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In the advanced design, construction, and commissioning phases of GMTO project, the critical role of systems engineering is tracking and managing expected observatory performance and ensuring that the scientific goals of the Giant Magellan Telescope (GMT) are met. GMTO’s approach to this role is defining Key Performance Parameters (KPPs) to measure technical performance. A set of KPPs have been established to assess the performance of the telescope through construction and Assembly, Integration, Verification, and Commissioning (AIVC). Each KPP has a threshold value representing the minimum acceptable performance, and an objective value representing the desired operational performance. KPPs are used to prioritize maturation plans for technologies and novel system-level design strategies. The KPPs directly characterize the performance of the telescope by ensuring focal plane (image), exit pupil (wavefront) and light collecting capabilities of the telescope. The paper demonstrates that the chosen KPPs properly represent key science capabilities, as image size, sensitivity, photometric, and astrometric accuracy. It is also shown how detailed error budgets link the KPPs to component technical specifications that in turn are closely monitored by simulations. Integrated modeling is crucial for the performance-based systems engineering approach of defining and then evaluating the objective and threshold levels for the KPPs. As described in other GMTO paper at this conference, contributions from individual subsystems and components are modeled to determine their effect on system performance. We describe how GMTO has implemented KPPs and is now using them to guide and coordinate technical development.

System engineering at GMTO is using a comprehensive integrated model that integrates seamlessly, in a unified framework, finite element, optics, and control models. A computational fluid dynamics (CFD) model of the observatory is also used to estimate dome seeing, wind jitter, structural thermal deformations, and observatorywide design optimization. The GMT integrated modeling group realizes various studies for different subsystems of the project that provides the basis for the subsystem level design trades. It also assists system engineering by performing top-down and bottom-up requirements verification, error budget derivation, and operational strategies optimization. Integrated modeling will also support system engineering during the assembly, integration, verification, and commissioning phase of the project. For example, system engineering relies on the integrated model to estimate the key performance parameters (KPP) of the project. The KPP are performance metrics that will be used to validate the completion of the observatory and to confirm its readiness with respect to the start of science observation. In the paper, we give a system-level overview of the integrated model, including a description of each sub-model and of the framework that binds them together. The paper also describes how system engineering is using the integrated model for the derivation of the error budgets and of the top-down requirements flowing down from the science requirements to the lower level of subsystem engineering requirements; and how as the design of the subsystems progress, integrated modeling is then used to validate, bottom-up, the same requirements from subsystem engineering requirements back up to the science requirements with respect to the observatory performance metrics.

The Giant Magellan Telescope will be a 25.4-m visible and infrared telescope at Las Campanas Observatory. The optical design consists of 7 8.4-m primary mirror segments that reflect light to 7 secondary mirror segments in a doubly-segmented direct Gregorian configuration. Each mirror pair must be coaligned and co-boresighted. During operations, the alignment of the optical components will deflect due to variations in temperature, gravity-induced structure flexure of the mount, and, on a scale relevant to phasing, vibrations. The doubly-segmented nature and size of the GMT will create a novel set of challenges for initial assembly, integration, and verification and maintaining high-precision alignment of the optical elements during operations. GMT is developing a Telescope Metrology System that uses 3D laser metrology systems to decrease the complexity of alignment and increase observatory efficiency. This paper discusses the 4 subsystems of TMS as well as their operational modes.

Tomographic wavefront reconstruction is the main computational bottleneck to realize real-time correction for turbulence-induced wavefront aberrations in future laser-assisted tomographic adaptive-optics (AO) systems for ground-based giant segmented mirror telescopes because of its unprecedented number of degrees of freedom, N, i.e., the number of measurements from wavefront sensors. In this paper, we provide an efficient implementation of the minimum-mean-square error (MMSE) tomographic wavefront reconstruction, which is mainly useful for some classes of AO systems not requiring multi-conjugation, such as laser-tomographic AO, multi-object AO, and ground-layer AO systems, but is also applicable to multi-conjugate AO systems. This work expands that by Conan [Proc. SPIE9148, 91480R (2014)PSISDG0277-786X10.1117/12.2054472] to the multi-wavefront tomographic case using natural and laser guide stars. The new implementation exploits the Toeplitz structure of covariance matrices used in an MMSE reconstructor, which leads to an overall O(N log N) real-time complexity compared with O(N

We present a summary of the cryogenic detector preamplifier development programme under way at the ANU. Cryogenic preamplifiers have been demonstrated for both near-infrared detectors (Teledyne H1RG and Leonardo SAPHIRA eAPD as part of development for the GMTIFS instrument) and optical CCDs (e2v CCD231-84 for use with the AAT/Veloce spectrograph). This approach to detector signal conditioning allows low-noise instrument amplifiers to be placed very close to an infra-red detector or optical CCD, isolating the readout path from external interference noise sources. Laboratory results demonstrate effective isolation of the readout path from external interference noise sources. Recent progress has focussed on the first on-sky deployment of four cryogenic preamp channels for the Veloce Rosso precision radial velocity spectrograph. We also outline future evolution of the current design, allowing higher speeds and further enhanced performance for the demanding applications required for the on instrument wavefront sensor on the Giant Magellan Integral Field Spectrograph (GMTIFS).

The Giant Magellan Telescope (GMT) M1 Subsystem includes the seven 8.4 meter M1 (Primary) Segment Mirrors and the steel mirror cell weldments which house the mirror active support and thermal control systems. The segmented nature of the primary mirror and the requirement that each of the six off-axis segment cells be interchangeable impose requirements on the range of motion and control beyond those applicable to the M1 subsystems on 6.5m and 8.4m telescopes using the structured honeycomb mirrors.The subsystem is both technically challenging to design and costly to produce. The M1 Subsystem is allocated a large fraction of the GMT natural seeing image quality budget. Support actuator tolerances, range of motion, accuracy, and precision, as well as the ability of the thermal control system to regulate the primary mirror temperature, all have a significant effect on the image quality. The authors have developed several linear models to estimate the effect of force and moment errors at the M1 Segment Active Supports and the non-uniformity of temperature across M1 segments on the delivered image quality. These results are coupled to the Wavefront Control Subsystem model and are integrated into the GMT system-level simulations to produce a final image quality budget and to quantify the effectiveness of the Wavefront Control Subsystem to compensate for M1 Subsystem error. In this paper, we present the modeling process and preliminary performance results obtained using the models.

The Giant Magellan Telescope (GMT) wavefront control system will provide active optics control and optimized atmospheric turbulence correction to every instrument on the 25.4 m diameter GMT. All subsystems of the GMT wavefront control system have passed their preliminary design reviews, and several are now in the detailed design and prototyping phases. Significant progress has been made developing optimized control algorithms, and simulating observatory performance over a wide range of environmental conditions. We review the wavefront control strategy in each observing mode, and the associated image quality error budgets. We also describe recent d and prototyping progress, and our plans to complete the wavefront control system development and prepare for first light.

The Giant Magellan Telescope (GMT) is going to be a complex and versatile exploration machine, which makes systems engineering GMT challenging. This paper addresses three particularly critical aspects of systems engineering: a general and flexible definition of the observatory, image quality specifications, and compliance assessment for statistical performance requirements. The observatory definition and its high-level flow down is captured in a set of Foundation Documents, from level-1 (stakeholders’ intentions and the objective specifications of science data) through level-2 (engineering specification) to level-3 (architectural design and operational concepts). Image quality requirements for atmospheric resolution modes are balancing observing efficiency considerations and system capabilities enabling exceptional image quality under the best conditions. To address statistical specifications, requirements validation and early design verification is carried out in an integrated modeling framework that takes advantage of sequential Monte- Carlo analysis over the Standard Year, representing our understanding of correlated summit conditions and GMT operational constraints.

The 25.4 m Giant Magellan Telescope (GMT) consists of seven 8.4 m primary mirror (M1) segments with matching segmentation of the Gregorian secondary mirror (M2). The GMT will operate in four basic optical correction modes, Natural Seeing (NS), Ground Layer Adaptive Optics (GLAO), Natural Guide Star Adaptive Optics (NGAO) and Laser Tomography Adaptive Optics (LTAO). Each of these modes must deliver a specified combination of image quality, field of view, and sky coverage over a range of environmental conditions. With a double segmented mirror configuration, even in the simplest of the correction modes the GMT includes over one thousand controllable degrees of freedom. Exogenous and internal sources of disturbances and noise over these degrees of freedom will limit the image quality. The different ranges of motion and bandwidth of the different degrees of freedom enable a cascade correction of the wavefront error, successively rejecting global to local disturbances. This frequency and spatial separation allows allocating the disturbances in stages, considering the residuals of the low spatial and temporal corrections as the disturbance for the high order corrections. While a first approach can consider the analysis of systems in isolation in order to allocate coarse budgets, a complex control system such as that of the GMT requires a Dynamic Optics Simulation (DOS) to account for the real interactions between the controlled plant and the controllers. For example, some control loops such as the M1 figure control system will have an update rate of only 0.03 Hz, while the Adaptive Secondary Mirror (ASM) will be updated at 1kHz . The DOS is an end-to-end simulation environment that brings together optics, finite element models (FEM), mechanical motions, surface deformations and control models applied to the GMT main optics. At the center of the DOS there is an optics propagation module with both geometric ray tracing and Fourier propagation capability. The dynamic response of the telescope mount and the large M1 segments has been modeled by applying Craig-Bampton reduction analysis to finite element models. These reductions have been reordered in a second order form, allowing higher computational efficiency than traditional state space models. Each M1 segment is controlled by an array of 330 actuators with realistic precision, noise and discretization errors. The structural dynamics model can be used in time domain simulations that account for all the non-linear effects of actuators and sensors, or in a linear frequency domain model to run more efficiently stochastic analyses. A high resolution Computational Fluid Dynamics (CFD) model has been developed for simulating unsteady turbulent flow over the optical system. These simulations provide unsteady pressure fluctuations over the main optics and effects of varying index of refraction in the optical path for different operating conditions. These quantities are subsequently used for estimating wind induced image jitter and thermal (dome and mirror) seeing by applying the combined structural, control, and optical models described above. The DOS allows GMT to understand the sensitivity of image quality to any of the thousands of parameters of our plant and control system., Due to the cascade layers of control loops, DOS allows specifying design parameters without over-constraining the solution space.

The recent availability of large format near-infrared detectors with sub-election readout noise is revolutionizing our approach to wavefront sensing for adaptive optics. However, as with all near-infrared detector technologies, challenges exist in moving from the comfort of the laboratory test-bench into the harsh reality of the observatory environment. As part of the broader adaptive optics program for the GMT, we are developing a near-infrared Lucky Imaging camera for operational deployment at the ANU 2.3 m telescope at Siding Spring Observatory. The system provides an ideal test-bed for the rapidly evolving Selex/SAPHIRA eAPD technology while providing scientific imaging at angular resolution rivalling the Hubble Space Telescope at wavelengths λ = 1.3-2.5 μm.

We investigate the tip-tilt sensor for the laser tomography adaptive optics system of the Giant Magellan Telescope. In the case of the GMTIFS instrument, we require high Strehl over a moderate region of the sky and high throughput with very high sky coverage. In this paper, we simulate the performance of a K-band tip-tilt sensor using an eAPD array. The paper presents a comparison of different centroiding techniques and servo controllers. In addition, we explore the possibility of using the wavefront sensors (WFSs) used in the ground layer adaptive optics (GLAO) mode to supplement the tip-tilt sensor measurement. The imaging requirement is almost met using the correlation algorithm to estimate the displacement of the spot, along with a high-order controller tailored to the telescope wind shake. This requires a sufficiently bright star to be able to run at 500 Hz, so the sky coverage is limited. In the absence of wind, then the star can be fainter and the requirement is met. The spectroscopy requirement is met even in the case of high wind. The results are even better if we use the GLAO WFSs as well as the tip-tilt sensors. Further work will explore the viability of inserting a DM in the OIWFS and the resulting tip-tilt performance.

The 25.4m Giant Magellan Telescope consists of seven 8.4 m primary mirror (M1) segments with matching segmentation of the Gregorian secondary mirror (M2). When operating the telescope in the diffraction-limited Adaptive Optics (AO) observing modes, the M1-M2 pairs of segments must be phased to a small fraction of the observing wavelength. To achieve this level of correction, the phasing system uses multiple natural guidestar phasing sensors deployed across the field of view to provide an absolute phasing references to edge sensors bridging the gaps between segments. We will present in this paper the performance characterization of the GMT phasing system based on end-to-end numerical simulations performed with the Dynamic Optical Simulation (DOS) tool, which integrates the optical and mechanical dynamics models of the GMT with the Fourier optics models of AO and phasing sensors. The expected phasing performance under different observing conditions will be presented.

This article describes the design, implementation and characterization of a novel optical tweezer system. The system utilizes a deformable mirror, wavefront sensor and controller to manipulate an optically trapped micro-particle within a small chamber. This method for optical trapping employs technology adopted from astronomical instrumentation; in particular, adaptive optics. A deformable mirror is employed to control the wavefront phase of a laser beam before it is imaged into a chamber by a high numerical aperture microscope objective lens. The wavefront phase is measured by a Shack–Hartman wavefront sensor and the particle's position monitored by a video camera. The goals of the work presented here are to trap particles ranging in size from 1 μm to 10 μm; create a suitable controller for moving trapped particles in three dimensions; image the trapped particle; determine the prototype system's performance specifications; and determine the trap stiffness.

The first measurements of the spatial coherence outer scale at the Observatorio Astronomico Nacional at San Pedro Martir (OAN-SPM) are reported along with long term seeing measurements. These parameters were measured with the Generalized Seeing Monitor and with a Dierential Image Motion Monitor. An instrumented mast was also used to mea- sure the structure constant of the refractive index C 2 in the first 15 m. Log-normal statistics were found for the seeing and for the outer scale, with median values of 0:92 00 and 27.0 m, respectively. The distribution of the outer scale values is similar to that found in other observatories around the world, suggesting that the presence of trees in the OAN-SPM do not aect the outer scale values. Correlation studies suggest that large values of the seeing and the outer scale are likely to occur when the wind blows from the SSW. Further studies are recommended to confirm this tendency.

Object-Oriented Matlab Adaptive Optics (OOMAO) is a Matlab toolbox dedicated to Adaptive Optics (AO) systems. OOMAO is based on a small set of classes representing the source, atmosphere, telescope, wavefront sensor, Deformable Mirror (DM) and an imager of an AO system. This simple set of classes allows simulating Natural Guide Star (NGS) and Laser Guide Star (LGS) Single Conjugate AO (SCAO) and tomography AO systems on telescopes up to the size of the Extremely Large Telescopes (ELT). The discrete phase screens that make the atmosphere model can be of infinite size, useful for modeling system performance on large time scales. OOMAO comes with its own parametric influence function model to emulate different types of DMs. The cone effect, altitude thickness and intensity profile of LGSs are also reproduced. Both modal and zonal modeling approach are implemented. OOMAO has also an extensive library of theoretical expressions to evaluate the statistical properties of turbulence wavefronts. The main design characteristics of the OOMAO toolbox are object-oriented modularity, vectorized code and transparent parallel computing. OOMAO has been used to simulate and to design the Multi-Object AO prototype Raven at the Subaru telescope and the Laser Tomography AO system of the Giant Magellan Telescope. In this paper, a Laser Tomography AO system on an ELT is simulated with OOMAO. In the first part, we set-up the class parameters and we link the instantiated objects to create the source optical path. Then we build the tomographic reconstructor and write the script for the pseudo-open-loop controller.

The Advanced Instrumentation and Technology Center at the Australian National University is building a Laser Tomography Adaptive Optics Test Bed for Extremely Large Telescopes. The optical test bench is using three Laser Guide Stars (LGS) propagating through three phase screens. The LGS wavefronts are sampled with a 16 × 16 Shack-Hartmann wavefront sensor (SH-WFS). Cone effect, spot elongation and Sodium layer density fluctuations are reproduced on the bench. Two Natural Guide Stars (NGS), on-axis and off-axis, are also added to the bench. The wavefront of the on-axis NGS is corrected with a DM located in the optical path of both the LGSs and the on-axis NGS. The DM commands are derived from the tomographic estimate of the on-axis NGS wavefront using the measurements of the 3 LGS WFSs. The off-axis NGS wavefront is sampled with a 6 × 6 SH-WFS and is emulating tip-tilt, focus and truth sensing. A DM located in front of the off-axis NGS WFS is correcting the off-axis NGS wavefront. The commands of this DM are also derived from the tomographic reconstructor. In the paper, the design of the LTAO test bed is presented.

The estimation of a corrugated wavefront after propagation through the atmosphere is usually solved optimally with a Minimum-Mean-Square-Error algorithm. The derivation of the optimal wavefront can be a very computing intensive task especially for large Adaptive Optics (AO) systems that operates in real-time. For the largest AO systems, efficient optimal wavefront reconstructor have been proposed either using sparse matrix techniques or relying on the fractal properties of the atmospheric wavefront. We propose a new method that exploits the Toeplitz structure in the covariance matrix of the wavefront gradient. The algorithm is particularly well-suited to Shack-Hartmann wavefront sensor based AO systems. Thanks to the Toeplitz structure of the covariance, the matrices are compressed up to a thousand-fold and the matrix-to-vector product is reduced to a simple one-dimension convolution product. The optimal wavefront is estimated iteratively with the MINRES algorithm which exhibits better convergence properties for ill-conditioned matrices than the commonly used Conjugate Gradient algorithm. The paper describes, in a first part, the Toeplitz structure of the covariance matrices and shows how to compute the matrix-to-vector product using only the compressed version of the matrices. In a second part, we introduced the MINRES iterative solver and shows how it performs compared to the Conjugate Gradient algorithm for different AO systems.

A method to generate the turbulence measurements of a Shack–Hartmann wavefront sensor is presented. Numerical simulations demonstrate that the spatial and temporal statistic properties of the slopes are respected, allowing us to generate the turbulence wavefront gradient corresponding to both natural and laser guide stars, as well as time series in accordance with the frozen flow model.

The performance of modal Multi-Conjugate Adaptive Optics systems correcting a nite number of Zernike modes is studied using a second-order statistical analysis. Both natural and laser guide stars (GS) are considered. An optimized command matrix is computed from the covariances of atmospheric signals and noise, to minimize the residual phase variance averaged over the eld of view. An ecient way to calculate atmospheric covariances of Zernike modes and their projections is found. The modal covariance code is shown to reproduce the known results on anisoplanatism and the cone eect with single GS. It is then used to study the error of wave-front estimation from several o-axis GSs (tomography). With increasing radius of the GS constellation , the tomographic error increases quadratically at small , then linearly at larger when incomplete overlap of GS beams in the upper atmospheric layers provides the major contribution to this error, especially on low-order modes. It is demonstrated that the quality of turbulence correction with two deformable mirrors is practically independent of the conjugation altitude of the second mirror, as long as the command matrix is optimized for each conguration.

The main atmospheric optical parameters (AOP) have been measured during 10 nights in April 1998 with the GSM instrument at the Moroccan site of Oukaimeden. These parameters are of interest for the optimization of high angular resolution techniques. During this campaign the temporal evolution of the AOP and their distributions have been studied. The outer scale presents a log-normal histogram with a median value of 31 m which is rather similar to the values obtained at other sites visited with GSM. The selection of the Oukaimeden site is the result of several topographical and meteorological studies on the Atlas mountain chain. Since 1988 this site has been chosen for the installation of one of the IRIS (International Research of the Interior of the Sun) stations. Here, we present the whole AOP data measured with GSM during this campaign. The main photometric and meteorological conditions of this site are also presented.

Main atmospheric parameters characterizing the turbulence were measured at the Paranal ESO Observatory (Chile) with the Generalized Seeing Monitor (GSM) during 19 nights in November{December 1998. The median seeing for this period was 0:88 00 , a little worse than average, the spatial coherence outer scale of the wavefrontL0 =2 2:0 m and the median isoplanatic angle 0 =1 :90 00 . A very good agreement with seeing values given by ESO DIMM was found. Eects of ground layer turbulence were estimated from measurements of temperature micro{fluctuations at several altitudes. These measurements revealed that the rst 21 m above ground account for 12.5% of the total turbulent energy. Comparison between GSM and ESO DIMM values have permitted to highlight a local phenomenon which occurs sometimes at the site in the middle of the night. Statistics of the refractive index structure constant C 2 n in the surface layer is also studied.

Integrated optic segment piston sensor (IOPS) for the Giant Magellan Telescope (GMT) uses single mode laser written waveguides to measure segment piston (axial alignment) of the GMT primary mirrors. Light in the H-band (from 1.5 to 1.6 μm) incident on each segment originating from an off-axis guide star is coupled into separate laser written single mode waveguides in a fused silica substrate. The waveguide inputs are positioned at the focus of a lenslet array with the same hexagonal geometry as the GMT pupil. Light from neighbouring segments is interfered in several coupling regions where waveguides are in spatial proximity allowing coupling, in order to produce an interference signal at the output. The output signal magnitude is directly related to the phase difference at the waveguide input, originating from the segment piston. Three coupling regions achieve this by splitting the light into one reference, and two signal lines. The reference provides a measurement of the amount of light coupled into the input waveguide, while each signal line is passed on to other couplers to be interfered with light from two neighbouring segments.

Space debris in low Earth orbit below 1500km is becoming an increasing threat to satellites and spacecrafts. Radar and laser tracking are currently used to monitor the orbits of thousands of space debris and active satellites are able to use this information to manoeuvre out of the way of a predicted collision. However, many satellites are not able to manoeuvre and debris-on debris collisions are becoming a signicant contributor to the growing space debris population. The removal of the space debris from orbit is the preferred and more definitive solution. Space debris removal may be achieved through laser ablation, whereby a high power laser corrected with an adaptive optics system could, in theory, allow ablation of the debris surface and so impart a remote thrust on the targeted object. The goal of this is to avoid collisions between space debris to prevent an exponential increase in the number of space debris objects. We are developing an experiment to demonstrate the feasibility of laser ablation for space debris removal. This laser ablation demonstrator utilises a pulsed sodium laser to probe the atmosphere ahead of the space debris and the sun reflection of the space debris is used to provide atmospheric tip{tilt information. A deformable mirror is then shaped to correct an infrared laser beam on the uplink path to the debris. We present here the design and the expected performance of the system.

The GMT laser tomography adaptive optics (LTAO) system design has a truth sensor guiding on a natural guide star. The truth sensor is used to measure telescope segment piston errors and measure slowly varying non- common path aberrations. The challenge lies in measuring segment piston using faint natural guide stars and the wavefront delivered by the LTAO system. This requires a sensor that can make a direct phase measurement. It is demonstrated that an infrared, AO-corrected, unmodulated pyramid or roof wavefront sensor can make the required measurements at 10 Hz for stars brighter than magnitude 17 at H- or K-band.

Error budgets are an indispensable tool for assuring that project requirements can be and are being met. An error budget will typically include terms associated with subsystems which are being designed by different teams of engineers, and fabricated by different vendors. It is a useful tool at all levels of design since it provides a means to negotiate design trades in the broadest possible context. Error budgeting is in many ways fundamental to the mission of systems engineering and of course to the overall project success. In this paper we will describe the GMT Adaptive Optics System flow down requirements and their integration with their wavefront error budgets. We will focus on the GMT Adaptive Optics wavefront error budgets for the following observing modes: Natural Guide Star Adaptive, Laser Tomography Adaptive Optics and Ground Layer Adaptive Optics. Finally, a description of the error budgets and the close link between the error budgets and other parameter such as sky coverage, zenith angle, etc., will be discussed in this paper.

The Giant Magellan Telescope (GMT) adaptive optics (AO) system will be an integral part of the telescope, providing laser guidestar generation, wavefront sensing, and wavefront correction to every instrument currently planned on the 25.4 m diameter GMT. There will be three first generation AO observing modes: Natural Guidestar, Laser Tomography, and Ground Layer AO. All three will use a segmented adaptive secondary mirror to deliver a corrected beam directly to the instruments. The Natural Guidestar mode will provide extreme AO performance, with a total wavefront error less than 185 nm RMS using bright guidestars. The Laser Tomography mode uses 6 lasers and a single off-axis natural guidestar to deliver better than 290 nm RMS wavefront error at the science target, over 50% of the sky at the galactic pole. The Ground Layer mode uses 4 natural guidestars on the periphery of the science field to tomographically reconstruct and correct the ground layer AO turbulence, improving the image quality for wide-field instruments. A phasing system maintains the relative alignment of the primary and secondary segments using edge sensors and continuous feedback from an off-axis guidestar. We describe the AO system preliminary design, predicted performance, and the remaining technical challenges as we move towards the start of construction.

The Laser Tomographic Adaptive Optics system for Giant Magellan Telescope (GMT) uses a single conjugated deformable mirror, the segmented Adaptive Secondary Mirror (ASM), to correct atmospheric wavefront aberrations with the help of a constellation of six laser beacons equally spaced on the sky. We will present different approaches for the design of the Laser Guide Star (LGS) Wave Front Sensor (WFS) system for GMT to cover all sodium emission altitudes and telescope elevations, from 80 km to 200 km range and how the preliminary design was derived from these approaches. The designed LGS WFS system includes a defocus-compensation mechanism working with a simple zooming optics to achieve the pupil image with constant pupil size, nearly constant wavefront correction, as well as pupil distortion correction. Either a trombone-mirror structure or a direct LGS-WFS translation is used for the defocus compensation, when conjugating the LGS altitudes in the sky. In the designs, a zooming collimator images the ASM in the GMT at the exit pupil of the LGS WFS system, where the designed lenslet-array is tailored for the selected CCD format for the required plate scale on the sky. Additionally, we have proposed a novel and simple solution for pupilimage segmentation when working with smaller CCD arrays. This novel solution consists of a single multi-aperture blaze grating for pupil segmentation in the system.

A novel closed-loop control technique for adaptive optics (AO) systems based on a wavelet-based phase reconstruction technique and a woofer–tweeter controller is presented. The wavelet-based reconstruction technique is based on obtaining a Haar decomposition of the phase screen directly from gradient measurements and has been extended here with the use of a Poisson solver to improve performance. This method is O(N) (i.e., a linear computation cost as number of actuators increases) and is the fastest of the known O(N) reconstruction techniques. The controller configuration is based on the woofer–tweeter controller to control low- and high-spatial-frequency aberrations, respectively. The separation of the woofer and tweeter signals is done using a computationally efficient method that is based on the availability of a low-spatial-resolution reconstruction during the wavelet synthesis process. The performance of the proposed technique is evaluated using a simulated AO system and phase screens generated to reflect atmospheric turbulence with various dynamic characteristics. Results indicate that the combination of the wavelet-based phase reconstruction and woofer–tweeter controller leads to very good results with respect to speed and accuracy.

This article reports the progress made at the University of Victoria AO Lab, regarding the realtime open-loop control of a 1024-actuator MEMS deformable mirror (DM). The setup is an hybrid woofer-tweeter/open-loop bench. A tip-tilt mirror and a woofer DM (a 57-actuator CILAS DM) are driven in closed-loop while a 1024-actuator MEMS DM is utilized on a parallel open-loop path. Previous work shows that open-loop control providing low residual error (with frozen Kolmogorov turbulence) can be obtained without the need of DM modelling. A preliminary methodical calibration of the DM is employed instead. The MEMS electronics were upgraded to an update rate of 500 Hz and the experiment lays the groundwork for showing how these performances can also be achieved on the bench with dynamic turbulence (created with custom hot air turbulence generators). The current status of the experiment and the next milestones are presented.

Variations of the sodium layer altitude and atom density profile induce errors on laser-guide-star (LGS) adaptive optics systems. These errors must be mitigated by (i), optimizing the LGS wavefront sensor (WFS) and the centroiding algorithm, and (ii), by adding a high-pass filter on the LGS path and a low-bandwidth natural-guide-star WFS. In the context of the ESO E-ELT project, five centroiding algorithms, namely the centre-of-gravity (CoG), the weighted CoG, the matched filter, the quad-cell and the correlation, have been evaluated in closedloop on the University of Victoria LGS wavefront sensing test bed. Each centroiding algorithm performance is compared for a central versus side-launch laser, different fields of view, pixel sampling, and LGS flux.

Since the early days, many aspects of Adaptive Optics (AO) have seen tremendous changes. From the early experimental systems providing low order correction in a tiny patch of sky to todays fully automated specialized system offering correction in a much wider field and/or a much higher degree of correction, the evolution has been remarkable. For example, deformable mirror (DM) technology and wavefront sensing methods have been constantly improved. As well, real-time control algorithms have been greatly refined. This paper will review the different real-time control strategies that have been used with astronomical adaptive optics. They all have in common the same objective, that is the derivation of an optimal command for the deformable mirror(s) in order to get the least amount of residual optical aberrations in the science path. Most of the time, the real-time control algorithm is split in two independent components, the first part performing the wavefront (spatial) reconstruction, the second part performing the temporal control. With the advent of the extremely large telescopes (ELTs), as well as new AO modalities requiring several DMs and wavefront sensors, performing both these tasks in an ever shrinking glimpse of time is even more challenging. We will describe advanced fast and iterative reconstruction methods recently proposed for next generation AO systems. We will show how these algorithms combined with sparse matrices and parallel computing techniques meet the requirements of Extremely Large Telescope (ELT) real time computers.

Adaptive optics (AO) is essential for many elements of the science case for the Thirty Meter Telescope (TMT). The initial requirements for the observatory’s facility AO system include diffraction-limited performance in the near IR, with 50 per cent sky coverage at the galactic pole. Point spread function uniformity and stability over a 30 arc sec field-ofview are also required for precision photometry and astrometry. These capabilities will be achieved via an order 60x60 multi-conjugate AO system (NFIRAOS) with two deformable mirrors, six laser guide star wavefront sensors, and three low-order, IR, natural guide star wavefront sensors within each client instrument. The associated laser guide star facility (LGSF) will employ 150W of laser power at a wavelength of 589 nm to generate the six laser guide stars. We provide an update on the progress in designing, modeling, and validating these systems and their components over the last two years. This includes work on the layouts and detailed designs of NFIRAOS and the LGSF; fabrication and test of a full-scale prototype tip/tilt stage (TTS); Conceptual Designs Studies for the real time controller (RTC) hardware and algorithms; fabrication and test of the detectors for the laser- and natural-guide star wavefront sensors; AO system modeling and performance optimization; lab tests of wavefront sensing algorithms for use with elongated laser guide stars; and high resolution LIDAR measurements of the mesospheric sodium layer. Further details may be found in specific papers on each of these topics.

Along with the expected ELTs comes the diversification of Ada ptive Optics (AO) systems. Most AO are beginning to make extensive use of laser guide stars (LGS), to increase sky coverage and produce a bright beacon in order to reduce wavefront measurement errors and improve performance. However, because of the larger size of the next generation of telescopes, the elonga tion seen in a Shack-Hartmann Wavefront Sensor is larger, i.e up to 7" for a 30m telescope. With such an elongation, both photon and read noise will increase and distribution variations of sodium atoms in the sodium layer start to matter. In this paper, we conduct Shack- Hartmann simulations at the sub-aperture level made with real sodium profiles taken at Lick Observatory. We will compare focus on two methods of centroiders: the matched filt er and the correlation. We then compare results with data taken form a real bench at Uvic in the particular case of NFIRAOS AO system for TMT. The goal is to better understand the impact of such variations on the final e rror budget for the WFS. Enoise includes the CCD noise sources (readout noise and dark current), photon noise and the back- ground noise due to Rayleigh scattering of the projected laser light. ELin is due to non-linearity because of under-sampling and truncation of the LGS spot image. They have also been studied in (3) in the context of Gaussian spot. Esodium is the error due to the structure and time variability in the L GS im- ages due to variability of the sodium layer, Eresp is due to the response coe cient not equal to unity, EDi the error due to the di raction spikes in each SHWFS subaperture, and, Eatm is the error due to the atmosphere considering only speckle. We will not focus on this term in this paper. The main goal of this paper is to study the impact of the sodium variations on the wavefront measurements and compare Esodium to Enoise. The field of view of each subaperture considered in this paper will be large enough to neglect the non-linearity e ects. The geometry used here is the normal cartesian CCD. In this paper, we will only talk about the case of the central launch, leading to symmetric spots, to quantify the impact of the sodium variations on the wavefront error.

Sodium Laser Guide Stars (LGS) induce optical aberrations in adaptive optics (AO) systems.The artificial star is elongated due to the sodium layer thickness, and the variations of thesodium layer altitude and atom density profile induce errors on centroid measurements ofelongated spots. In AO systems, these errors generate spurious optical aberrations, termed LGSaberrations, especially with ELTs for which the spot elongation is greater. According toanalytical models and experimental results obtained with the University of Victoria LGS benchdemonstrator, we characterized the main LGS aberrations and studied two options to mitigatethem: the Radial Thresholding and the temporal filtering., 1st AO4ELT conference - Adaptive Optics for Extremely Large Telescopes, June 22-26, 2009, Paris, France

In order to evaluate the potential of MEMS deformable mirrors for open-loop applications, a complete calibration process was performed on a 1024-actuator mirror. The mirror must be perfectly calibrated to obtain deterministic membrane deflection. The actuator's stroke-voltage relationship and the effect of the non- additivity of the influence functions are studied and finally integrated in an open-loop control process. This experiment aimed at minimizing the residual error obtained in open-loop control., Comment: 6 pages, 9 figures, Proceedings of the 1st AO for ELT conference, June 2009, Paris

Sodium Laser Guide Stars (LGSs) are elongated sources due to the thickness and the finite distance of the sodium layer. The fluctuations of the sodium layer altitude and atom density profile induce errors on centroid measurements of elongated spots, and generate spurious optical aberrations in closed--loop adaptive optics (AO) systems. According to an analytical model and experimental results obtained with the University of Victoria LGS bench demonstrator, one of the main origins of these aberrations, referred to as LGS aberrations, is not the Centre-of-Gravity (CoG) algorithm itself, but the thresholding applied on the pixels of the image prior to computing the spot centroids. A new thresholding method, termed ``radial thresholding'', is presented here, cancelling out most of the LGS aberrations without altering the centroid measurement accuracy., 8 pages, 9 figures, accepted for publication in MNRAS

An adaptive optics (AO) test bed has been designed and implemented to evaluate the effectiveness of the next generation of AO components and their associated control system. The optical design presented herein incorporates a turbulence generator, tip-tilt mirror, 140-actuator micro-electro-mechanical-system (MEMS) deformable mirror, Shack-Hartmann wave front sensor, and a science camera. This system has been operated in a closed AO loop at a 261 Hz sample rate. This paper focuses on the performance of the MEMS DM. It was examined using an interferometer to determine the influence functions, response time, and the quadratic relationship of displacement of the actuators to an applied voltage.

We introduce robust order N algorithms to estimate model parameters and control DMs in open loop based on the Vogel-Yang model for deformable mirrors appearing in JOSA-A, 23, pp. 1074-1081, 2006.

The UVic AO laboratory has build an optical test-bed reproducing LGS wavefront sensing with Shack-Hartmann WFSs on ELTs. The test bench has been used to compare self-referenced version of the center-of-gravity, quad-cell and matched-filter algorithms.

Sodium laser guide stars (LGSs) allow, in theory, full sky coverage, but have their own limitations. Variations of sodium layer altitude, thickness and atom density profile induce changing errors on wavefront measurements (LGS aberrations), especially with ELTs for which the LGS spot elongation is larger. In the framework of the Thirty-Meter-Telescope project (TMT), the AO-Lab of the University of Victoria (UVic) built a LGS-simulator test bed in order to assess the performance of new centroiding algorithms for LGS Shack-Hartmann wavefront sensors (SH-WFS). The principle of the LGS-bench is briefly reviewed. The closed-loop performances of the matched filter (MF) algorithm on laboratory 29x29 elongated spot images are presented and compared with the centre of gravity (CoG). The ability of the MF to track the LGS aberrations is successfully demonstrated. The UVic LGS-bench is not limited to SH-WFS and can serve as a LGS-simulator test bed to any other LGS-AO projects for which sodium layer fluctuations are an issue.

The Adaptive Optics Laboratory at the University of Victoria (Canada) and the Subaru Telescope NAOJ (Hawaii) are collaborating to develop a simple method allowing open-loop control of MEMS deformable mirrors. This method consists of an iterative algorithm based on 3 simple equations and 4 constants. The 4 constants are different for each mirror, therefore a characterization step is necessary to evaluate their values for a given mirror. In this paper we describe the model and the 3 equations it relies on. We also propose a characterization methodology and finally present the preliminary results respectively obtained on Victoria and Subaru test beds.