This PDF file contains the front matter associated with SPIE Proceedings Volume 8149, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.

The Large Binocular Telescope (LBT) is a unique telescope featuring two co-mounted optical trains with 8.4m primary mirrors. The telescope Adaptive Optics (AO) system uses two innovative key components, namely an adaptive secondary mirror with 672 actuators and a high-order pyramid wave-front sensor. During the on-sky commissioning such a system reached performances never achieved before on large ground-based optical telescopes. Images with 40mas resolution and Strehl Ratios higher than 80% have been acquired in H band (1.6 μm). Such images showed a contrast as high as 10^-4. Based on these results, we compare the performances offered by a Natural Guide Star (NGS) system upgraded with the state-of-the-art technology and those delivered by existing Laser Guide Star (LGS) systems. The comparison, in terms of sky coverage and performances, suggests rethinking the current role ascribed to NGS and LGS in the next generation of AO systems for the 8-10 meter class telescopes and Extremely Large Telescopes (ELTs).

Exoplanet imaging is driving a race to higher contrast imaging, both from earth and from space. Next-generation instruments such as the Gemini Planet Imager (GPI) and SPHERE are designed to achieve contrast ratios of 10^-6 - 10^-7 this requires very good wavefront correction and coronagraphic control of diffraction. GPI is a facility instrument, now in integration and test, with first light on the 8-m Gemini South telescope expected by the middle of 2012. It combines a 1700 subaperture AO system using a MEMS deformable mirror, an apodized-pupil Lyot coronagraph, a high-accuracy IR interferometric wavefront calibration system, and a nearinfrared integral field spectrograph to allow detection and characterization of self-luminous extrasolar planets at planet/star contrast ratios of 10^-7. In this paper we will discuss the status of the integration and test now taking place at the University of Santa Cruz California.

The Alignment and Phasing System (APS) is one of the key parts of the Thirty Meter Telescope (TMT) active optics system, with the responsibility for evaluating and correcting the pre-adaptive optics wavefront delivered by the telescope. APS is a high complexity system comprising a multi-channel wavefront-sensing instrument that produces as many as 250,000 discrete measurements and control software that delivers commands to about 12,000 active optics system actuators. The APS software is designed to guide the instrument development and predict its performance via simulation and also ultimately to serve the physical instrument itself. The software is built around a modeling tool we have developed called TMTracer, which is tailored to the optical alignment of extremely large segmented telescopes. We will present the underlying philosophy of TMTracer, as well as its architecture and sample simulation results that demonstrate its capabilities.

TNO is developing the Optical Tube Asssemblies (OTAs) for the ESO VLT Four Laser Guide Star Facility. The OTAs are Galilean 20x beam expanders, expanding a Ø15 mm input beam to a steerable Ø300 mm output beam with a wavefront quality requirement of 50 nm rms. The allowed defocus under the influence of the changing environmental air temperature (0-15°C, -0.7°C/hr gradient) is only 0.2 waves. The thermal behaviour of the system has been analyzed by combining optical, lumped mass and FE analyses. A design that is passively athermalized over a large temperature range as well as under the influence of thermal gradients has been developed. Extensive thermal testing has shown the system performs as required. This paper describes the design and test results.

In this paper we present the current status of control algorithm development for the Thirty Meter Telescope (TMT) Alignment and Phasing System (APS).We discuss ways to address the main challenges inherent in the active control of extremely large segmented telescopes: high complexity of the control problem, disentangling the aberrations on the primary, secondary and tertiary mirrors, and the tight requirements for residual errors. We also present preliminary APS performance estimates derived from simulations. In particular, our simulations show that the tomographic aberration disentanglement is only marginally useful for TMT alignment.

Laser tomography capability using a multi laser guide star (LGS) system is being implemented at the 6.5 m MMT telescope on Mt. Hopkins, AZ. The system uses five range-gated and dynamically refocused Rayleigh laser beacons to sense the atmospheric wavefront aberration. Corrections are then applied to the wavefront using the 336-actuator adaptive secondary mirror of the telescope. So far, the system has demonstrated successful control of ground-layer aberration over a field of view substantially wider than is delivered by conventional adaptive optics. In this paper, we report the latest results from this mode of operation, using for the first time a plate scale on our IR science camera that samples the diffraction scale at the Nyquist limit. We also discuss findings for a reduction in the width of the on-axis point-spread function from 1.07" to <0.2" in H band and present the progress achieved toward the implementation of laser tomography. This will be attempted by means of a least squares reconstructor, which is obtained using simultaneous measurements of the wavefronts from the LGS and an additional natural guide star.

The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) system uses advanced coronagraphic technique for high contrast imaging of exoplanets and disks as close as 1 lambda/D from the host star. In addition to unusual optics, achieving high contrast at this small angular separation requires a wavefront sensing and control architecture which is optimized for exquisite control and calibration of low order aberrations. The SCExAO system was thus designed to include the wavefront sensors required for bias-free high sensitivity and high speed wavefront measurements. Information is combined from two infrared wavefront sensors and a fast visible wavefront sensors to drive a single MEMS type deformable mirror mounted on a tip-tilt mount. The wavefront sensing and control architecture is highly integrated with the coronagraph system.

In this paper we explain why a non-linear curvature wavefront sensor (nlCWFS) is more sensitive than conventional wavefront sensors such as the Shack Hartmann wavefront sensor (SHWFS) and the conventional curvature wavefront sensor (cCWFS) for sensing m_V < 14 natural guide stars. The non-linear approach builds on the successful curvature wavefront sensing concept but uses a non-linear Gerchberg-Saxton (GS) phase diversity algorithm to reconstruct the wavefront. The nonlinear reconstruction algorithm is an advantage for sensitivity but a challenge for fast computation. The current speed is a factor of 10 to 100 times slower than needed for high performance groundbased AO. We present a two step strategy to increase the speed of the algorithm. In the last paper³ we presented laboratory results obtained with a monochromatic source, here we extend our experiment to incorporate a broadband source. The sensitivity of the nlCWFS depends on the ability to extract wavefront phase from diffraction limited speckles therefore it is essential that the speckles do not suffer from chromatic aberration when used with a polychromatic source. We discuss the design for the chromatic re-imaging optics, which through chromatic compensation, allow us to obtain diffraction limited speckles in Fresnel propagated planes on either side of the pupil plane.

Since the realization of the twin Keck telescopes of 10-meter diameter built atop the Mauna Kea in Hawaii, the technology of segmented mirrors has become a cornerstone for on-going projects of Extremely Large Telescopes (ELT). Here the individual mirror segments should actually be phased together (i.e. reconstruct the surface of an ideal continuous, giant mirror) within accuracies typically better than one tenth of the operating wavelength. This could be achieved using existing Wavefront Sensors (WFS), but may also involve the development of alternative methods: in this communication is described a new generation WFS operating in the image plane and able to sense differential piston errors of the segments with residual uncertainties inferior to 25 nm by means of a phase-shifting technique. We describe the principle of the method in both monochromatic and polychromatic light and present its achievable performance in terms of limiting magnitude of the guide star in presence of various noise sources. It is emphasized that the technique is also applicable for co-phasing sparse aperture interferometers, or more generally to any Adaptive Optics (AO) system making use of image plane WFS evaluating telescope wavefront errors (WFE) in real time.

The Giant Magellan Telescope (GMT) will place seven primary mirror segments of 8.4 m diameter on a common mount to form a single co-phased aperture of 25 m. ¹High order adaptive optics (AO) using an adaptive secondary mirror that is segmented in the same way as the primary will correct the telescope's imaging to the diffraction limit in the near infrared. ²Critical to the performance of the telescope will be real-time correction of atmospherically-induced optical path differences between the primary mirror segments. Measuring these errors is challenging because of the large gaps between the segments, where the aberrated wavefront is not explicitly measured by the AO sensors, which are approximately 30 cm even at their narrowest points. In this paper we show that it will be feasible to estimate the path differences between the segments from the commands sent to the adaptive secondary mirror while the AO is running in closed loop. These commands will be an approximate representation of the open-loop atmospheric wavefronts. We have investigated the value of the approach with real-time closed-loop deformable mirror command data from the first-light AO system now running on the Large Binocular Telescope (LBT). ^3,4The data are of very high quality and realistically capture the spatio-temporal behavior of the wavefront. We use data from two nights to show that the GMT segment pathlength errors may be recovered to <25 nm accuracy with a simple linear estimator. Additional simulations show similar performance, which, with high-order AO, is quite adequate to maintain high Strehl ratio at near infrared wavelengths.

Carbon-fiber reinforced polymer (CFRP) composite is an attractive material for fabrication of optics due to its high stiffness-to-weight ratio, robustness, zero coefficient of thermal expansion (CTE), and the ability to replicate multiple optics from the same mandrel. We use 8 and 17 cm prototype CFRP thin-shell deformable mirrors to show that residual CTE variation may be addressed with mounted actuators for a variety of mirror sizes. We present measurements of surface quality at a range of temperatures characteristic of mountaintop observatories. For the 8 cm piece, the figure error of the Al-coated reflective surface under best actuator correction is ~43 nm RMS. The 8 cm mirror has a low surface error internal to the outer ring of actuators (17 nm RMS at 20°C and 33 nm RMS at -5°C). Surface roughness is low (< 3 nm P-V) at a variety of temperatures. We present new figure quality measurements of the larger 17 cm mirror, showing that the intra-actuator figure error internal to the outer ring of actuators (38 nm RMS surface with one-third the actuator density of the 8 cm mirror) does not scale sharply with mirror diameter.

While the concept of wavefront decomposition is a foundation of active optics systems, the choice of basis functions for mirror figure control is divided. The common functions are Zernike polynomials, ubiquitously used for wavefront descriptions, and bending (also called minimum energy or vibration) modes which offer optimal performance. We present a look at the comparative performance between the two approaches, and discuss an implementation approach which seeks to combine much of the analytic and interface simplicity of Zernike polynomials with the improved performance of bending modes.

Variation in density structure and altitude of mesospheric sodium impacts the performance of Adaptive Optics (AO). With large entrance apertures, Laser Guide Stars (LGS) are seen as cylinders with an intensity structure that reflects the density structure of the sodium layers. Such elongation spreads the sodium light over more WaveFront Sensor (WFS) pixels and reduces the signal to noise ratios. This effect is proportional to the square of the telescope diameter: 30 m for TMT and 42 m for E-ELT. NA variability is examined and the resulting elongation analyzed for impact on WaveFront Error. TMT and E-ELT will be compared for methods being applied to mitigate LGS elongation to reduce resulting WaveFront Error.

Wavefront sensors, which use solid-state CCD or CMOS photosensors, are sources of errors in adaptive optic systems. Inaccuracy in the detection of wavefront distortions introduces considerable errors into wavefront reconstruction and leads to overall performance degradation of the adaptive optics system. The accuracy of wavefront sensors is significantly affected by photosensor noise. Thus, it is crucial to formulate high-level photosensor models that enable adaptive optic engineers to simulate realistic effects of noise from wavefront sensors. However, the complexity of solid-state photosensors and multiple noise sources makes it difficult to formulate an adequate model of the photosensor. Moreover, the characterisation of the simulated sensor and comparison with real hardware is often incomplete due to lack of comprehensive standards and guidelines. Owe to these difficulties, engineers work with oversimplified models of the wavefront sensors and consequently have imprecise numerical simulation results. The paper presents an approach for the modelling of noise sources for CCD and CMOS sensors that are used for wavefront sensing in adaptive optics. Both dark and light noise such as fixed pattern noise, photon shot noise, and read noises, as well as, charge-to-voltage noises are described. Procedures for characterisation of both light and dark noises of the simulated photosensors are provided. Numerical simulation results of a photosensor for a high-frame rate Shack-Hartmann wavefront sensor are presented.

A Shack-Hartmann (SH) wavefront sensor (WFS) is used in most modern adaptive optics systems where precision and robustness of centroiding are important issues. The accuracy of the SH WFS depends not only on lenslet quality but also on the measurement accuracy of centroids, especially in low-light conditions. In turn, accuracy depends on light and dark noises that are inevitably present in solid-state photosensors. Using a comprehensive mathematical model of the CMOS photosensor, the accuracy of the Shack-Hartmann wavefront sensor is assessed and analysed for each type of noise. In this paper, new results regarding the influence of different noise sources from a CMOS photosensor on centroiding in Shack-Hartmann wavefront sensors are presented. For the numerical simulations, a comprehensive mathematical model of photosensor's noise was formulated. The influences of light and dark noises as well as pixelisation factor have been assessed. Analysis of the wavefront sensor's accuracy is provided. Results should be of interest for further development of cost-effective wavefront sensors.

Large sky area multi-object fiber spectroscopy telescope (LAMOST) is an innovative reflecting Schmidt telescope. One of its key technology is 4000 dual rotational fiber robot located in the focal plane. This article analyzes the calibration requirements of the 4000 fiber robot. And then, proposes a fast calibration method in the complex field environment, and discribes the specific process how to obtain positioning parameters of the fiber robot rapidly.

High powered guide star laser beams are a potential hazard for aircraft. Currently at the MMT telescope located on Mt. Hopkins in Southern Arizona, five Rayleigh guide stars create a total of 25 W of power at 532 nm wavelength. The ARGOS laser guide star for the Large Binocular Telescope (LBT) located on Mt. Graham in Southern Arizona will generate six Rayleigh guide stars with a total of 108 W at 532 nm. We present an automated system for use at the MMT and the LBT designed to detect aircraft and shutter the lasers when aircraft illumination is pending. The detection system at the MMT uses a single wide-angle CCD camera mounted to the optical support structure of the telescope. The LBT system employs two of the same CCD cameras, and an additional bore-sighted thermal infrared camera. The visible cameras integrate frames for 0.5 s to produce streaks from anti-collision beacons required for all aircraft. The IR camera serves as a backup and to protect unlighted aircraft. In each case, adjacent frames are compared using image processing software to detect streaks and movement in the field. If an aircraft is detected, the position and projected trajectory are calculated and compared to the position of the laser beams. If an aircraft illumination appears likely, the laser safety shutter is closed and a message is sent to the laser operator. As a safety precaution, a heartbeat signal from the control computer is required to keep the laser shutter open.

ARGOS, the laser-guided adaptive optics system for the Large Binocular Telescope (LBT), is now under construction at the telescope. By correcting atmospheric turbulence close to the telescope, the system is designed to deliver high resolution near infrared images over a field of 4 arc minute diameter. Each side of the LBT is being equipped with three Rayleigh laser guide stars derived from six 18 W pulsed green lasers and projected into two triangular constellations matching the size of the corrected field. The returning light is to be detected by wavefront sensors that are range gated within the seeing-limited depth of focus of the telescope. Wavefront correction will be introduced by the telescope's deformable secondary mirrors driven on the basis of the average wavefront errors computed from the respective guide star constellation. Measured atmospheric turbulence profiles from the site lead us to expect that by compensating the ground-layer turbulence, ARGOS will deliver median image quality of about 0.2 arc sec across the JHK bands. This will be exploited by a pair of multi-object near-IR spectrographs, LUCIFER1 and LUCIFER2, with 4 arc minute field already operating on the telescope. In future, ARGOS will also feed two interferometric imaging instruments, the LBT Interferometer operating in the thermal infrared, and LINC-NIRVANA, operating at visible and near infrared wavelengths. Together, these instruments will offer very broad spectral coverage at the diffraction limit of the LBT's combined aperture, 23 m in size.