Roberto Ragazzoni

Layer-oriented simulation tool

The Layer-Oriented Simulation Tool (LOST) is a numerical simulation code developed for analysis of the performance of multiconjugate adaptive optics modules following a layer-oriented approach. The LOST code computes the atmospheric layers in terms of phase screens and then propagates the phase delays introduced in the natural guide stars wave fronts by using geometrical optics approximations. These wave fronts are combined in an optical or numerical way, including the effects of wave-front sensors on measurements in terms of phase noise. The LOST code is described, and two applications to layer-oriented modules are briefly presented. We have focus on the Multiconjugate adaptive optics demonstrator to be mounted upon the Very Large Telescope and on the Near-IR-Visible Adaptive Interferometer for Astronomy (NIRVANA) interferometric system to be installed on the combined focus of the Large Binocular Telescope.

Optical design of the Wide Angle Camera for the Rosetta mission

The final optical design of the Wide Angle Camera for the Rosetta mission to the P/Wirtanen comet is described. This camera is an F/5.6 telescope with a rather large 12 degrees x 12 degrees field of view. To satisfy the scientific requirements for spatial resolution, contrast capability, and spectral coverage, a two-mirror, off-axis, and unobstructed optical design, believed to be novel, has been adopted. This configuration has been simulated with a ray-tracing code, showing that theoretically more than 80% of the collimated beam energy falls within a single pixel (20 x 20) over the whole camera field of view and that the possible contrast ratio is smaller than 1/1000. Moreover, this novel optical design is rather simple from a mechanical point of view and is compact and relatively easy to align. All these characteristics make this type of camera rather flexible and also suitable for other space missions with similar performance requirements.

Commissioning multi-conjugate adaptive optics with LINC-NIRVANA on LBT

This paper reports on early commissioning of LINC-NIRVANA (LN), an innovative Multi-Conjugate Adaptive Optics (MCAO) system for the Large Binocular Telescope (LBT). LN uses two, parallel MCAO systems, each of which corrects turbulence at two atmospheric layers, to deliver near diffraction-limited imagery over a two-arcminute field of view. We summarize LN’s approach to MCAO and give an update on commissioning, including the achievement of First Light in April 2018. This is followed by a discussion of challenges that arise from our particular type of MCAO and the solutions implemented. We conclude with a brief look forward to the remainder of commissioning and future upgrades.

Pyramid wavefront sensor aboard AdOpt@TNG and beyond: a status report

The concept of Pyramid Wavefront sensor has been introduced as a more compact and flexible alternative to Shack--Hartmann wavefront sensing. In the past five years, however, such a novel concept promised a much larger sensitivity and an inherent easiness to be implemented in a multiple reference wavefront sensor. AdOptTNG, a natural guide star based adaptive optics module implemented at the 3.5m TNG telescope is equipped with such a sensor. We report here on the updated status, including on-sky experimental verification of various of the several features of such a sensor. We discuss the results obtained, their scalability and the lessons learned in building, aligning and operating it. Some comparison with theoretical and laboratory-based result, is also tentatively reported.

Installation and commissioning of the LINC-NIRVANA near-infrared MCAO imager on LBT

This paper reports on the installation and initial commissioning of LINC-NIRVANA (LN), an innovative high resolution, near-infrared imager for the Large Binocular Telescope (LBT). We present the delicate and difficult installation procedure, the culmination of a re-integration campaign that was in full swing at the last SPIE meeting. We also provide an update on the ongoing commissioning campaigns, including our recent achievement of First Light. Finally, we discuss lessons learned from the shipment and installation of a large complex instrument.

Numerical simulations of MAORY MCAO module for the ELT

MAO (MAORY Adaptive Optics) is the a developed numerical simulation tool for adaptive optics. It was created especially to simulate the performance of the MAORY MCAO module of the Extremely Large Telescope. It is a full end-to-end Monte-Carlo code able to perform different flavors of adaptive optics simulation. We used it to investigate the performance of a the MAORY and some specific issue related to calibration, acquisition and operation strategies. As, MAORY, MAO will implement Multi-conjugate Adaptive Optics combining Laser Guide Stars (LGS) and Natural Guide Stars (NGS) measurements. The implementation of the reference truth WFS completes the scheme. The simulation tool implements the various aspect of the MAORY in an end to end fashion. The code has been developed using IDL and use libraries in C++ and CUDA for efficiency improvements. Here we recall the code architecture, we describe the modeled instrument components and the control strategies implemented in the code.

Optical alignment of the Galileo telescope: results and on-sky test before active optics final tuning

Optical alignment is a crucial step in the commitment of a telescope. The accuracy in which it is accomplished has a deep impact in the future life of the telescope. The Galileo Telescope, sited in La Palma, is a 3.58 meters telescope with active optics and has recently undergone its final optical alignment. The result of the alignment, obtained in the so-called passive mode, that is just before switching- on the active optics system, are here presented. The alignment consisted in the definitions of the mechanical axes of the structure and mirrors supports and of the optical axis of the entire telescope, using three high precision alignment telescopes and their relative targets. The final step has been to take some images on the sky looking at point like objects and to measure the point spread function in terms of full width at half maximum. The first star imaged in our passive alignment test on the sky had a FWHM of 0.8 arcsec, well inside the range of the active optics system correction, making it totally usable for the following fine-tuning of the optics.

Versatile wavefront simulator

A new concept for a device able to simulate evolving atmospherically distorted wavefronts for the adaptive optics system of the Italian facility Telescopio Nazionale Galileo (TNG) is presented. The goodness of performances of an adaptive optics system depends upon the testing accuracy of its components made under different seeing conditions. Moreover, in order to not loose good seeing nights, the possibility to perform tests during day-light can become strongly important. Introducing a simulator able to generate the image of an astronomical object deformed by atmosphere can help to solve many such problems. In order to create the wanted distortion we use phase changing plate (PCP) screens. A system of moving screens and adjustable zooms provides to change, over a wide range, some fundamental parameters of the atmosphere turbulence like fired parameter ro, Greenwood frequency fG and the isoplanatic angle (theta) o.

Preliminary optical design for Plures and Rosetta

Some preliminary optical designs for three wide field cameras are briefly reported for the space missions Plures and Rosetta. Plures is a proposal to the European Space Agency (ESA) for a wide field telescope able to detect Supernova explosions with a time resolution of the order of a fraction of a minute. After the Supernova detection the telescope should switch to a narrow, single-object mode in order to probe the event in a photometric and spectroscopic mode. Plures should continuously monitor the Virgo cluster with a field of view of the order of 100 squared degrees. Rosetta is a cornerstone mission of ESA for the approaching of a cometary body, after the fly-by with two asteroids. In the approach phase Rosetta should orbit around the comet. Two cameras will map and probe the surface of the comet nucleus. For the three optics all-reflective unobstructed solutions are presented.

A comparison between the opto-thermo-mechanical model and lab measurements for CHEOPS

CHEOPS is the first small class mission adopted by ESA in the framework of the Cosmic Vision 2015-2025. Its launch is foreseen in early 2019. CHEOPS aims to get transits follow-up measurements of already known exo-planets, hosted by near bright stars (V<12). Thanks to its ultra-high precision photometry, CHEOPS science goal is accurately measure the radii of planets in the super-Earth to Neptune mass range (1<Mplanet/MEarth<20). The knowledge of the radius by transit measurements, combined with the determination of planet mass through radial velocity techniques, will allow the determination/refinement of the bulk density for a large number of small planets during the scheduled 3.5 years life mission. The instrument is mainly composed of a 320 mm aperture diameter Ritchey-Chretien telescope and a Back End Optics, delivering a de-focused star image onto the focal plane. In this paper we describe the opto-thermo-mechanical model of the instrument and the measurements obtained during the opto-mechanical integration and alignment phase at Leonardo company premises, highlighting the level of congruence between the predictions and measurements.