The GTC AO system designed and developed during the last years is based on a single deformable mirror with 21 x 21 actuators, conjugated to the telescope pupil, and a Shack-Hartmann wavefront sensor with 20 x 20 subapertures, using an OCAM2 camera. The GTCAO system will provide a corrected beam with a Strehl Ratio (SR) of 0.65 in K-band with bright natural guide stars. This paper reports the updated status of the integration of GTCAO in the IAC laboratory, and the results obtained in the first tests carried out to evaluate the performance of the system, before the complete characterization and the verification of the requirements. The wavefront sensor verification has been completed, and it has been integrated in the optical bench together with the corrector optics including the CILAS deformable mirror. The calibration system, also mounted on the optical bench, includes light sources used to tune, characterise and calibrate the whole system. It also simulates the atmospheric turbulence and the telescope, delivering an aberrated wavefront used to debug the whole control system, and to test the real time control software, the servo loop and different servo control strategies. Finally the Test Camera has been also integrated at the science focus to evaluate the performance.
The Gran Telescopio Canarias Adaptive Optics (GTCAO) will measure the wavefront with a Shack-Hartmann sensor. This wavefront sensor (WFS) is based on the CCD220, an electron-multiplying CCD (EMCCD) that achieves sub-electron readout noise, increasing the signal to noise ratio when weak natural guide stars (NGS) are used as reference. GTCAO will start its operation in telescope with NGS, using only one wavefront sensor, and later it will incorporate a Laser Guide Star (LGS) and consequently a second WFS, also based on an EMCCD. Both EMCCDs and a third one used as spare, have been characterized and compared including the system gain, electron- multiplication gain, readout noise vs gain, excess noise and linearity. The EM gain calibration is important to keep all EMCCD channels in the linear regime and the camera manufacturer carries it out, but it is reported that the multiplication gain may suffer ageing and degradation even if the camera is not in use. This suggests the need to monitor this ageing. In this paper it is proposed and tested a procedure for predictive maintenance that re-characterize the system gain, electron- multiplication gain and linearity periodically in order to predict the eventual ageing of the EMCCD multiplying registers. This procedure can be carried out quickly while the detector is installed in the WFS and in operational status. In order to provide the required illumination, the GTCAO calibration system is used.
The Gran Telescopio Canarias Adaptive Optics (GTCAO) is a single-conjugated post-focal system with a Shack Hartmann wavefront sensor working at visible wavelength and one Deformable Mirror (DM) conjugated to the pupil. GTCAO does not include a fast tip-tilt mirror in its optical bench so it relies on the telescope secondary mirror (M2) to correct low frequency tip-tilt and offload the DM. This paper describes specific details of the software implementation of the mirror control for GTCAO, analyses its computational needs, presents the series of tests performed on the newly designed AO closed loop, and summarises software optimizations and operating system configurations set in order to optimise computer performance in the available hardware architecture
The Gran Telescopio Canarias Adaptive Optics (GTCAO) is a single-conjugated post-focal system with a Shack Hartmann wavefront sensor, and one Deformable Mirror (DM) conjugated to the pupil. The optical design for tip-tilt correction includes two different mirrors, DM and the telescope M2, being M2 also used for off-loading the DM to avoid reaching its stroke limits. This optical configuration is open to different control strategies that have been simulated with Matlab. Later it has also been simulated using Durham Adaptive optics Real-time Controller (DARC) and its AO simulator, DASP. Finally some preliminary laboratory results are presented.
The combination of Lucky Imaging with a low order adaptive optics system was demonstrated very successfully on the Palomar 5m telescope nearly 10 years ago. It is still the only system to give such high-resolution images in the visible or near infrared on ground-based telescope of faint astronomical targets. The development of AOLI for deployment initially on the WHT 4.2 m telescope in La Palma, Canary Islands, will be described in this paper. In particular, we will look at the design and status of our low order curvature wavefront sensor which has been somewhat simplified to make it more efficient, ensuring coverage over much of the sky with natural guide stars as reference object. AOLI uses optically butted electron multiplying CCDs to give an imaging array of 2000 x 2000 pixels.
The Adaptive Optics Lucky Imager, AOLI, is an instrument developed to deliver the highest spatial resolution ever obtained in the visible, 20 mas, from ground-based telescopes. In AOLI a new philosophy of instrumental prototyping has been applied, based on the modularization of the subsystems. This modular concept offers maximum flexibility regarding the instrument, telescope or the addition of future developments.
The FastCam instrument platform, jointly developed by the IAC and the UPCT, allows, in real-time, acquisition, selection and storage of images with a resolution that reaches the diffraction limit of medium-sized telescopes. FastCam incorporates a specially designed software package to analyse series of tens of thousands of images in parallel with the data acquisition at the telescope. Wide FastCam is a new instrument that, using the same software for data acquisition, does not look for lucky imaging but fast observations in a much larger field of view. Here we describe the commissioning process and first observations with Wide FastCam at the Telescopio Carlos Sanchez (TCS) in the Observatorio del Teide.
Since the beginning of the development of the Gran Telescopio Canarias (GTC), an Adaptive Optics (AO) system was considered necessary to exploit the full diffraction-limited potential of the telescope. The GTC AO system designed during the last years is based on a single deformable mirror conjugated to the telescope pupil, and a Shack-Hartmann wavefront sensor with 20 x 20 subapertures, using an OCAM2 camera. The GTCAO system will provide a corrected beam with a Strehl Ratio (SR) of 0.65 in K-band with bright natural guide stars. <p> </p>Most of the subsystems have been manufactured and delivered. The upgrade for the operation with a Laser Guide Star (LGS) system has been recently approved. The present status of the GTCAO system, currently in its laboratory integration phase, is summarized in this paper.
This paper reviews the EDiFiSE (Equalized and Diffraction-limited Field Spectrograph Experiment) full-FPGA (Field Programmable Gate Array) adaptive optics (AO) system and presents its first laboratory results. EDiFiSE is a prototype equalized integral field unit (EIFU) spectrograph for the observation of high-contrast systems in the Willian Herschel Telescope (WHT). Its AO system comprises two independent parallel full-FPGA control loops, one for tip-tilt and one for higher order aberrations. Xilinx's Virtex-4 and Virtex-5 FPGA's fixed point arithmetic and their interfacing with the rest of the AO components and the user have been adequately dealt with, and a very deterministic system with a negligible computational delay has been obtained. The AO system has been recently integrated in laboratory and verified using the IACAT (IAC Atmosphere and Telescope) optical ground support equipment. Closed loop correction bandwidths of 65 Hz for the tip-tilt and 25 Hz for higher order aberrations are obtained. The system has been tested in the visible range for the WHT with a 9 x 9 subpupil configuration, low star magnitude, wind speeds up to 10 m/s and Fried parameter down to 18 cm, and a resolution below the EIFU’s fiber section has been obtained.
Lucky Imaging combined with a low order adaptive optics system has given the highest resolution images ever taken in
the visible or near infrared of faint astronomical objects. This paper describes a new instrument that has already been
deployed on the WHT 4.2m telescope on La Palma, with particular emphasis on the optical design and the predicted
system performance. A new design of low order wavefront sensor using photon counting CCD detectors and multi-plane
curvature wavefront sensor will allow virtually full sky coverage with faint natural guide stars. With a 2 x 2 array of
1024 x 1024 photon counting EMCCDs, AOLI is the first of the new class of high sensitivity, near diffraction limited
imaging systems giving higher resolution in the visible from the ground than hitherto been possible from space.
AOLI, Adaptive Optics Lucky Imager, is the next generation of extremely high resolution instruments in the optical
range, combining the two more promising techniques: Adaptive optics and lucky imaging. The possibility of reaching
fainter objects at maximum resolution implies a better use of weak energy on each lucky image. AOLI aims to achieve
this by using an adaptive optics system to reduce the dispersion that seeing causes on the spot and therefore increasing
the number of optimal images to accumulate, maximizing the efficiency of the lucky imaging technique.
The complexity of developments in hardware, control and software for in-site telescope tests claim for a system to
simulate the telescope performance. This paper outlines the requirements and a concept/preliminary design for the
William Herschel Telescope (WHT) and atmospheric turbulence simulator. The design consists of pupil resemble, a
variable intensity point source, phase plates and a focal plane mask to assist in the alignment, diagnostics and calibration
of AOLI wavefront sensor, AO loop and science detectors, as well as enabling stand-alone test operation of AOLI.
The plenoptic camera was originally created to allow the capture of the Light Field, a four-variable volume
representation of all rays and their directions, that allows the creation by synthesis of a 3D image of the observed
object. This method has several advantages with regard to 3D capture systems based on stereo cameras, since
it does note need frame synchronization or geometric and color calibration. And it has many applications, from
3DTV to medical imaging. A plenoptic camera uses a microlens array to measure the radiance and direction of
all the light rays in a scene. The array is placed at the focal plane of the objective lens, and the sensor is at
the focal plane of the microlenses. In this paper we study the application of our super resolution algorithm to
mobile phones cameras. With a commercial camera, it is already possible to obtain images of good resolution
and enough number of refocused planes, just placing a microlens array in front of the detector.
Plenoptic cameras have been developed the last years as a passive method for 3d scanning, allowing focal stack capture
from a single shot. But data recorded by this kind of sensors can also be used to extract the wavefront phases associated
to the atmospheric turbulence in an astronomical observation.
The terrestrial atmosphere degrades the telescope images due to the diffraction index changes associated to the
turbulence. Na artificial Laser Guide Stars (Na-LGS, 90km high) must be used to obtain the reference wavefront phase
and the Optical Transfer Function of the system, but they are affected by defocus because of the finite distance to the
Using the telescope as a plenoptic camera allows us to correct the defocus and to recover the wavefront phase
tomographically, taking advantage of the two principal characteristics of the plenoptic sensors at the same time: 3D
scanning and wavefront sensing. Then, the plenoptic sensors can be studied and used as an alternative wavefront sensor
for Adaptive Optics, particularly relevant when Extremely Large Telescopes projects are being undertaken.
In this paper, we will present the first observational wavefront phases extracted from real astronomical observations,
using punctual and extended objects, and we show that the restored wavefronts match the Kolmogorov atmospheric
Plenoptic cameras have been developed over the last years as a passive method for 3d scanning. Several superresolution
algorithms have been proposed in order to increase the resolution decrease associated with lightfield acquisition with a
microlenses array. A number of multiview stereo algorithms have also been applied in order to extract depth information
from plenoptic frames. Real time systems have been implemented using specialized hardware as Graphical Processing
Units (GPUs) and Field Programmable Gates Arrays (FPGAs).
In this paper, we will present our own implementations related with the aforementioned aspects but also two new
developments consisting of a portable plenoptic objective to transform every conventional 2d camera in a 3D CAFADIS
plenoptic camera, and the novel use of a plenoptic camera as a wavefront phase sensor for adaptive optics (OA).
The terrestrial atmosphere degrades the telescope images due to the diffraction index changes associated with the
turbulence. These changes require a high speed processing that justify the use of GPUs and FPGAs. Na artificial Laser
Guide Stars (Na-LGS, 90km high) must be used to obtain the reference wavefront phase and the Optical Transfer
Function of the system, but they are affected by defocus because of the finite distance to the telescope. Using the
telescope as a plenoptic camera allows us to correct the defocus and to recover the wavefront phase tomographically.
These advances significantly increase the versatility of the plenoptic camera, and provides a new contribution to relate
the wave optics and computer vision fields, as many authors claim.