Spectral multiplexing using stacked volume-phase holographic gratings - I

Many focal-reducer spectrographs, currently available at state-of-the-art telescopes facilities, would benefit from a simple refurbishing that could increase both the resolution and spectral range in order to cope with the progressively challenging scientific requirements, but, in order to make this update appealing, it should minimize the changes in the existing structure of the instrument. In the past, many authors proposed solutions based on stacking subsequently layers of dispersive elements and recording multiple spectra in one shot (multiplexing). Although this idea is promising, it brings several drawbacks and complexities that prevent the straightforward integration of such a device in a spectrograph. Fortunately, nowadays, the situation has changed dramatically, thanks to the successful experience achieved through photopolymeric holographic films, used to fabricate common volume-phase holographic gratings (VPHGs). Thanks to the various advantages made available by these materials in this context, we propose an innovative solution to design a stacked multiplexed VPHG that is able to secure efficiently different spectra in a single shot. This allows us to increase resolution and spectral range enabling astronomers to greatly economize their awarded time at the telescope. In this paper, we demonstrate the applicability of our solution, both in terms of expected performance and feasibility, supposing the upgrade of the Gran Telescopio CANARIAS (GTC) Optical System for Imaging and low-Intermediate-Resolution Integrated Spectroscopy (OSIRIS)

Photopolymeric films with highly tunable refractive index modulation for high precision diffractive optics

The design and manufacturing of high efficiency and reliable volume phase holographic optical elements require photosensitive material where it is possible to finely control the refractive index modulation. Bayfol HX photopolymers show this feature together with other interesting advantages, in particular the self-developing and the large refractive index modulation. In this paper, the design of Volume Phase Holographic Gratings (VPHGs) is reported underlying the relationship of gratings' performances with the refractive index modulation. The trend of this property with the change of the laser power density and the ratio of the two writing beams is shown. Based on these results, VPHGs for astronomical instrumentation have been designed and manufactured

Design of the VLT-CUBES image slicers: Field re-formatters to provide two spectral resolutions

CUBES is a high efficiency spectrograph designed for a Cassegrain focus of the Very Large Telescope and is expected to be in operation in 2028. It is designed to observe point or compact sources in a spectral range from 300 to 405nm. CUBES will provide two spectral resolving powers: R≥20,000 for high resolution (HR) and R≥5,000 for low resolution (LR). This is achieved by using an image slicer for each resolution mode. The image slicers re-format a rectangular on-sky field of view of either 1.5arcsec by 10arcsec (HR) or 6arcsec by 10arcsec (LR) into six side-by-side slitlets which form the spectrograph slit. The slit dimensions are 0.19mm × 88mm for HR and 0.77mm × 88mm for LR. The on-sky and physical widths of the slicer mirrors are 0.25arcsec/0.5mm (HR) and 1arcsec/2mm (LR). The image slicers reduce the spectrograph entrance slit etendue and hence the size of the spectrograph optics without associated slit losses. Each of the proposed image slicers consists of two arrays of six spherical mirrors (slicer mirror and camera mirror arrays) which provide a straight entrance slit to the spectrograph with almost diffraction-limited optical quality. This paper presents the description of the image slicers at the end of the Phase A conceptual design, including their optical design and expected performance

CUBES: application of image slicers to reformat the field for two spectral resolving powers

The Cassegrain U-Band Efficient Spectrograph (CUBES) is a high-efficiency spectrograph designed for observations from 305 to 400nm. It will be integrated at a Cassegrain focus of the Very Large Telescope (VLT). The image slicer technology is applied to reformat the field of view reducing the spectrograph entrance slit etendue and minimising the spectrograph volume and weight without slit losses. Two image slicers will provide CUBES with two spectral resolving powers: R≥20,000 for high resolution (HR) and R≥5,000 for low resolution (LR). Both image slicers are composed of two arrays of six spherical mirrors. For the HR mode, a rectangular field of view of 1.5arcsec by 10arcsec is reorganised into a slit of 0.19mm × 88mm; for the LR mode, a field of view of 6arcsec by 10arcsec is reformatted into a slit of 0.77mm × 88mm, with slicer mirrors of width 0.5mm and 2mm, respectively. CUBES is currently in the Preliminary Design Phase (Phase B). This communication presents the Conceptual (Phase A) design and the main performance for the HR and LR image slicers addressing the following technological challenges: compact layout with the minimum number of optical components to optimise throughput, near diffraction limited optical quality, telecentric design with overlapped exit pupils for all slices of the field of view, distribution of the slicer mirrors to reduce shadows and selection of the best substrate for the very short wavelengths at which CUBES will operate

Astro MBSE: overview on requirement management approaches for astronomical instrumentation

Systems Engineering requires the involvement of different engineering disciplines: Software, Electronics, Mechanics (often nowadays together as Mechatronics), Optics etc. Astronomical Instrumentation is no exception to this. A critical point is the handling of the requirements, their tracing, flow down and the interaction with stakeholders (flow up) and subsystems (flow down) in order to have traceable and methodical evolution and management. In the Italian Astronomical Community, we are developing methodologies and tools to share the expertise in this field among the different projects. In this paper we will focus on the requirement management approach among different projects (ground and space based, …). The target and synthesis of tis work will be a support framework for the Requirement management of the Italian Astronomical Community (INAF) projects

Compressive sampling for multispectral imaging in the vis-NIR-TIR: optical design of space telescopes

Micro-satellites equipped with multispectral payloads are now under development to acquire information on the radiation reflected and emitted from the earth in the vis-NIR-TIR bands. In this framework, we are studying different approaches based on the compressive sampling technique supported by innovative multispectral detectors, where the image sampling is performed on the telescope focal plane with a Digital Micromirror Device (DMD). We will describe in the paper the possibilities and the constraints given by the use of the DMD in the focal plane. The optical design of the telescope, relay system and detector in two different application cases will be provided

Astro MBSE: model based system engineering synthesized for the Italian astronomical community

Systems Engineering requires the involvement of different engineering disciplines: Software, Electronics, Mechanics (often nowadays together as Mechatronics), Optics etc. Systems Engineering of Astronomical Instrumentation is no exception to this. A critical point is the handling of the different point of view introduced by these disciplines often related to different tools and cultures. Model Based Systems Engineering (MBSE) approach can help the Systems Engineer to always have a complete view of the full system. Moreover, in an ideal situation, all of the information resides in the model thus allowing different views of the System without having to resort to different sources of information, often outdated. In the real world, however, this does not happen because the different actors (Optical Designers, Mechanical Engineers, Astronomers etc.) should adopt the same language and this is clearly, at least nowadays and for the immediate future, close to impossible. In the Italian Astronomical Community, we are developing methodologies and tools to share the expertise in this field among the different projects. In this paper we present the status of this activity that aims to deliver to the community proper tools and template to enable a uniformed use of MBSE (friendly name Astro MBSE) among different projects (ground and space based, …). We will analyze here different software and different approaches. The target and synthesis of this work will be a support framework for the MBSE based system Engineering activity to the Italian Astronomical Community (INAF)

UV-C irradiation is highly effective in inactivating SARS-CoV-2 replication

The potential virucidal effects of UV-C irradiation on SARS-CoV-2 were experimentally evaluated for different illumination doses and virus concentrations (1000, 5, 0.05 MOI). At a virus density comparable to that observed in SARS-CoV-2 infection, an UV-C dose of just 3.7 mJ/cm2 was sufficient to achieve a more than 3-log inactivation without any sign of viral replication. Moreover, a complete inactivation at all viral concentrations was observed with 16.9 mJ/cm2. These results could explain the epidemiological trends of COVID-19 and are important for the development of novel sterilizing methods to contain SARS-CoV-2 infection

INAF Raggruppamento Scientifico Nazionale 5 - Forum delle Tecnologie 2022

Il CSN5, rispondendo alle esigenze di creare maggiori occasioni di dialogo e di networking e di mettere a fattor comune le esperienze maturate in settori strategici del nostro Ente, ha organizzato il primo “Forum della Ricerca Sperimentale e Tecnologica INAF” che si è svolto presso l’area di ricerca di Bologna nei giorni 22, 23 e 24 giugno 2022. L'evento aveva diversi obiettivi: - incrementare la reciproca conoscenza delle attività tecnologiche condotte nelle diverse strutture INAF; - favorire discussioni, scambi, sinergie; - promuovere il senso di appartenenza alla comunità INAF; - introdurre e coinvolgere il personale assunto negli ultimi anni, che non dispone di una visione di insieme di tutte le attività svolte dall’INAF; - stimolare le collaborazioni, anche al di fuori dei rapporti già esistenti; - far emergere eventuali problematiche, discuterne insieme ed individuare possibili soluzioni; - in generale, migliorare la capacità dell’Ente nel realizzare strumentazione sempre più sofisticata e complessa