achieve this, a high-sensitivity wavefront sensor, pupil-modulated point-diffraction interferometer (m-PDI), is presented.This sensor modulates retrieves both phase amplitude an incoming electric field.The theory behind reconstruction, visibility fringes, chromatic effects noise propagation are...
Laser Guide Stars (LGS) have greatly increased the sky-coverage of Adaptive Optics (AO) systems. Due to up-link turbulence experienced by LGSs, a Natural Star (NGS) is still required, preventing full sky-coverage. We present method obtaining partial tip-tilt information from LGSs alone in multi-LGS tomographic LGS AO The determination derived using geometric approach, then an alteration Learn and Apply algorithm for made accommodate tip-tilt. Simulation results are presented, verifying that...
DRAGON is be a new and in many ways unique visible light adaptive optics test bench. Initially, it will existing concepts for CANARY, the laser guide star tomographic demonstrator on WHT, then later used to explore other future telescopes. Natural Laser Guide Stars (NGS LGS) are emulated, where LGSs exhibit effects of passing up through turbulence spot elongation. AO correction performed by one high low order deformable mirror, allowing woofer-tweeter control, multiple wave front sensors...
The Multi-Core Integral-Field Unit (MCIFU) is a new diffraction-limited near-infrared integral-field unit for exoplanet atmosphere characterization with extreme adaptive optics (xAO) instruments. It has been developed as an experimental pathfinder spectroscopic upgrades SPHERE+/VLT and other xAO systems. wavelength range covers 1.0 um to 1.6um at resolving power around 5000 73 points on-sky. MCIFU uses novel astrophotonic components make this very compact robust spectrograph. We performed...