Using Site Testing Data for Adaptive Optics Simulations

SPIE Proceedings, 2010

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.

Advancements in Adaptive Optics, 2004

The scientific return on adaptive optics on large telescopes has generated a new vocabulary of different adaptive optics (AO) modalities. Multiobject AO (MOAO), multiconjugate AO (MCAO), ground-layer AO (GLAO), and extreme contrast AO (ExAO) each require complex new extensions in functional requirements beyond the experience gained with systems operational on large telescopes today. Because of this potential for increased complexity, a more formal requirements development process is recommended. We describe a methodology for requirements definition under consideration and summarize the current scientific prioritization of TMT AO capabilities.

2000

Integrated Modeling of Telescopes, 2002

In this paper we describe the development of a C++ class library for the simulation of adaptive optics systems. This library includes functionality to simulate the propagation of electromagnetic waves through a randomly generated turbulent atmosphere and through an adaptive optical system. It includes support for extended emitters and laser guide stars, and for different types of wavefront sensors and reconstructors. The library also aims to support parallelization of simulations across symmetric multiprocessor and cluster supercomputers.

2006

The Adaptive Optics Facility is a project to convert UT4 into a specialised Adaptive Telescope. The present secondary mirror (M2) will be replaced by a new M2-Unit hosting a 1170-actuator deformable mirror. The three focal stations will be equipped with instruments adapted to the new capability of this UT. Two instruments have been identified for the two Nasmyth foci: Hawk-I with its AO module GRAAL allowing a Ground Layer Adaptive Optics correction and MUSE with GALACSI for GLAO correction and Laser Tomography Adaptive Optics correction. A future instrument still needs to be defined for the Cassegrain focus. Several guide stars are required for the type of adaptive corrections needed and a Four Laser Guide Star Facility (4LGSF) is being developed in the scope of the AO Facility. Convex mirrors like the VLT M2 represent a major challenge for testing and a substantial effort is dedicated to this. ASSIST, is a test bench that will allow testing of the Deformable Secondary Mirror and b...

1994

lbis paper outlines the key results of the Very Large Telescope (VLT) Adaptive Optics System Study perfonned by MMS/UTOS under an ESO contract A conceptual design was developed based entirely on available and demonstrated technologies. Key subsystems included a 250 actuator continuous facesheet Defonnable Mirror, an intensified Shack-Hartmann wavefront sensor and a DSP-based fast processor utilizing a parallel architecture. The

The Naval Prototype Optical Interferometer (NPOI) is a long-baseline, multi-station interferometer whose collection apertures can be relocated to provide flexible baseline lengths. While NPOI has the longest baseline at optical wavelengths in the world, the sensitivity of the interferometer is limited by the size of the individual collection apertures which are currently 0.5 meters in diameter. NPOI is currently upgrading its collection apertures to 1.4 meter diameter light weight telescopes to increase the sensitivity. At its location on the Anderson Mesa in Arizona, the chosen diameter of the telescope apertures is much larger than the average r 0 of the site. As a result, adaptive optics must be used to correct for the wavefront aberrations. Several adaptive optics system configurations are suitable to provide the required wavefront correction, but it is highly desirable to have the adaptive optics systems as a component of the telescopes. This is being accomplished by designing the telescopes so that the adaptive optics system resides in the base of each telescope allowing a truly reconfigurable array. Thus evaluating and characterizing the performance of the adaptive optics systems is a critical component of identifying the desired adaptive optics system to support the move to larger aperture telescopes. This paper outlines a modular, electro-optical testbed that has been constructed for characterizing candidate adaptive optics systems for use at NPOI. The testbed makes use of innovative technologies to characterize the spatial and temporal performance of an adaptive optics system. Spatial performance is evaluated using a spatial light modulator liquid crystal device while temporal response is evaluated with a fast steering mirror that is used in series with the liquid crystal device. We report on the capabilities of the testbed and on the initial characterization of a low cost portable adaptive optics system.

Advances in Adaptive Optics II, 2006

Extreme adaptive optics systems dedicated to the search for extrasolar planets are currently being developed for most 8-10 meter telescopes. Extensive computer simulations have shown the ability of both Shack-Hartmann and pyramid wave front sensors to deliver high Strehl ratio correction expected from extreme adaptive optics but few experiments have been realized so far. The high order test bench implements extreme adaptive optics on the MACAO test bench with realistic telescope conditions reproduced by star and turbulence generators. A 32×32 actuator micro deformable mirror, one pyramid wave front sensor, one Shack-Hartmann wave front sensor, the ESO SPARTA real time computer and an essentially read-noise free electron multiplying CCD60 (E2V CCD60) provide an ideal cocoon to study the different behavior of the two types of wave front sensors in terms of linearity, sensitivity to calibration errors, noise propagation, specific issues to pyramid or Shack-Hartmann wave front sensors, etc. We will describe the overall design of this test bench and will focus on the characterization of two essential subsystems: the micro deformable mirror and the phase screens.

2008

High-contrast imagers dedicated to the search for extrasolar planets are currently being developed for the VLT (SPHERE) and Gemini (GPI) observatories. A vital part of such a high-contrast imager is the extreme adaptive optics (XAO) system that very efficiently removes effects of atmospheric turbulence and instrument aberrations. The high order test bench (HOT) implements an XAO system under realistic telescope conditions reproduced by star and turbulence generators. New technological developments (32x32 actuator micro deformable mirror, read-noise free electron multiplying CCD60, SPARTA real time computer) are used to study and compare two potential XAO wave front sensors: The Pyramid-and the Shack-Hartmann wave front sensors. We will describe the overall design of HOT including the subsystems. We will present the closed loop study results of the behavior of the Shack-Hartmann wave front sensor in terms of linearity, sensitivity to calibration errors, performance and other specific issues.

Proceedings of the International Astronomical Union, 2005

Adaptive Optics (AO) will be essential for accomplishing many, if not most, of the science objectives currently planned for Extremely Large Telescopes including GMT, OWL, and TMT. AO will be needed to support a range of instrumentation, including near infrared (IR) imagers and spectrometers, mid IR imagers and spectrometers, "planet finding" instrumentation and wide-field optical spectrographs. Multiple advanced AO systems, utilizing the full range of concepts currently under development, will need to be combined into an integrated architecture to meet a broad range of requirements for field-of-view, spatial resolution and spectral bandpass. In this paper, we describe several of the possible options for these systems and outline the range of issues, trade studies and component development activities which must be addressed. Some of these challenges include very high-order, large-stroke wavefront correction, tip-tilt sensing with faint natural guide stars to maximize sky coverage, laser guide star wavefront sensing on a very large aperture and achieving extremely high contrast ratios for the detection of extra-solar planet and other faint companions of nearby bright stars.

Adaptive Optics Systems, 2008

Atmospheric turbulence compensation via adaptive optics (AO) will be essential for achieving most objectives of the TMT science case. The performance requirements for the initial implementation of the observatory's facility AO system include diffraction-limited performance in the near IR with 50 per cent sky coverage at the galactic pole. This capability will be achieved via an order 60x60 multi-conjugate AO system (NFIRAOS) with two deformable mirrors optically conjugate to ranges of 0 and 12 km, six high-order wavefront sensors observing laser guide stars in the mesospheric sodium layer, and up to three low-order, IR, natural guide star wavefront sensors located within each client instrument. The associated laser guide star facility (LGSF) will consist of 3 50W class, solid state, sum frequency lasers, conventional beam transport optics, and a launch telescope located behind the TMT secondary mirror.

Advances in Adaptive Optics II, 2006

We arrive at a Ground Layer Adaptive Optics (GLAO) design that offers true seeing-improved performance and operation for the red and infrared wavelengths. The design requires an adaptive secondary (AM2) and that the sodium Laser Guide Star (LGS) launch telescope be able to steer four of the beams to 8.5 arcminutes off-axis. When provided with this, the proposed design is potentially the simplest, lowest cost design that can take the form of an upgrade. This is seen as a significant advantage over designs that would build an adaptive mirror into each of the four arms of WFOS. We show that the performance penalty for using one mirror instead of four to correct the entire 81 square arcminute WFOS field is minor.

Proceedings of SPIE, 2005

Although many of the instruments planned for the TMT (Thirty Meter Telescope) have their own closely-coupled adaptive optics systems, TMT will also have a facility Adaptive Optics (AO) system feeding three instruments on the Nasmyth platform. For this Narrow-Field Infrared Adaptive Optics System, NFIRAOS (pronounced nefarious), the TMT project considered two architectures. One, described in this paper, employs conventional deformable mirrors with large diameters of about 300 mm and this is the reference design adopted by the TMT project. An alternative design based on MEMS was also studied, and is being presented separately in this conference. The requirements for NFIRAOS include 0.8-5 microns wavelength range, 30 arcsecond diameter output field of view (FOV), excellent sky coverage, and diffraction-limited atmospheric turbulence compensation (specified at 133 nm RMS including residual telescope and science instrument errors.) The reference design for NFIRAOS includes multiple sodium laser guide stars over a 70 arcsecond FOV, and an infrared tip/tilt/focus/astigmatism natural guide star sensor within instruments. Larger telescopes require greater deformable mirror (DM) stroke. Although initially NFIRAOS will correct a 10 arcsecond science field, it uses two deformable mirrors in series, partly to provide sufficient stroke for atmospheric correction over the 30 m telescope aperture, but mainly to partially correct a 2 arcminute diameter "technical" field to sharpen near-IR natural guide stars and improve sky coverage. The planned upgrade to full performance includes replacing the groundconjugated DM with a higher actuator density, and using a deformable telescope secondary mirror as a "woofer." NFIRAOS incorporates an instrument rotator and selection of three live instruments: a near-Infrared integral field Imaging spectrograph, a near-infrared echelle spectrograph, and after upgrading NFIRAOS to full multi-conjugation, a wide field (30 arcsecond) infrared camera.

Adaptive Optics Systems II, 2010

Modeling adaptive optics (AO) systems is crucial to understanding their performance and a key aid in their design. The Giant Magellan Telescope (GMT) is planning three AO modes at first light: natural guide star AO, ground-layer AO and laser tomography AO. This paper describes how a modified version of YAO, an open-source general-purpose AO simulation tool written in Yorick, is used to simulate the GMT AO modes. The simulation tool was used to determine the piston segment error for the GMT. In addition, we present a comparison of different turbulence simulation approaches. This paper and another 3 outline the progress made in modeling the GMT AO system using end-to-end simulation tools, and the lessons learned along the journey. The aim of the simulation effort is two-fold: to Further author information: send correspondence to Marcos van Dam, [email protected]

Adaptive Optics Systems, 2008

Atmospheric turbulence compensation via adaptive optics (AO) will be essential for achieving most objectives of the TMT science case. The performance requirements for the initial implementation of the observatory's facility AO system include diffraction-limited performance in the near IR with 50 per cent sky coverage at the galactic pole. This capability will be achieved via an order 60x60 multi-conjugate AO system (NFIRAOS) with two deformable mirrors optically conjugate to ranges of 0 and 12 km, six high-order wavefront sensors observing laser guide stars in the mesospheric sodium layer, and up to three low-order, IR, natural guide star wavefront sensors located within each client instrument. The associated laser guide star facility (LGSF) will consist of 3 50W class, solid state, sum frequency lasers, conventional beam transport optics, and a launch telescope located behind the TMT secondary mirror. In this paper, we report on the progress made in designing, modeling, and validating these systems and their components over the last two years. This includes work on the overall layout and detailed opto-mechanical designs of NFIRAOS and the LGSF; reliable wavefront sensing methods for use with elongated and time-varying sodium laser guide stars; developing and validating a robust tip/tilt control architecture and its components; computationally efficient algorithms for very high order wavefront control; detailed AO system modeling and performance optimization incorporating all of these effects; and a range of supporting lab/field tests and component prototyping activities at TMT partners. Further details may be found in the additional papers on each of the above topics.