Richard M. Myers

MOAO first on-sky demonstration with CANARY

Context. A new challenging adaptive optics (AO) system, called multi-object adaptive optics (MOAO), has been successfully demonstrated on-sky for the first time at the 4.2 m William Herschel Telescope, Canary Islands, Spain, at the end of September 2010. Aims. This system, called CANARY, is aimed at demonstrating the feasibility of MOAO in preparation of a future multi-object near infra-red (IR) integral field unit spectrograph to equip extremely large telescopes for analysing the morphology and dynamics of high-z galaxies. Methods. CANARY compensates for the atmospheric turbulence with a deformable mirror driven in open-loop and controlled through a tomographic reconstruction by three widely separated off-axis natural guide star (NGS) wavefront sensors, which are in open loop too. We compared the performance of conventional closed-loop AO, MOAO, and ground-layer adaptive optics (GLAO) by analysing both IR images and simultaneous wave-front measurements. Results. In H-band, Strehl ratios of 0.20 are measured with MOAO while achieving 0.25 with closed-loop AO in fairly similar seeing conditions (r 0 ≈ 15 cm at 0.5 μm). As expected, MOAO has performed at an intermediate level between GLAO and closed-loop AO.

Durham adaptive optics real-time controller

The Durham adaptive optics (AO) real-time controller was initially a proof of concept design for a generic AO control system. It has since been developed into a modern and powerful central-processing-unit-based real-time control system, capable of using hardware acceleration (including field programmable gate arrays and graphical processing units), based primarily around commercial off-the-shelf hardware. It is powerful enough to be used as the real-time controller for all currently planned 8 m class telescope AO systems. Here we give details of this controller and the concepts behind it, and report on performance, including latency and jitter, which is less than 10 μs for small AO systems.

First on-sky SCAO validation of full LQG control with vibration mitigation on the CANARY pathfinder

Adaptive optics provides real time correction of wavefront disturbances on ground based telescopes. Optimizing control and performance is a key issue for ever more demanding instruments on ever larger telescopes affected not only by atmospheric turbulence, but also by vibrations, windshake and tracking errors. Linear Quadratic Gaussian control achieves optimal correction when provided with a temporal model of the disturbance. We present in this paper the first on-sky results of a Kalman filter based LQG control with vibration mitigation on the CANARY instrument at the Nasmyth platform of the 4.2-m William Herschel Telescope. The results demonstrate a clear improvement of performance for full LQG compared with standard integrator control, and assess the additional improvement brought by vibration filtering with a tip-tilt model identified from on-sky data, thus validating the strategy retained on the instrument SPHERE at the VLT.

Advancements in Next-Generation Sequencing.

The term next-generation sequencing is almost a decade old, but it remains the colloquial way to describe highly parallel or high-output sequencing methods that produce data at or beyond the genome scale. Since the introduction of these technologies, the number of applications and methods that leverage the power of genome-scale sequencing has increased at an exponential pace. This review highlights recent concepts, technologies, and methods from next-generation sequencing to illustrate the breadth and depth of the applications and research areas that are driving progress in genomics.

Durham extremely large telescope adaptive optics simulation platform

Adaptive optics systems are essential on all large telescopes for which image quality is important. These are complex systems with many design parameters requiring optimization before good performance can be achieved. The simulation of adaptive optics systems is therefore necessary to categorize the expected performance. We describe an adaptive optics simulation platform, developed at Durham University, which can be used to simulate adaptive optics systems on the largest proposed future extremely large telescopes as well as on current systems. This platform is modular, object oriented, and has the benefit of hardware application acceleration that can be used to improve the simulation performance, essential for ensuring that the run time of a given simulation is acceptable. The simulation platform described here can be highly parallelized using parallelization techniques suited for adaptive optics simulation, while still offering the user complete control while the simulation is running. The results from the simulation of a ground layer adaptive optics system are provided as an example to demonstrate the flexibility of this simulation platform.

CANARY: the on-sky NGS/LGS MOAO demonstrator for EAGLE

EAGLE is a multi-object 3D spectroscopy instrument currently under design for the 42-metre European Extremely Large Telescope (E-ELT). Precise requirements are still being developed, but it is clear that EAGLE will require (~100 x 100 actuator) adaptive optics correction of ~20 - 60 spectroscopic subfields distributed across a ~5 arcminute diameter field of view. It is very likely that LGS will be required to provide wavefront sensing with the necessary sky coverage. Two alternative adaptive optics implementations are being considered, one of which is Multi-Object Adaptive Optics (MOAO). In this scheme, wavefront tomography is performed using a set of LGS and NGS in either a completely open-loop manner, or in a configuration that is only closed-loop with respect to only one DM, probably the adaptive M4 of the E-ELT. The fine wavefront correction required for each subfield is then applied in a completely open-loop fashion by independent DMs within each separate optical relay. The novelty of this scheme is such that on-sky demonstration is required prior to final construction of an E-ELT instrument. The CANARY project will implement a single channel of an MOAO system on the 4.2m William Herschel Telescope. This will be a comprehensive demonstration, which will be phased to include pure NGS, low-order NGS-LGS and high-order woofer-tweeter NGS-LGS configurations. The LGSs used for these demonstrations will be Rayleigh systems, where the variable range-gate height and extension can be used to simulate many of the LGS effects on the E-ELT. We describe the requirements for the various phases of MOAO demonstration, the corresponding CANARY configurations and capabilities and the current conceptual designs of the various subsystems.

Large area APDs and monolithic APD arrays

In this paper, development of large area planar APDs and monolithic APD arrays for scintillation detection is discussed. Single APDs with area as large as 10 cm2 have been fabricated and tested with CsI(Tl) scintillator (3.8 cm diameter, 2.5 cm high). The resolution of the 662 keV photopeak has been measured to be 9% (FWHM). Multi-element APD arrays have also been fabricated in various formats such as 4/spl times/4 to 14/spl times/14 elements (2 mm pixels) and their gain, noise and dark current performance has been characterized. Scintillation and timing studies have also been performed by coupling these arrays to LSO and CsI(Tl) scintillators. Packaging, and electronic readout issues related to these APD devices are discussed.

Open-loop tomography with artificial neural networks on CANARY: on-sky results

We present recent results from the initial testing of an artificial neural network (ANN)-based tomographic reconstructor Complex Atmospheric Reconstructor based on Machine lEarNing (CARMEN) on CANARY, an adaptive optics demonstrator operated on the 4.2m William Herschel Telescope, La Palma. The reconstructor was compared with contemporaneous data using the Learn and Apply (L&A) tomographic reconstructor. We find that the fully optimized L&A tomographic reconstructor outperforms CARMEN by approximately 5percent in Strehl ratio or 15nm rms in wavefront error. We also present results for CANARY in Ground Layer Adaptive Optics mode to show that the reconstructors are tomographic. The results are comparable and this small deficit is attributed to limitations in the training data used to build the ANN. Laboratory bench tests show that the ANN can outperform L&A under certain conditions, e.g. if the higher layer of a model two layer atmosphere was to change in altitude by ∼300m (equivalent to a shift of approximately one tenth of a subaperture).

Modeling a MEMS deformable mirror using non-parametric estimation techniques

Using non-parametric estimation techniques, we have modeled an area of 126 actuators of a micro-electro-mechanical deformable mirror with 1024 actuators. These techniques produce models applicable to open-loop adaptive optics, where the turbulent wavefront is measured before it hits the deformable mirror. The models input is the wavefront correction to apply to the mirror and its output is the set of voltages to shape the mirror. Our experiments have achieved positioning errors of 3.1% rms of the peak-to-peak wavefront excursion.

Using artificial neural networks for open-loop tomography

Modern adaptive optics (AO) systems for large telescopes require tomographic techniques to reconstruct the phase aberrations induced by the turbulent atmosphere along a line of sight to a target which is angularly separated from the guide sources that are used to sample the atmosphere. Multi-object adaptive optics (MOAO) is one such technique. Here, we present a method which uses an artificial neural network (ANN) to reconstruct the target phase given off-axis references sources. We compare our ANN method with a standard least squares type matrix multiplication method and to the learn and apply method developed for the CANARY MOAO instrument. The ANN is trained with a large range of possible turbulent layer positions and therefore does not require any input of the optical turbulence profile. It is therefore less susceptible to changing conditions than some existing methods. We also exploit the non-linear response of the ANN to make it more robust to noisy centroid measurements than other linear techniques.