Spectrograph sensitivity analysis: an efficient tool for different design phases

In this paper we present an efficient tool developed to perform opto-mechanical tolerance and sensitivity analysis both for the preliminary and final design phases of a spectrograph. With this tool it will be possible to evaluate the effect of mechanical perturbation of each single spectrograph optical element in terms of image stability, i.e. the motion of the echellogram on the spectrograph focal plane, and of image quality, i.e. the spot size of the different echellogram wavelengths. We present the MATLAB-Zemax script architecture of the tool. In addition we present the detailed results concerning its application to the sensitivity analysis of the ESPRESSO spectrograph (the Echelle Spectrograph for Rocky Exoplanets and Stable Spectroscopic Observations which will be soon installed on ESO's Very Large Telescope) in the framework of the incoming assembly, alignment and integration phases

Optical parametric evaluation model for a broadband high resolution spectrograph at E-ELT (E-ELT HIRES)

We present the details of a paraxial parametric model of a high resolution spectrograph which can be used as a tool, characterized by good approximation and reliability, at a system engineering level. This model can be exploited to perform a preliminary evaluation of the different parameters as long as different possible architectures of high resolution spectrograph like the one under design for the E-ELT (for the moment called E-ELT HIRES in order to avoid wrong association with the HIRES spectrograph at Keck telescope). The detailed equations flow concerning the first order effects of all the spectrograph components is described; in addition a comparison with the data of a complete physical ESPRESSO spectrograph model is presented as a model proof

Integration and alignment through mechanical measurements: the example of the ESPRESSO front-end units

Traditional techniques usually rely on optical feedback to align optical elements over all the degrees of freedom needed. This strongly iterative process implies the use of bulky and/or flexible adjustable mountings. Another solution under study consists in the characterization of every optomechanical elements and the integration of the parts without any optical feedback. The characterization can be performed using different 3D Coordinate Measuring Machines (like Laser Tracker, Articulated Arms and Cartesian ones) and referencing different parts like the optomechanical mounts or the optical surfaces. The alignment of the system is done adjusting the six degrees of freedom of every element with metallic shims. Those calibrated elements are used to correct the interfaces position of the semikinematic system composed by 3 screws and 3 pins. In this paper, the integration and alignment of the ESPRESSO Front End Units (FEUs) will be used as pathfinder to test different alignment methods and evaluate their performances

Alignment and integration of large optical systems based on advanced metrology

Optical alignment is a key activity in opto-mechanical system Integration. Traditional techniques require adjustable mounting, driven by optical references that allows the tuning of the optics position along all 6 Degree of Freedom. Nevertheless, the required flexibility imposes reduced stiffness and consequently less stability of the system. The Observatory of Brera (OAB) started few years ago a research activity focused onto the overcoming of this limits exploiting the high metrology performances of Coordinate Measuring Machines (CMM) with the main objectives of relax the manufacturing tolerances and maximize mounting stiffness. Through the T-REX grants, OAB acquired all the instrumentation needed for that activity furthermore considering the ESPRESSO project training and testing also oriented to large scale instrumentation like the E-ELT one. We will present in this paper the definition of the VLTs convergence point and the feasibility study of large mirrors alignment done by mechanical measurements methods

MMP, the Multi Mini Prism device for ESPRESSO APSU: prototyping and integration

The multi mini prism device is a crucial component of the Espresso Anamorphic Pupil Slicer (APSU). At the end of the slicer, is necessary to differently fold each field to correctly illuminate the echelle and this is made by cylindrical prisms glued onto a silica window. We present the integrated robotic system conceived to reach the required tolerances in term of alignment and integration. It consists in a tip/tilt stage to select the wedge angle, a rotational stage to select the right clock angle, coupled to an x-y stage to position the elements on the window and a z axis to perform the gluing

An adaptive interferometer for optical testing

Interferometry is a well-established technique to test optical elements. However, its use is challenging in the case of free-form and aspheric elements, due to the lack of the reference optics. The proposed idea concerns the development of a versatile interferometer, where its reference arm is equipped with a reprogrammable Computer Generated Hologram. This principle takes advantage from our study on photochromic materials for optical applications, which shows a strong and reversible modulation of transparency in the visible region. The encoding of the desired hologram can be done off-line, or directly into the interferometer, and different patterns may be realized sequentially after the erasing of the previous hologram. We report on the present state of the research and on the future perspectives. skip=5p

MITS: the Multi-Imaging Transient Spectrograph for SOXS

The Son Of X-Shooter (SOXS) is a medium resolution spectrograph R~4500 proposed for the ESO 3.6 m NTT. We present the optical design of the UV-VIS arm of SOXS which employs high efficiency ion-etched gratings used in first order (m=1) as the main dispersers. The spectral band is split into four channels which are directed to individual gratings, and imaged simultaneously by a single three-element catadioptric camera. The expected throughput of our design is >60% including contingency. The SOXS collaboration expects first light in early 2021. This paper is one of several papers presented in these proceedings describing the full SOXS instrument

Optical design of the SOXS spectrograph for ESO NTT

An overview of the optical design for the SOXS spectrograph is presented. SOXS (Son Of X-Shooter) is the new wideband, medium resolution (R>4500) spectrograph for the ESO 3.58m NTT telescope expected to start observations in 2021 at La Silla. The spectroscopic capabilities of SOXS are assured by two different arms. The UV-VIS (350-850 nm) arm is based on a novel concept that adopts the use of 4 ion-etched high efficiency transmission gratings. The NIR (800- 2000 nm) arm adopts the '4C' design (Collimator Correction of Camera Chromatism) successfully applied in X-Shooter. Other optical sub-systems are the imaging Acquisition Camera, the Calibration Unit and a pre-slit Common Path. We describe the optical design of the five sub-systems and report their performance in terms of spectral format, throughput and optical quality. This work is part of a series of contributions describing the SOXS design and properties as it is about to face the Final Design Review.Comment: 9 pages, 9 figures, published in SPIE Proceedings 1070

The VIS detector system of SOXS

SOXS will be a unique spectroscopic facility for the ESO NTT telescope able to cover the optical and NIR bands thanks to two different arms: the UV-VIS (350-850 nm), and the NIR (800-1800 nm). In this article, we describe the design of the visible camera cryostat and the architecture of the acquisition system. The UV-VIS detector system is based on a e2v CCD 44-82, a custom detector head coupled with the ESO continuous ow cryostats (CFC) cooling system and the NGC CCD controller developed by ESO. This paper outlines the status of the system and describes the design of the different parts that made up the UV-VIS arm and is accompanied by a series of contributions describing the SOXS design solutions.Comment: 9 pages, 13 figures, to be published in SPIE Proceedings 1070

The Acquisition Camera System for SOXS at NTT

SOXS (Son of X-Shooter) will be the new medium resolution (R$\sim$4500 for a 1 arcsec slit), high-efficiency, wide band spectrograph for the ESO-NTT telescope on La Silla. It will be able to cover simultaneously optical and NIR bands (350-2000nm) using two different arms and a pre-slit Common Path feeding system. SOXS will provide an unique facility to follow up any kind of transient event with the best possible response time in addition to high efficiency and availability. Furthermore, a Calibration Unit and an Acquisition Camera System with all the necessary relay optics will be connected to the Common Path sub-system. The Acquisition Camera, working in optical regime, will be primarily focused on target acquisition and secondary guiding, but will also provide an imaging mode for scientific photometry. In this work we give an overview of the Acquisition Camera System for SOXS with all the different functionalities. The optical and mechanical design of the system are also presented together with the preliminary performances in terms of optical quality, throughput, magnitude limits and photometric properties.Comment: 9 pages, 7 figures, SPIE conferenc