Marcos Van Dam - Academia.edu (original) (raw)

Papers by Marcos Van Dam

Research paper thumbnail of Keck Adaptive Optics Note 425 Influence of moon light on tip-tilt sensing accuracy using STRAP

AO observations performed in the vicinity of the moon lead to significant background on the STRAP... more AO observations performed in the vicinity of the moon lead to significant background on the STRAP tip/tilt wave front sensor and hence severe drawbacks in terms sensing accuracy of a tip/tilt star. By analyzing all suitable LGS data sets from Jan 2006 to Oct 2006, we evaluated the amount of background photons detected with STRAP as a function of radial distance to the Moon. Moreover we estimated their impact in tip/tilt sensing capability and resulting limiting magnitudes of the tip/tilt guide stars. While for distances < 25 degrees we report a loss of limiting magnitude up to 2 magnitudes for distances > 25 degrees the impact of the moon is negligible (assuming no cirrus clouds).

Research paper thumbnail of Wave-front sensing for adaptive optics in astronomy

Research paper thumbnail of Effect of aperture subdivision on wavefront sensing

Proceedings of SPIE - The International Society for Optical Engineering

ABSTRACT

Research paper thumbnail of Wave-front sensing for adaptive optics in astronomy : a thesis presented for the degree of Doctor of Philosophy, University of Canterbury /

Research paper thumbnail of Geometric wave-front sensing

Estimating the wavefront distortion introduced by the atmosphere is a critical component in corre... more Estimating the wavefront distortion introduced by the atmosphere is a critical component in correcting atmospheric effects in ground based telescopes. Shack-Hartmann and curvature sensors represent the most common methods of wavefront sensing, and we show how they can be analysed using a common framework. This analysis enables us to assess the relative performance as well as develop new hybrid sensing systems.

Research paper thumbnail of GRB 071003: infrared photometry with Keck adaptive optics

Research paper thumbnail of “Earth Research” 3-Dimensional Geological Modelling of Geothermal Systems in New Zealand–a New Visualisation Tool

Diagrammatic 2D representation (i.e., cross-sections and maps) of drillhole data (e.g. stratigrap... more Diagrammatic 2D representation (i.e., cross-sections and maps) of drillhole data (e.g. stratigraphy, permeable zones, secondary mineral occurrence) and inferences (e.g. hydrology, structural relations) have historically been used for visualisation. Advances have been made using newly developed 3D computer modeling software where we are able to render detailed geological information (e.g., stratigraphy, structure, hydrothermal alteration mineralogy) and overlay it with hydrological data (e.g., temperature, flow data). This provides greater insights into active fluid flow behaviour in the geothermal reservoir, and the thermal and chemical evolution of the geothermal system, leading to greater efficiency in the decision-making processes at all stages of field exploration, reservoir development and production.

Research paper thumbnail of Aberrations induced by side-projected laser guide stars in laser tomography adaptive optics systems

Research paper thumbnail of Design of the Laser Tomography Adaptive Optics System for the Giant Magellan Telescope

Research paper thumbnail of First Image of the Dark Side of the Rings of Uranus

The rings of Uranus are oriented edge-on to Earth in 2007 for the first time since their 1977 dis... more The rings of Uranus are oriented edge-on to Earth in 2007 for the first time since their 1977 discovery. The event provided a rare opportunity to observe their dark (unlit) side, where dense rings darkened to near invisibility, but faint rings became much brighter. We present a ground-based infrared image of the unlit side of the rings that shows that the system has changed dramatically since previous views. A broad cloud of faint material permeates the system but is not correlated with the well-known narrow rings or with the embedded dust belts imaged by the Voyager spacecraft. Although some differences can be explained by the unusual viewing angle, we conclude that the dust distribution within the system has changed substantially since the 1986 Voyager encounter and that it occurs on much larger scales than has been seen in other planetary systems. This work was funded by NSF and the Technology Center for Adaptive Optics, managed by UCSC under cooperative agreement no. AST-9876783. The Keck Observatory is operated as a scientific partnership among Caltech, UC, and NASA. Further support was provided by NASA grants NNX06AD12G and NNG06GI25G (HBH), NNX07AK70G (IdP), and NNX06AB98G (MRS).

Research paper thumbnail of Simulating Astronomical Adaptive Optics Systems Using Yao

Adaptive Optics systems are at the heart of the coming Extremely Large Telescopes generation. Giv... more Adaptive Optics systems are at the heart of the coming Extremely Large Telescopes generation. Given the importance, complexity and required advances of these systems, being able to simulate them faithfully is key to their success, and thus to the success of the ELTs. The type of systems envisioned to be built for the ELTs cover most of the AO breeds, from NGS AO to multiple guide star Ground Layer, Laser Tomography and Multi-Conjugate AO systems, with typically a few thousand actuators. This represents a large step up from the current generation of AO systems, and accordingly a challenge for existing AO simulation packages. This is especially true as, in the past years, computer power has not been following Moore's law in its most common understanding; CPU clocks are hovering at about 3GHz. Although the use of super computers is a possible solution to run these simulations, being able to use smaller machines has obvious advantages: cost, access, environmental issues. By using op...

Research paper thumbnail of PULSE: Palomar Ultraviolet Laser for the Study of Exoplanets

PULSE is a new concept to augment the currently operating 5.1-m Hale PALM-3000 exoplanet adaptive... more PULSE is a new concept to augment the currently operating 5.1-m Hale PALM-3000 exoplanet adaptive optics system with an ultraviolet Rayleigh laser and associated wavefront sensor. By using an ultraviolet laser to measure the high spatial and temporal order turbulence near the telescope aperture, where it dominates, one can extend the faintness limit of natural guide stars needed by PALM-3000. Initial simulations indicate that very-high infrared contrast ratios and good visible-light adaptive optics performance will be achieved by such an upgraded system on stars as faint as mV = 16-17 using an optimized low-order NGS sensor. This will enable direct imaging searches for, and subsequent characterization of, companions around cool, low-mass stars for the first time, as well as routine visible-light imaging twice as sharp as HST for fainter targets. PULSE will reuse the laser and wavefront sensor technologies developed for the automated Robo-AO laser system currently operating at the Pa...

Research paper thumbnail of Performance of the Keck II AO system

Research paper thumbnail of Wavefront Reconstruction for a Natural Guide Star Ground Layer Adaptive Optics System on the Giant Magellan Telescope

ABSTRACT In this paper, we present a wavefront reconstruction paradigm for NGS GLAO systems. The ... more ABSTRACT In this paper, we present a wavefront reconstruction paradigm for NGS GLAO systems. The conventional approach to reconstructing the wavefront for LGS GLAO systems is to have a number of LGSs in a ring outside the science field and simply average the individual wavefronts. This approach is not well-suited to NGS GLAO because the stars have an irregular distribution and varying magnitudes. In this paper, we derive covariance matrices for the wavefronts in different directions and the measurement noise. Using these covariance matrices, we are able to find the minimum-variance reconstructor and estimate the residual wavefront as a function of location in the field. This can be used to determine which guide stars produce the best correction. End-to-end simulations in YAO are run to estimate the expected performance of the NGS GLAO system for the Giant Magellan Telescope. We find that there is essentially full sky coverage.

Research paper thumbnail of GMT AO system requirements and error budgets in the preliminary design phase

Adaptive Optics Systems III, 2012

ABSTRACT Error budgets are an indispensable tool for assuring that project requirements can be an... more ABSTRACT 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 ...

Research paper thumbnail of <title>Comparison of tip-tilt controllers using the STRAP wavefront sensor in the W.M. Keck Observatory laser guide star adaptive optics system</title>

Advances in Adaptive Optics II, 2006

The W. M. Keck Observatory adaptive optics (AO) system uses the STRAP wavefront sensor to sense t... more The W. M. Keck Observatory adaptive optics (AO) system uses the STRAP wavefront sensor to sense tip-tilt using a natural guidestar. The higher-order wavefront sensing can be done using light from either a laser guidestar (LGS) or a natural guidestar (NGS). The tip-tilt guidestar can be as bright as 10 th or as faint as 19 th magnitude. In both cases, as high a control bandwidth as possible is desired. Thus, it is of interest to determine the potential of various control algorithms over a wide range of signal-to-noise ratios (SNRs). This paper compares two control algorithms using a set of tip-tilt data taken with the STRAP wavefront sensor (a set of four avalanche diodes arranged as a quad cell). The two algorithms are the standard integral control and a minimum variance (LQG) control designed using the power spectral density (PSD) of the data. The bandwidths of the integral control and the minimum variance control are adjusted to produce the least RMS residual wavefront error. The controllers are compared for SNRs representative of the expected range of guidestars. *

Research paper thumbnail of <title>Upgrading the Keck AO wavefront controllers</title>

Adaptive Optics Systems, 2008

This paper describes the recent upgrade performed on the W. M. Keck Observatory Adaptive Optics (... more This paper describes the recent upgrade performed on the W. M. Keck Observatory Adaptive Optics (AO) systems, in which the wavefront sensors and wavefront controllers were replaced with components based on new technology. The performance of the upgraded system has yielded an increase in limiting guide star magnitude, an increased Strehl ratio for both Laser Guide Star (LGS) and Natural Guide Star (NGS) modes, and has significantly improved reliability and maintainability compared to the original system. Moreover, the controller is scalable, allowing for future upgrades and improvements as needed. We present an overview of the project; describe the basic architecture of the new wavefront sensor and controller; discuss some of the unique features of the system, including the closed loop mirror positioning system, custom wavefront sensor optics, and full-frame-rate telemetry server; and conclude with results from engineering and science tests of the new controller on the Keck II AO system.

Research paper thumbnail of <title>Is that really your Strehl ratio?</title>

Advancements in Adaptive Optics, 2004

Strehi ratio is the most commonly used metric for adaptive optics (AO) performance. It is also th... more Strehi ratio is the most commonly used metric for adaptive optics (AO) performance. It is also the most misused metric. Every Strehl ratio measurement algorithm has subtle differences that result in different measured values. This creates problems when comparing different measurements of the same AO system and even more problems when trying to compare results from different systems.

Research paper thumbnail of Predictive Fourier Wavefront Control: Theory and Observational Results

Frontiers in Optics 2009/Laser Science XXV/Fall 2009 OSA Optics & Photonics Technical Digest, 2009

ABSTRACT

Research paper thumbnail of System Performance Characterization

Principles, Practices, Design, and Applications, 2005

ABSTRACT

Research paper thumbnail of Keck Adaptive Optics Note 425 Influence of moon light on tip-tilt sensing accuracy using STRAP

AO observations performed in the vicinity of the moon lead to significant background on the STRAP... more AO observations performed in the vicinity of the moon lead to significant background on the STRAP tip/tilt wave front sensor and hence severe drawbacks in terms sensing accuracy of a tip/tilt star. By analyzing all suitable LGS data sets from Jan 2006 to Oct 2006, we evaluated the amount of background photons detected with STRAP as a function of radial distance to the Moon. Moreover we estimated their impact in tip/tilt sensing capability and resulting limiting magnitudes of the tip/tilt guide stars. While for distances < 25 degrees we report a loss of limiting magnitude up to 2 magnitudes for distances > 25 degrees the impact of the moon is negligible (assuming no cirrus clouds).

Research paper thumbnail of Wave-front sensing for adaptive optics in astronomy

Research paper thumbnail of Effect of aperture subdivision on wavefront sensing

Proceedings of SPIE - The International Society for Optical Engineering

ABSTRACT

Research paper thumbnail of Wave-front sensing for adaptive optics in astronomy : a thesis presented for the degree of Doctor of Philosophy, University of Canterbury /

Research paper thumbnail of Geometric wave-front sensing

Estimating the wavefront distortion introduced by the atmosphere is a critical component in corre... more Estimating the wavefront distortion introduced by the atmosphere is a critical component in correcting atmospheric effects in ground based telescopes. Shack-Hartmann and curvature sensors represent the most common methods of wavefront sensing, and we show how they can be analysed using a common framework. This analysis enables us to assess the relative performance as well as develop new hybrid sensing systems.

Research paper thumbnail of GRB 071003: infrared photometry with Keck adaptive optics

Research paper thumbnail of “Earth Research” 3-Dimensional Geological Modelling of Geothermal Systems in New Zealand–a New Visualisation Tool

Diagrammatic 2D representation (i.e., cross-sections and maps) of drillhole data (e.g. stratigrap... more Diagrammatic 2D representation (i.e., cross-sections and maps) of drillhole data (e.g. stratigraphy, permeable zones, secondary mineral occurrence) and inferences (e.g. hydrology, structural relations) have historically been used for visualisation. Advances have been made using newly developed 3D computer modeling software where we are able to render detailed geological information (e.g., stratigraphy, structure, hydrothermal alteration mineralogy) and overlay it with hydrological data (e.g., temperature, flow data). This provides greater insights into active fluid flow behaviour in the geothermal reservoir, and the thermal and chemical evolution of the geothermal system, leading to greater efficiency in the decision-making processes at all stages of field exploration, reservoir development and production.

Research paper thumbnail of Aberrations induced by side-projected laser guide stars in laser tomography adaptive optics systems

Research paper thumbnail of Design of the Laser Tomography Adaptive Optics System for the Giant Magellan Telescope

Research paper thumbnail of First Image of the Dark Side of the Rings of Uranus

The rings of Uranus are oriented edge-on to Earth in 2007 for the first time since their 1977 dis... more The rings of Uranus are oriented edge-on to Earth in 2007 for the first time since their 1977 discovery. The event provided a rare opportunity to observe their dark (unlit) side, where dense rings darkened to near invisibility, but faint rings became much brighter. We present a ground-based infrared image of the unlit side of the rings that shows that the system has changed dramatically since previous views. A broad cloud of faint material permeates the system but is not correlated with the well-known narrow rings or with the embedded dust belts imaged by the Voyager spacecraft. Although some differences can be explained by the unusual viewing angle, we conclude that the dust distribution within the system has changed substantially since the 1986 Voyager encounter and that it occurs on much larger scales than has been seen in other planetary systems. This work was funded by NSF and the Technology Center for Adaptive Optics, managed by UCSC under cooperative agreement no. AST-9876783. The Keck Observatory is operated as a scientific partnership among Caltech, UC, and NASA. Further support was provided by NASA grants NNX06AD12G and NNG06GI25G (HBH), NNX07AK70G (IdP), and NNX06AB98G (MRS).

Research paper thumbnail of Simulating Astronomical Adaptive Optics Systems Using Yao

Adaptive Optics systems are at the heart of the coming Extremely Large Telescopes generation. Giv... more Adaptive Optics systems are at the heart of the coming Extremely Large Telescopes generation. Given the importance, complexity and required advances of these systems, being able to simulate them faithfully is key to their success, and thus to the success of the ELTs. The type of systems envisioned to be built for the ELTs cover most of the AO breeds, from NGS AO to multiple guide star Ground Layer, Laser Tomography and Multi-Conjugate AO systems, with typically a few thousand actuators. This represents a large step up from the current generation of AO systems, and accordingly a challenge for existing AO simulation packages. This is especially true as, in the past years, computer power has not been following Moore's law in its most common understanding; CPU clocks are hovering at about 3GHz. Although the use of super computers is a possible solution to run these simulations, being able to use smaller machines has obvious advantages: cost, access, environmental issues. By using op...

Research paper thumbnail of PULSE: Palomar Ultraviolet Laser for the Study of Exoplanets

PULSE is a new concept to augment the currently operating 5.1-m Hale PALM-3000 exoplanet adaptive... more PULSE is a new concept to augment the currently operating 5.1-m Hale PALM-3000 exoplanet adaptive optics system with an ultraviolet Rayleigh laser and associated wavefront sensor. By using an ultraviolet laser to measure the high spatial and temporal order turbulence near the telescope aperture, where it dominates, one can extend the faintness limit of natural guide stars needed by PALM-3000. Initial simulations indicate that very-high infrared contrast ratios and good visible-light adaptive optics performance will be achieved by such an upgraded system on stars as faint as mV = 16-17 using an optimized low-order NGS sensor. This will enable direct imaging searches for, and subsequent characterization of, companions around cool, low-mass stars for the first time, as well as routine visible-light imaging twice as sharp as HST for fainter targets. PULSE will reuse the laser and wavefront sensor technologies developed for the automated Robo-AO laser system currently operating at the Pa...

Research paper thumbnail of Performance of the Keck II AO system

Research paper thumbnail of Wavefront Reconstruction for a Natural Guide Star Ground Layer Adaptive Optics System on the Giant Magellan Telescope

ABSTRACT In this paper, we present a wavefront reconstruction paradigm for NGS GLAO systems. The ... more ABSTRACT In this paper, we present a wavefront reconstruction paradigm for NGS GLAO systems. The conventional approach to reconstructing the wavefront for LGS GLAO systems is to have a number of LGSs in a ring outside the science field and simply average the individual wavefronts. This approach is not well-suited to NGS GLAO because the stars have an irregular distribution and varying magnitudes. In this paper, we derive covariance matrices for the wavefronts in different directions and the measurement noise. Using these covariance matrices, we are able to find the minimum-variance reconstructor and estimate the residual wavefront as a function of location in the field. This can be used to determine which guide stars produce the best correction. End-to-end simulations in YAO are run to estimate the expected performance of the NGS GLAO system for the Giant Magellan Telescope. We find that there is essentially full sky coverage.

Research paper thumbnail of GMT AO system requirements and error budgets in the preliminary design phase

Adaptive Optics Systems III, 2012

ABSTRACT Error budgets are an indispensable tool for assuring that project requirements can be an... more ABSTRACT 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 ...

Research paper thumbnail of <title>Comparison of tip-tilt controllers using the STRAP wavefront sensor in the W.M. Keck Observatory laser guide star adaptive optics system</title>

Advances in Adaptive Optics II, 2006

The W. M. Keck Observatory adaptive optics (AO) system uses the STRAP wavefront sensor to sense t... more The W. M. Keck Observatory adaptive optics (AO) system uses the STRAP wavefront sensor to sense tip-tilt using a natural guidestar. The higher-order wavefront sensing can be done using light from either a laser guidestar (LGS) or a natural guidestar (NGS). The tip-tilt guidestar can be as bright as 10 th or as faint as 19 th magnitude. In both cases, as high a control bandwidth as possible is desired. Thus, it is of interest to determine the potential of various control algorithms over a wide range of signal-to-noise ratios (SNRs). This paper compares two control algorithms using a set of tip-tilt data taken with the STRAP wavefront sensor (a set of four avalanche diodes arranged as a quad cell). The two algorithms are the standard integral control and a minimum variance (LQG) control designed using the power spectral density (PSD) of the data. The bandwidths of the integral control and the minimum variance control are adjusted to produce the least RMS residual wavefront error. The controllers are compared for SNRs representative of the expected range of guidestars. *

Research paper thumbnail of <title>Upgrading the Keck AO wavefront controllers</title>

Adaptive Optics Systems, 2008

This paper describes the recent upgrade performed on the W. M. Keck Observatory Adaptive Optics (... more This paper describes the recent upgrade performed on the W. M. Keck Observatory Adaptive Optics (AO) systems, in which the wavefront sensors and wavefront controllers were replaced with components based on new technology. The performance of the upgraded system has yielded an increase in limiting guide star magnitude, an increased Strehl ratio for both Laser Guide Star (LGS) and Natural Guide Star (NGS) modes, and has significantly improved reliability and maintainability compared to the original system. Moreover, the controller is scalable, allowing for future upgrades and improvements as needed. We present an overview of the project; describe the basic architecture of the new wavefront sensor and controller; discuss some of the unique features of the system, including the closed loop mirror positioning system, custom wavefront sensor optics, and full-frame-rate telemetry server; and conclude with results from engineering and science tests of the new controller on the Keck II AO system.

Research paper thumbnail of <title>Is that really your Strehl ratio?</title>

Advancements in Adaptive Optics, 2004

Strehi ratio is the most commonly used metric for adaptive optics (AO) performance. It is also th... more Strehi ratio is the most commonly used metric for adaptive optics (AO) performance. It is also the most misused metric. Every Strehl ratio measurement algorithm has subtle differences that result in different measured values. This creates problems when comparing different measurements of the same AO system and even more problems when trying to compare results from different systems.

Research paper thumbnail of Predictive Fourier Wavefront Control: Theory and Observational Results

Frontiers in Optics 2009/Laser Science XXV/Fall 2009 OSA Optics & Photonics Technical Digest, 2009

ABSTRACT

Research paper thumbnail of System Performance Characterization

Principles, Practices, Design, and Applications, 2005

ABSTRACT