1,721,190 research outputs found
Adaptive optics with an infrared Pyramid wavefront sensor
Full text linkWavefront sensing in the infrared is highly desirable for the study of M-type stars and cool red objects, as they are sufficiently bright in the infrared to be used as the adaptive optics guide star. This aids in high contrast imaging, particularly for low mass stars where the star-to-planet brightness ratio is reduced. Here we discuss the combination of infrared detector technology with the highly sensitive Pyramid wavefront sensor (WFS) for a new generation of systems. Such sensors can extend the capabilities of current telescopes and meet the requirements for future instruments, such as those proposed for the giant segmented mirror telescopes. Here we introduce the infrared Pyramid WFS and discuss the advantages and challenges of this sensor. We present a new infrared Pyramid WFS for Keck, a key sub-system of the Keck Planet Imager and Characterizer (KPIC). The design, integration and testing is reported on, with a focus on the characterization of the SAPHIRA detector used to provide the H-band wavefront sensing. Initial results demonstrate a required effective read noise <1e^– at high gain
Near-infrared wavefront sensing
Full text linkWe discuss the advantages of wavefront sensing at near-infrared (IR) wavelengths with low-noise detector technologies that have recently become available. In this paper, we consider low order sensing with laser guide star (LGS) adaptive optics (AO) and high order sensing with natural guide star (NGS) AO. We then turn to the application of near-IR sensing with the W. M. Keck Observatory (WMKO) AO systems for science and as a demonstrator for similar systems on extremely large telescopes (ELTs). These demonstrations are based upon an LGS AO near-IR tip-tilt-focus sensor and our collaboration to implement a near-IR pyramid wavefront sensor (PWFS) for a NGS AO L-band coronagraphic imaging survey to identify exoplanet candidates
Approximate nonnegative matrix factorization algorithm for the analysis of angular differential imaging data
Full text linkThe angular differential imaging (ADI) is used to improve contrast in high resolution astronomical imaging. An example is the direct imaging of exoplanet in camera fed by Extreme Adaptive Optics. The subtraction of the main dazzling object to observe the faint companion was improved using Principal Component Analysis (PCA). It factorizes the positive astronomical frames into positive and negative components. On the contrary, the Nonnegative Matrix Factorization (NMF) uses only positive components, mimicking the actual composition of the long exposure images
Spatial filtering applied to the pyramid WFS: Simulations and preliminary results
Full text linkIn this paper we discuss the potentiality of the spatial filtering approach for the case of a pupil plane wavefront sensor like the pyramid sensor. Filtering is realized by selectively blocking the light just before the pyramid prism. Several schemes can be followed to accomplish this: from a simple field stop that blocks high-order spatial frequencies in order to reduce the aliasing effect (an example is the so-called spatial filtered Shack- Hartmann) to more complicated frequency-selection schemes. In this work we present the simulation environment that we developed to investigate different approaches in this sense aimed at understanding if any practical advantages in wavefront sensing can be effectively attained in particular regimes. We present some preliminary results obtained with end-to-end simulations. In particular, we qualitavely explored the simplest frequency-selection scheme consisting of a field stop just in front of the pyramid. We show that this can help mitigating the effect of contaminating high-order frequencies. Next steps will be in the direction of exploring different reference star brightness regimes in order to determine under which conditions spatial filtering can improve the quality of closed-loop correction. Moreover, different spatial filter sizes and shapes to control the frequencies conveyed to the wave-front sensor will be investigated
Status of MagAO and review of astronomical science with visible light adaptive optics
Full text linkWe review astronomical results in the visible (λ<1μm) with adaptive optics and note the status the MagAO system and the recent upgrade to visible camera's Simultaneous/Spectra Differential Imager (SDI+) mode. Since mid- 2013 there has been a rapid increase visible AO with over 50 refereed science papers published in just 2015-2016 timeframe. Currently there are productive small (D < 2 m) visible light AO telescopes like the UV-LGS Robo-AO system (Baranec, et al. 2016). The largest (D=8m) telescope to achieve regular visible AO science is SPHERE/ZIMPOL. ZIMPOL is a polarimeter fed by the 1.2 kHz SPHERE ExAO system (Fusco et al. 2016). ZIMPOL's ability to differentiate scattered polarized light from starlight allows the sensitive detection of circumstellar disks, stellar surfaces, and envelopes of evolved AGB stars. The main focus of this paper is another large (D=6.5m Magellan telescope) AO system (MagAO) which has been very productive in the visible as well (particularly at the H-alpha emission line). MagAO is an advanced Adaptive Secondary Mirror (ASM) AO system at the Magellan in Chile. This ASM secondary has 585 actuators with < 1 msec response times (0.7 ms typically). MagAO utilizes a 1 kHz pyramid wavefront sensor (PWFS). The relatively small actuator pitch ( 22 cm/subap, 300 modes, upgraded to 30 pix dia. PWFS) allows moderate Strehls to be obtained in the visible (0.63-1.05 microns). Long exposures (60s) achieve <30mas resolutions and 30% Strehls at 0.62 microns (r') with the VisAO camera (0.5-1.0 μm) in 0.5" seeing with bright R <= 9 mag stars ( 10% Strehls can be obtained on fainter R 12 mag guide stars). Differential Spectral Imaging (SDI) at H-alpha has been very important for accreting exoplanet detection. There is also a 1-5micron science camera (Clio; Morzinski et al. 2016). These capabilities have led to over 35 MagAO refereed science publications. Here we review the key steps to having good performance in the visible and review the exciting new AO visible science opportunities and science results in the fields of: exoplanet detection; circumstellar and protoplanetary disks; young stars; AGB stars; emission line jets; and stellar surfaces. The recent rapid increase in the scientific publications and power of visible AO is due to the maturity of the next-generation of AO systems and our new ability probe circumstellar regions with very high (10-30 mas) spatial resolutions that would otherwise require much larger (<10m) diameter telescopes in the infrared
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Development of a High-Contrast Adaptive Optics Phasing Testbed for the Giant Magellan Telescope
No full textOur galaxy hosts ∼ 300 billion stars. Ever since the first exoplanet was discovered in 1992, over 5,000 more exoplanet discoveries have been confirmed, and the number is still counting. As each new exoplanet is discovered, the case seems more and more likely that each star in our Milky Way galaxy must have at least one exoplanet orbiting around it. Many of these exoplanets also fall into the potentially habitable, terrestrial size category, meaning there could be billions of earth like planets waiting to be discovered. If we hope to discover life outside of our solar system, it has been shown that directly imaging these potentially habitable exoplanets in visible light reflected from its host star is optimal. This is very possible, however difficult, since this requires Extremely Large Telescopes (ELTs; ∼30m in diameter) to achieve high angular resolutions and contrasts, extreme adaptive optics (ExAO) to suppress the effects of atmospheric seeing, and coronagraphy to block the starlight. These three technologies could coexist once the 25.4-m Giant Magellan Telescope (GMT) is completed in 2029. With the combined power of ExAO and the future GMT, the discovery of life outside of our solar system may become a reality. However, the GMT’s unique seven segmented primary mirror design raises a challenge to keep the telescope segments co-phased—a task which is critical for direct imaging of exo-earths and any other diffraction-limited science with the GMT. This dissertation addresses the challenge of co-phasing a giant segmented telescope for exoplanet imaging and describes the development of a High-Contrast Adaptive optics phasing Testbed (HCAT) for the GMT. The testbed simulates the GMT with real optics in a lab environment with six piston, tip, and tilt actuators and tests a working concept for a “parallel deformable mirror” to optically redistribute the GMT pupil onto seven commercially available 3,000 actuator deformable mirrors. HCAT also leverages an existing ExAO system called MagAO-X to test and demonstrate segment phase sensing and AO-control with a real ExAO system. I will first introduce the GMT and the “piston problem.” Then, I will give an introduction to adaptive optics and discuss the design and build of MagAO-X. I will then discuss the development of an early stage GMT proto-testbed which was a simple GMT simulator that provided insight into co-phasing a segmented telescope. This early stage GMT proto-testbed evolved into the official prototype version of HCAT (p-HCAT), which led to the development of a new phasing method for co-phasing the GMT using a novel optic called the “Holographic Dispersed Fringe Sensor” (HDFS). The success of the demonstrations performed with p-HCAT and the novel HDFS are discussed. These results have influenced the GMT to adapt this phasing method as their official designated phase sensor for GMT exoplanet imaging. Finally, the design and build of the full-scale HCAT testbed will be described with a demonstration of the “parallel DM” working in the lab
Dealing with the cigar: Preliminary performance estimation of an INGOT WFS
Full text linkAs LGSs come from an excited cigar-shaped region in the sodium layer, they do not behave as point-like sources, therefore a new class of WFSs has been proposed to account for such elongation: the Ingot WFSs, the LGS-counterpart of a pyramid WFS. As they appear to be very promising, here we summarize the main reasons and goal of such a LGS-dedicated WFS and present the concept behind the code developed to produce numerical simulations, exploring the space of parameters. We report different approaches for the approximation of the extended source and the model adopted for the ingot prism simulation
Optimizing multi-LGS WFS AO performance in the context of sodium profile evolution and non-common path aberration
Full text linkFor Extremely Large Telescope (ELT) adaptive optics (AO) systems, multiple Sodium Laser Guide Star (LGS) wavefront sensors (WFSs) are required to achieve high sky coverage and diffraction limited performance. However, temporal and spatial variation of the sodium profile causes measurement biases that appear at all time scales and vary between LGS WFSs. To make things worse, optical design residuals, polishing and alignment errors also create non-common-path aberrations (NCPA) that vary between sub-apertures and different WFS, causing LGS WFS to work significantly off null with a nonlinear response. The induced aberrations are consequently non-radially symmetric, even for center launch laser beams with polar coordinate detectors. Natural guide star (NGS) based truth wavefront sensors are often suggested as a method of sensing these LGS WFS aberrations, but a single sensor will suffer strong anisoplanatism that may introduce additional errors. In this paper, we present mitigation strategies and performance estimations based on simulations for the Thirty Meter Telescope (TMT) Narrow Field Infrared AO system (NFIRAOS)
Real-Time controller (RTC) for the Narrow Field Infrared Adaptive Optics System (NFIRAOS) for TMT final design
Full text linkThe Real-Time Controller (RTC) for the Thirty Meter Telescope (TMT) Narrow Field Infrared Adaptive Optics System (NFIRAOS) is the software and server hardware that converts wavefront error measurements into wavefront corrector demands, at the heart of the laser guide star multi-conjugate adaptive optics (MCAO) or natural guide star adaptive optics (NGS AO). The RTC takes input from up to six Shack-Hartmann Laser Guide Star wavefront sensors (LGS WFS), one high-order Natural Guide Star Pyramid Wavefront Sensor (PWFS), up to three Shack-Hartmann On-Instrument wavefront sensors (OIWFS) that are located in the client science instruments, and up to 4 on-detector guide windows (ODGW) also in the client instruments. The RTC controls two deformable mirrors conjugated to 0km (DM0) and 11.8km (DM11). DM0 is mounted on a tip/tilt stage (TTS). During the final design phase we performed prototyping to verify that off-the-shelf servers using general purpose CPUs are able to support the maximum 800 Hz frequency at which the RTC is required to operate. We also considered methods to provide live data streams to a graphical user interface without impacting the AO system performance. This paper will discusses the outcome of the impact of jitter and latency on loop speed in our prototype and an overview of the RTC pipeline, including the many “knobs” that can be turned to fine-tune the behavior of NFIRAOS in different observing modes, and under different observing conditions
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