The majority of current Adaptive Optics (AO) systems do not compensate properly for vibrations within the optical path. For this reason the mitigation of vibration effects in astronomical AO systems is extremely important. The mechanical vibration effects, acting in the science light propagation path, strongly affect the performance of the LBTO/AO system. A frequency-based analysis of the pyramidal wavefront sensor data (PWFS) and the accelerometers network data (OVMS+) on the telescope structure was done in order to identify the principal mechanical vibration frequencies.
Vibration effects acting in the science light path reduce the performance of the adaptive optics systems (AO). In order to mitigate the vibration effects and to improve the performance of the AO systems, an adequate model for the vibration in necessary. Traditionally, those vibrations are modelled as oscillators (with or without damping) driven by white noise. In this work, we address the identification of a continuous-time oscillator from discrete-time samples of the position. To this end, we use Maximum Likelihood estimation method to estimate the vibrations frequency.
To improve the modeling of seeing and its forecast over Armazones and Paranal, we applied two different C<sup>2</sup><sub>n</sub> methods to estimate the vertical refractive index structure. One method, using temperature, pressure and turbulent kinetic energy (TKE), simulates the planetary boundary layer (PBL) C<sup>2</sup><sub>n</sub> . The second method simulates in the free atmosphere, using temperature, pressure and vertical wind shear. The combination of both methods delivers the whole vertical structure of the C<sup>2</sup><sub>n </sub>from ground level up to the stratosphere, and consequently we can derive the astronomical seeing. These atmospheric variables were calculated using WRF, configured in high temporal and spatial resolution. Our results show that the combination of these two methods gives improved results than when are used separately. We compared our simulations with measured data from MASS and DIMM instruments located at both sites.
In the era of high-angular resolution astronomical instrumentation, where long and very long baseline interferometers (constituted by many, ∼20 or more, telescopes) are expected to work not only in the millimeter and submillimeter domain, but also at near and mid infrared wavelengths (experiments such as the Planet Formation Imager, PFI, see Monnier et al. 2018 for an update on its design); any promising strategy to alleviate the costs of the individual telescopes involved needs to be explored. In a recent collaboration between engineers, experimental physicists and astronomers in Valparaiso, Chile, we are gaining expertise in the production of light carbon fiber polymer reinforced mirrors. The working principle consists in replicating a glass, or other substrate, mandrel surface with the mirrored adequate curvature, surface characteristics and general shape. Once the carbon fiber base has hardened, previous studies have shown that it can be coated (aluminum) using standard coating processes/techniques designed for glass-based mirrors. The resulting surface quality is highly dependent on the temperature and humidity control among other variables. Current efforts are focused on improving the smoothness of the resulting surfaces to meet near/mid infrared specifications, overcoming, among others, possible deteriorations derived from the replication process. In a second step, at the validation and quality control stage, the mirrors are characterized using simple/traditional tools like spherometers (down to micron precision), but also an optical bench with a Shack-Hartman wavefront sensor. This research line is developed in parallel with a more classical glass-based approach, and in both cases we are prototyping at the small scale of few tens of cms. We here present our progress on these two approaches.
Frequency-based analysis and comparisons of tip-tilt on-sky data registered with 6.5 Magellan Telescope Adaptive Optics (MagAO) system on April and Oct 2014 was performed. Twelve tests are conducted under different operation conditions in order to observe the influence of system instrumentation (such as fans, pumps and louvers). Vibration peaks can be detected, power spectral densities (PSDs) are presented to reveal their presence. Instrumentation-induced resonances, close-loop gain and future challenges in vibrations mitigation techniques are discussed.
KEYWORDS: Telescopes, Fluctuations and noise, Data modeling, Sensors, Adaptive optics, Adaptive optics, Control systems, Control systems, Signal processing, Turbulence, Charge-coupled devices, Device simulation
The Magellan Telescope Adaptive Optics System (MagAO) is subject to resonance effects induced by elements within the system instrumentation, such as fans and cooling pumps. Normalized PSDs are obtained through frequency-based analysis of closed-loop on-sky data, detecting and measuring vibration effects. Subsequently, a space-state model for the AO loop is obtained, using a standard AO loop scheme with an integrator-based controller and including the vibration effects as disturbances. Finally, a new control alternative is proposed, focusing on residual phase variance minimization through the design and simulation of an optimal LQG control approach.
Mechanical vibrations affect the performance in modern adaptive optics systems. These structural vibrations induce aberration mainly in tip-tilt modes that reduce the accuracy of the astronomical instrument. Therefore, control actions need to be taken. With this purpose we present a laboratory demonstration of vibration rejection of tip-tilt modes using closed-loop control, inducing vibration on the test bench via an eccentric motor with controllable frequency, in order to simulate the structural vibrations mentioned above. We measure the laser vibration and its tip-tilt aberration using a camera and a Shack Hartmann Wave Front Sensor. The control action is carried out by a Fast Steering Mirror (FSM).
The adaptive optics system performance depends on multiple factors, including the quality of the laser beam before being projected to the mesosphere. Cumbersome procedures are required in the laser system to optimize the laser beam in terms of amplitude and phase. However, aberrations of the laser beam are still detected during the operations. The performance of laser projection systems can be improved compensating the effects of aberrations in the laser source or misalignment in the transfer optics before the laser beam propagating through the aperture. Despite the algorithm previously reported predict effective amplitude and phase correction is strongly dependent of an accurate DM characterization and transfer optics alignments. The use of feedback makes the system response better in presence of modeling error and external disturbances. A 2-DM closed loop approach for amplitude and a phase correction is designed. Finally the results of simulations and comparisons are discussed.
Multiple sodium laser beacons are a crucial development in multi-conjugate adaptive optics systems that offers wide-field diffraction limited adaptive optics correction to the astronomical community. This correction is strongly dependent on the laser beam power and quality, so a beam shaping concept is currently being developed to speed-up calibration and alignment of the laser before every run. A method previously reported, has now been implemented on a laboratory bench using MEMS deformable mirrors. Necessary calibration and characterization of the deformable mirrors are described and the results for experimental amplitude correction are presented.
The main telescope of the UC Observatory Santa Martina is a 50cm optical telescope donated by ESO to Pontificia
Universidad Catolica de Chile. During the past years the telescope has been refurbished and used as the main facility for
testing and validating new instruments under construction by the center of Astro-Engineering UC. As part of this work,
the need to develop a more efficient and flexible control system arises. The new distributed control system has been
developed on top of Internet Communication Engine (ICE), a framework developed by Zeroc Inc. This framework
features a lightweight but powerful and flexible inter-process communication infrastructure and provides binding to
classic and modern programming languages, such as, C/C++, java, c#, ruby-rail, objective c, etc. The result of this work
shows ICE as a real alternative for CORBA and other de-facto distribute programming framework. Classical control
software architecture has been chosen and comprises an observation control system (OCS), the orchestrator of the
observation, which controls the telescope control system (TCS), and detector control system (DCS). The real-time
control and monitoring system is deployed and running over ARM based single board computers. Other features such as
logging and configuration services have been developed as well. Inter-operation with other main astronomical control
frameworks are foreseen in order achieve a smooth integration of instruments when they will be integrated in the main
observatories in the north of Chile