Optimal transmission of pulsed laser energy to a target is essential for the maximization of reflected signal power in Debris Laser Ranging (DLR) systems. We describe the use of the PPPP measurement technique to allow compensation for both wavefront aberration, tip/tilt and errors arising from misalignment of the transmit and receive optical axes. This paper provides an update on the bistatic Wavefronts Obtained by Measuring Beam-profiles through Atmospheric Turbulence (WOMBAT) trial1 conducted with the EOS Space Systems 1.8m DLR system2 on Mt Stromlo, Australia, using an adjacent telescope to observe the 170 Hz PPPP intensity profiles.
Adaptive optics (AO) is widely used in optical/near-infrared telescopes to remove the effects of atmospheric distortion, and laser guide stars (LGSs) are commonly used to ease the requirement for a bright, natural reference source close to the scientific target in an AO system. However, focus anisoplanatism renders single LGS AO useless for the next generation of extremely large telescopes. Here, we describe proof-of-concept experimental demonstrations of a LGS alternative configuration, which is free of focus anisoplanatism, with the corresponding wavefront sensing and reconstruction method, termed projected pupil plane pattern (PPPP). This laboratory experiment is a critical milestone between the simulation and on-sky experiment, for demonstrating the feasibility of PPPP technique and understanding technical details, such as extracting the signal and calibrating the system. Three major processes of PPPP are included in this laboratory experiment: the upward propagation, return path, and reconstruction process. From the experimental results, it has been confirmed that the PPPP signal is generated during the upward propagation and the return path is a reimaging process whose effect can be neglected (if the images of the backscattered patterns are binned to a certain size). Two calibration methods are used: the theoretical calibration is used for the wavefront measurement, and the measured calibration is used for closed-loop control. From both the wavefront measurement and closed-loop results, we show that PPPP achieves equivalent performance to a Shack–Hartmann wavefront sensor.
The Canary Hosted Upgrade for High-Order Adaptive Optics is an experimental test-bench for high-order SCAO, in R-and I-bands, designed to utilize the Canary experiment at the 4.2m William Herschel Telescope. Chough consists of a pick-off that diverts light from after the 2nd DM in Canary up onto a custom breadboard which hosts the Chough sub-systems. These consist primarily of a ADC, an optical relay, a 1020-actuator DM, a 31 x 31 SH-WFS, and finally a Science Imager. Each of these sub-systems is detailed, with emphasis on interesting and unusual features. As an integrated experiment, the October/2016 on-sky engineering run is first described and then the re-integration of Chough in the laboratory during 2017 as a standalone instrument. In its latter guise, it is a host for additional instrumentation dedicated for high-order AO. An example briefly described is the CAWS interferometer, designed to produce absolute phase residual measurements over a wide chromatic bandwidth (paper #10703-212 in this meeting). We report on consequences of design decisions made for cost reasons, the bench’s fundamental performance, lessons learnt during the various stages of the project so far, and end by describing plans for Chough’s exploitation in the future for high-order SCAO research in the visible and near-IR.
PPPP, Pupil Plane Projected Pattern, is a LGS alternative (described more fully in the paper by Yang, this meeting #10703-26) which is inherently free of focal anisoplanatism. It has other practical and scientific advantages, but it is the disadvantages that this paper concentrates on since they are foremost when considering a real implementation. An on-sky test of the technique is funded and here we describe progress in solving the fundamental questions for any new technique: how to actually do it at a real telescope? Our targeted platform is a Nasmyth platform of the 4.2m WHT on La Palma. We discuss the difficulties of projecting an afocal beam from the primary mirror without causing excessive back-reflections/-scatter, which drowns the beam-profile, and instead suggest two alternative experiments. By splitting the validation of PPPP on-sky into two parts, each experiment can address a separate aspect of the validation without the disadvantage of trying to “do it all” within one experiment.
For the next generation of extremely large telescopes with the primary mirrors over 30 m in diameter, focal anisoplanatism renders single laser guide star AO useless. The laser tomography AO (LTAO) technique demonstrates an effective approach to reduce focal anisoplanatism, although it requires multiple LGSs & WFSs, and complex tomographic reconstruction. Here we propose a novel LGS alternative configuration with the corresponding wavefront sensing and reconstruction method, termed Projected Pupil Plane Pattern (PPPP). A key advantage of this method is that a single collimated beam is launched from the telescope primary mirror, and the wavefront sensed on the uplink path, which will not suffer from the effects of focal anisoplanatism. In addition, the power density of the laser beam is significantly reduced compared to a focused LGS, which decreases aircraft and satellite safety hazards. A laboratory experiment for PPPP has been setup to anchor the PPPP concept and compare against a Shack-Hartmann WFS.
CHOUGH is a small, fast project to provide an experimental on-sky high-order SCAO capability to the 4.2m WHT telescope. The basic goal has r0-sized sub- apertures with the aim of achieving high-Strehl ratios (> 0:5) in the visible (> 650 nm). It achieves this by including itself into the CANARY experiment: CHOUGH is mounted as a breadboard and intercepts the beam within CANARY via a periscope. In doing so, it takes advantage of the mature CANARY infrastructure, but add new AO capabilities. The key instruments that CHOUGH brings to CANARY are: an atmospheric dispersion compensator; a 32 × 32 (1000 actuator) MEMS deformable mirror; 31 × 31 wavefront sensor; and a complementary (narrow-field) imager. CANARY provides a 241-actuator DM, tip/tilt mirror, and comprehensive off-sky alignment facility together with a RTC. In this work, we describe the CHOUGH sub-systems: backbone, ADC, MEMS-DM, HOWFS, CAWS, and NFSI.
An astronomical adaptive optics test-bench, designed to replicate the conditions of a 4 m-class telescope, is presented. Named DRAGON-Next Generation, it is constructed primarily from commercial off-the-shelf components with minimal customization (approximately a 90:10 ratio). This permits an optical design which is modular and this leads to a reconfigurability. DRAGON-NG has been designed for operation for the following modes: (high-order) SCAO, (twin-DM) MOAO, and (twin-DM) MCAO. It is capable of open-loop or closed-loop operation, with (3) natural and (3) laser guide-star emulation at loop rates of up to 200Hz. Field angles of up-to 2.4 arcmin (4m pupil emulation) can pass through the system. The design is dioptric and permits long cable runs to a compact real-time control system which is on-sky compatible. Therefore experimental validation can be carried out on DRAGON-NG before transferring to an on-sky system, which is a significant risk mitigation.
The CANARY-Hosted Upgrade for High-Order Adaptive Optics (CHOUGH), is a narrow-field of view High- Order Single Conjugate on-sky AO demonstrator to be placed on the 4.2m WHT telescope. It aims to produce a Strehl ratio greater than 0.5 in the visible region of the spectrum (> 640nm). A High-Order wave-front sensor (HOWFS) is a central piece of the experiment; it is a Shack-Hartmann with a sampling of 31x31 subapertures across the pupil. A variable aperture spatial filter designed to reduce aliasing for high-spatial frequencies, located at a focal plane preceding the lenslet array. The HOWFS has a quad-cell configuration on the detector with a one-pixel guard ring and 48μm subaperture. The detector is a NuVu EMCCD camera, 24μm pixel size, operating at >500Hz. The lenslet array, collimator and relay are commercial off-the-shelf. This was technically challenging due to the small size of the pupil, 2.3mm, and the small optics involved in the design.
We discuss the design of a 50mm diameter Atmospheric Dispersion Corrector (ADC) for The CANARY-Hosted Upgrade for High-Order Adaptive Optics (CHOUGH). Usually to avoid pupil actuator-lenslet array mismatch, the ADC is Customarily placed very close to the pupil plane. This design aims to achieve a non-pupil conjugated ADC suitable to be located in any place inside the collimated beam path, this is due to the restrictions given by CHOUGH optical relay. The ADC also needs to satisfy the very small pupil shift requirement, for pupil stability. The ADC is of the Amici prism type, made up of two plates of cemented double prisms. The two plates counter rotate correcting for the different Zenith angles, from the Zenith up to 60°.
The Canary Hosted-Upgrade for High-Order Adaptive Optics, or CHOUGH, is an upgrade for the Canary Tomographic AO experiment. It aims to enable a high-order 30×30, single-conjugate AO capability on a 4m telescope. It utilizes a Shack-Hartmann WFS with a spatial filter for measurements together with a MEMS-DM and a magnetically actuated DM in tandem to provide the correction (dual-DM architecture). For analysis of the residuals from the correction, there are two separate instruments: a conventional imager operating in the visible part of the spectrum (V- to I-band), and an interferometer that directly measures the phase. At present the system is in the design stage and this paper reports progress towards developing a system that is capable of delivering the goals on-sky.
DRAGON is a real-time, tomographic Adaptive Optics test bench currently under development at Durham University. Optical and mechanical design work for DRAGON is now complete, and the system is close to becoming fully operational. DRAGON emulates current 4.2 m and 8 m telescopes, and can also be used to investigate ELT scale issues. The full system features 4 Laser Guide Star (LGS) Wavefront Sensors (WFS), 3 Natural Guide Star (NGS) WFSs and one Truth Sensor, all of which are 31 × 31 sub-aperture Shack-Hartmann WFS. Two Deformable Mirrors (DMs), a Boston MEMS Kilo DM and a Xinetics 97 actuator DM, correct for turbulence induced aberrations and these can be configured to be either open or closed loop of the WFS. A novel method of LGS emulation is implemented which includes the effects of uplink turbulence and elongation in real-time. The atmosphere is emulated by 4 rotating phase screens which can be translated in real-time to replicate altitude evolution of turbulent layers. DRAGON will be used to extensively study tomographic AO algorithms, such as those required for Multi-Object AO. As DRAGON has been designed to be compatible with CANARY, the MOAO demonstrator, results can be compared to those from the CANARY MOAO demonstrator on the 4.2m William Herschel Telescope. We present here an overview of the current status of DRAGON and some early results, including investigations into the validity of the LGS emulation method.
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) in La Palma since 2010. In 2013, CANARY was upgraded from its initial configuration that used three off-axis Natural Guide Stars (NGS) through the inclusion of four off-axis Rayleigh LGS and associated wavefront sensing system. Here we present the system and analysis of the on-sky results obtained at the WHT between May and September 2014. Finally we present results from the final ‘Phase C’ CANARY system that aims to recreate the tomographic configuration to emulate the expected tomographic AO configuration of both the AOF at the VLT and E-ELT.
DRAGON is a high order, wide field AO test-bench at Durham. A key feature of DRAGON is the ability to be operated at real-time rates, i.e. frame rates of up to 1kHz, with low latency to maintain AO performance. Here, we will present the real-time control architecture for DRAGON, which includes two deformable mirrors, eight wavefront sensors and thousands of Shack-Hartmann sub-apertures. A novel approach has been taken to allow access to the wavefront sensor pixel stream, reducing latency and peak computational load, and this technique can be implemented for other similar wavefront sensor cameras with no hardware costs. We report on experience with an ELT-suitable wavefront sensor camera. DRAGON will form the basis for investigations into hardware acceleration architectures for AO real-time control, and recent work on GPU and many-core systems (including the Xeon Phi) will be reported. Additionally, the modular structure of DRAGON, its remote control capabilities, distribution of AO telemetry data, and the software concepts and architecture will be reported. Techniques used in DRAGON for pixel processing, slope calculation and wavefront reconstruction will be presented. This will include methods to handle changes in CN2 profile and sodium layer profile, both of which can be modelled in DRAGON. DRAGON software simulation techniques linking hardware-in-the-loop computer models to the DRAGON real-time system and control software will also be discussed. This tool allows testing of the DRAGON system without requiring physical hardware and serves as a test-bed for ELT integration and verification techniques.
DRAGON is be a new and in many ways unique visible light adaptive optics test bench. Initially, it will test new and existing concepts for CANARY, the laser guide star tomographic adaptive optics demonstrator on the WHT, then later it will be used to explore concepts for other existing and future telescopes. Natural and Laser Guide Stars (NGS and LGS) are emulated, where the LGSs exhibit the effects of passing up through turbulence and spot elongation. AO correction is performed by one high and one low order deformable mirror, allowing woofer-tweeter control, and multiple high and low order wave front sensors detect wave front error. The Durham Adaptive Optics Real-time Controller (DARC) is used to provide real-time control over various DRAGON configurations. DRAGON is currently under construction, with the turbulence simulator completed. Construction and alignment of the system is expected to be finished in the coming year, though first results from completed modules follow sooner.
An MOAO corrected multi-IFU instrument, such as the EAGLE instrument proposed for the E-ELT has a
deformable mirror correcting each IFU sub-field. Additionally, EAGLE will also use the E-ELT deformable M4
mirror to apply a global (closed-loop) MOAO correction. Here, we investigate the impact on MOAO performance
if a global GLAO correction is applied across the whole field, rather than the optimised global MOAO correction
(which may or may not be identical). The differences in M4 correction (between GLAO and optimal MOAO)
will depend on the position of IFU pick-offs in the science field, and also on the turbulence, for example, MOAO
DM stroke may be minimised if more than the ground layer is corrected by the M4 DM, depending on how
fast turbulence decorrelates across the field of view. We consider the impact on MOAO DM stroke, the effect
on performance, and study both tomographic and non-tomographic GLAO corrections. Such a situation may
arise if for example a combined multi-object spectrograph and multi-IFU instrument is designed, such as would
result from the integration of EAGLE with another proposed E-ELT instrument. We demonstrate here that
performance of EAGLE will not be significantly affected by being placed behind another such instrument. The
results presented will be obtained using full end-to-endMonte-Carlo simulations using the Durham AO Simulation
Platform. We also present a number of algorithms which can be used to improve AO performance, both in pixel
processing and multi-mirror control.
We present a wavefront sensor design for the purpose of measuring post-AO corrected light, especially in the
cases of high-Strehl and when using natural guide stars. It is inspired by holographic design principles and
oers approximately two orders of magnitude increase in sensitivity over a conventional Shack-Hartmann design.
The theoretical design and that of a laboratory prototype are presented, together with simulation results for a
case-study of sinusoidal phase and the corresponding results from a laboratory experiment.
Numerical Simulation is an essential part of the design and optimisation of astronomical adaptive optics systems. Simulations of adaptive optics are computationally expensive and the problem scales rapidly with telescope aperture size, as the required spatial order of the correcting system increases. Practical realistic simulations of AO systems for extremely large telescopes are beyond the capabilities of all but the largest of modern parallel supercomputers. Here we describe a more cost effective approach through the use of hardware acceleration using field programmable gate arrays. By transferring key parts of the simulation into programmable logic, large increases in computational bandwidth can be expected. We show that the calculation of wavefront sensor images (involving a 2D FFT, photon shot noise addition, background and readout noise), and centroid calculation can be accelerated by factor of 400 times when the algorithms are transferred into hardware. We also provide details about the simulation platform and framework that we have developed at Durham.
As part of a collaboration between Durham University and ESO, an experimental platform is presented whose purpose is for testing generic laser-based wavefront sensors (WFS) for adaptive optics. The Rayleigh Technical Demonstrator (RTD) has been designed to allow a laser launch and Rayleigh back-scatter collection by installing components solely on a Nasmyth platform of the William Herschel Telescope, La Palma. The aim is to provide a WFS testing port within the RTD, permitting new WFS concepts to be tested rapidly in conjunction. This means that the RTD only requires small modifications for each concept to be tested. The second goal is to permit near-contemporaneous comparison of WFS data with that from a tomographic WFS. Currently, the RTD is planned to trial with three "cone effect-free" WFS concepts as part of the CALDO project. Presented here is an overview of the RTD design with detailed information on novel components and design choices.
We present a summary of activity at the Cambridge Optical Aperture Synthesis Telescope (COAST) group
during the period 2004-2006. Our main program has focused on technical design and prototyping for future
facility arrays such as the VLTI and Magdalena Ridge Observatory Interferometer, but with a small parallel
effort of focused astronomical observations with COAST, in particular multi-wavelength studies of supergiants.
We report on progress on these and other technical areas over the past 2 years.
We present a summary of the activity of the Cambridge Optical Aperture
Synthesis Telescope (COAST) team and review progress on the
astronomical and technical projects we have been working on in the
period 2002--2004. Our current focus has now moved from operating
COAST as an astronomical instrument towards its use as a test-bed for
strategic technical development for future facility arrays. We have
continued to develop a collaboration with the Magdalena Ridge
Observatory Interferometer, and we summarise the programmes we expect
to be working on over the next few years for that ambitious
project. In parallel, we are investigating a number of areas for the
European Very Large Telescope Interferometer and these are outlined
We present a summary of the status of the Cambridge Optical Aperture
Synthesis Telescope, and review developments at the array through the
period 2000-2002. Summaries of the astronomical and technical
programmes completed, together with an outline of those that are
currently in progress are presented. Since our last report two years
ago in 2000, there have been significant changes in the context for
astronomical interferometry in the UK. We review these developments,
and describe our plans for the near and intermediate term at COAST,
and with colleagues in Europe at the VLTI and in the USA at the
Magdalena Ridge Observatory in New Mexico.
The first-generation COAST array is now primarily operated as a tool
for astrophysics, with any development work aimed at improving
observing efficiency and at prototyping hardware for future arrays. In this paper we summarize the full range of astrophysical results
obtained with COAST in the previous two years. Results of a
program to investigate hotspots on red supergiant stars are
presented in detail.
A new design for a wavefront sensor suitable for low-order low-light correction is shown. The hybrid modal sensor, the Nine Element (NE) sensor, is compared with a curvature sensor and quadcell under single aperture applications. The design of the NE sensor allows the use of readily-available array detectors. We discuss the optimization of the design to maximize its performance with respect
to the number of Zernike polynomials to detect and optical parameters, using a simulated annealing technique. Numerical simulations show the good SNR response low-light levels, and indicate a reduction in wavefront variance from 6.41 rad2 to 2.01 rad2. The sensitivity to tip/tilt errors
is demonstrated to be comparable to a quadcell. Successful closed feedback loop operation results in corrected Strehl ratios of over 0.5. Improvements and future work is discussed.