Bruno Femenia

Optimization with numerical simulations of the conjugate altitudes of deformable mirrors in an MCAO system

This article reports on the results of simulations conducte d to assess the performance of a modal Multi-Conjugate Adaptive Optics (MCAO) system on a 10m telescope with one Deformable Mirror (DM) conjugated to the telescope pupil and a second DM conjugated at a certain altitude above the pupil. The main goal of these simulations is to study the dependence of MCAO performance upon the altitude of the high-altitude conjugated DM and thereby determine its optimal conjugation. The performance is also studied with respect to the geometry of the Guide Star constellation when using constellations of Natural Guide Stars (NGS), which are rare, or constellations of Laser Guide Stars (LGS) which would allow large sky coverage.

Millimetric Ground-based Observations of Cosmic Microwave Background Anisotropy

First results of a cosmic microwave background (CMB) anisotropy experiment conducted at the Observatorio del Teide (Tenerife, Spain) are presented. The instrument is a four channel (3.1, 2.1, 1.3, and 1.1 mm)3He bolometer system coupled to a 45 cm diameter telescope. The resultant configuration is sensitive to structures on angular scales ~1°-2°. We use the channels at the two highest frequencies for monitoring the atmosphere and apply a simple method to subtract this contribution in channels 1 (3.1 mm) and 2 (2.1 mm). The most intense structure at these two frequencies is the Galactic crossing, with peak amplitudes of ~350 μK. These crossings have been clearly detected with the amplitude and shape predicted. This demonstrates that our multifrequency observations allow an effective assessment and subtraction of the atmospheric contribution. In the section of data at high Galactic latitude we obtain sensitivities ~40 μK beam-1. The statistical analyses show the presence of common signals between channels 1 and 2. Assuming a simple Gaussian autocorrelation model with a scale of coherence θc = 132 for the signal, a likelihood analysis of this section of data reveals the presence of fluctuations with intrinsic amplitude C01/2 = 76−32+42μK (with a 68% confidence limit including an ~20% calibration uncertainty). Since residual atmospheric noise might still contaminate our results, we also give our result as an upper limit of 118 μK at a 95% confidence limit.

Preliminary design and plans for the GTC adaptive optics system

The 10m Gran Telescopio Canarias (GTC) is currently being installed in the Observatorio del Roque de los Muchachos (ORM) on the island of La Palma. An adaptive optics (AO) system will be installed at one of the Nasmyth foci of the telescope within a year of the telescope being commissioned. The preliminary design of the adaptive optics system is presented here. The system will initially be operated in single-conjugate mode using a natural guide star, but provisions are made for upgrade to dual-conjugate operation and the use of laser guide stars. The main system requirements and the optical and mechanical design solutions are outlined here. It is planned to employ a piezo-stack deformable mirror having approximately 350 actuators and a Shack-Hartmann wavefront sensor. The tip-tilt correction will be provided by the secondary mirror of the GTC which is a lightweighted Beryllium mirror with a drive system capable of fast tip-tilt and chopping. In preparation for dual-conjugate operation we have studied the optimal altitude of the second deformable mirror (the first will be conjugate to the telescope pupil) using numerical simulations and measurements of turbulence obtained at the ORM. We have used the GSC II catalogue to determine sky-coverage for multi-natural guide star wavefront sensing, as required for dual-conjugate operation. In addition we have investigated a novel approach to multi-object wavefront sensing based on curvature sensing.

3D imaging and wavefront sensing with a plenoptic objective

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.

Millimetric Ground-Based Observation of Cosmic Microwave Background Radiation Anisotropy at δ = +28°

Results from the third campaign of a ground-based multiband observation of the millimeter emission of the sky from Tenerife (Canary Islands) are presented. The instrument consists of a 0.45 m diameter off-axis telescope equipped with a four-band multimode 3He cooled photometer working at 1.1, 1.3, 2.1, and 3.1 mm wavelengths. The beam is well approximated by a Gaussian with 135 FWHM at all wavelengths. The wide wavelength coverage of our instrument allows us to characterize and reduce both the atmospheric and Galactic contamination in our data. The cosmic microwave background radiation data is analyzed in six multipole bands whose centers span the range l = 39 to l = 134 at the two longest wavelengths (2.1 and 3.1 mm). A likelihood analysis indicates that we have detected fluctuations in all bands at the two wavelengths. We have evidence of a rise in the angular power spectrum from low l to high l. Our measured spectrum is consistent with current popular theories of large-scale structure formation, COBE, and other recent balloon-borne experiments with similar wavelength coverage.

The AOLI low-order non-linear curvature wavefront sensor: a method for high sensitivity wavefront reconstruction

The Adaptive Optics Lucky Imager (AOLI) is a new instrument under development to demonstrate near diffraction limited imaging in the visible on large ground-based telescopes. We present the adaptive optics system being designed for the instrument comprising a large stroke deformable mirror, fixed component non-linear curvature wavefront sensor and photon-counting EMCCD detectors. We describe the optical design of the wavefront sensor where two photoncounting CCDs provide a total of four reference images. Simulations of the optical characteristics of the system are discussed, with their relevance to low and high order AO systems. The development and optimisation of high-speed wavefront reconstruction algorithms are presented. Finally we discuss the results of simulations to demonstrate the sensitivity of the system.

Adaptive optics simulations for imaging with the Large Binocular Telescope interferometer: a first application

In this contribution we present a first application of the ongoing numerical simulations that are carried out in order to study the adaptive optics (AO) correction and the subsequent imaging post-processing when observing with the Large Binocular Telescope (LBT) interferometer. The simulation tool used as a starting point for this study is the software package CAOS 2.0 (Code for Adaptive Optics Systems, version 2.0), for its AO-simulation capabilities and its modular structure. It is used here in order to generate the turbulence-corrupted and subsequently adaptive-optics- corrected interferometric point-spread functions corresponding to the simultaneous observation of both a scientific object and a reference star, for three parallactic angles corresponding to three observation runs during the night. The obtained data are therefore used as the inputs of a multiple deconvolution method planned for imaging with the LBT interferometer. As an example, we have simulated the observation, in the R-band, of a Betelgeuse-like stellar object of 15th magnitude, 30 mas diameter, and with a 3 mas bright spot, under two different conditions of turbulence and AO-correction (leading to Strehl ratios of approximately 0.15 and approximately 0.45, respectively). Final results are found to be very encouraging.

Laboratory and telescope demonstration of the TP3-WFS for the adaptive optics segment of AOLI

This work was supported by the Spanish Ministry of Economy under the projects AYA2011-29024, ESP2014-56869-C2-2-P, ESP2015-69020-C2-2-R and DPI2015-66458-C2-2-R, by project 15345/PI/10 from the Fundacion Seneca, by the Spanish Ministry of Education under the grant FPU12/05573, by project ST/K002368/1 from the Science and Technology Facilities Council and by ERDF funds from the European Commission. The results presented in this paper are based on observations made with the William Herschel Telescope operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. Special thanks go to Lara Monteagudo and Marcos Pellejero for their timely contributions.

Atmospherical wavefront phases using the plenoptic sensor (real data)

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 telescope. 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 turbulence.

High spatial resolution and high contrast optical speckle imaging with FASTCAM at the ORM

In this paper, we present an original observational approach, which combines, for the first time, traditional speckle imaging with image post-processing to obtain in the optical domain diffraction-limited images with high contrast (10-5) within 0.5 to 2 arcseconds around a bright star. The post-processing step is based on wavelet filtering an has analogy with edge enhancement and high-pass filtering. Our I-band on-sky results with the 2.5-m Nordic Telescope (NOT) and the lucky imaging instrument FASTCAM show that we are able to detect L-type brown dwarf companions around a solar-type star with a contrast ▵I~12 at 2 and with no use of any coronographic capability, which greatly simplifies the instrumental and hardware approach. This object has been detected from the ground in J and H bands so far only with AO-assisted 8-10 m class telescopes (Gemini, Keck), although more recently detected with small-class telescopes in the K band. Discussing the advantage and disadvantage of the optical regime for the detection of faint intrinsic fluxes close to bright stars, we develop some perspectives for other fields, including the study of dense cores in globular clusters. To the best of our knowledge this is the first time that high contrast considerations are included in optical speckle imaging approach.