Conceptual Design of an On-Axis 6 m Space Telescope at the Diffraction Limit: Characteristics, Performance and Advantages

This paper presents the conceptual design of an on-axis 6 metre aperture space telescope designed to cover a field of view of ±0.2 degrees with an optical quality at the diffraction limit within a spectral range between 0.5 μm and 2.5 μm. The plate scale is 3 arcsec/mm, and the overall length is less than 12 m. A Korsch layout has been selected based on the superb aberration compensation offered by Three-Mirror Anastigmat systems. The proposed design presents some characteristics: an almost flat response in RMS wavefront error across the field and for the entire spectral range; a flat mirror has been included to reduce the overall volume, and this has been adjusted to be placed at an intermediate pupil position, acting as a baffle for stray light and as a Lyott to restrict background radiation. This mirror presents a central hole, defined to the aperture of the pupil, allowing the transmission of the beam towards the image focal plane, where it can be split for multiple payloads. It also allows the transmission of the central field, at 90 degrees with respect to the science beam, to be used for Active Optics monitoring and correction of the primary mirror in order to ensure optimum optical performance. This on-axis solution significantly reduces the technical complexity for manufacturing, metrology, integration, and tests and has an important impact in the cost of the telescope

Exploring the application of image slicers for the EUV for the next generation of solar space missions

The Sun is a privileged place to study particle acceleration, a fundamental astrophysical problem throughout the universe. The extreme ultra-violet (EUV) contains a number of narrow emission lines formed in all layers of the solar atmosphere whose profiles allow the measurement of plasma properties like density and temperature, along with the presence of non-Maxwellian particle distributions to be diagnosed. The only way to observe is from space, since EUV radiation is absorbed by the Earth’s atmosphere. Integral field spectroscopy combined with polarimetry is key for the study of the Sun, but the current EUV technology is limiting: the transmission of optical fibers IFUs (integral field units) is low and in-flight effects affect polarisation measurements. The best solution seems to be image slicers. However, this technology has not yet been developed for the EUV spectral range. This communication explores a new highly efficient and compact integral field spectrograph layout based on the application of image slicers combining the surfaces of the IFU with those of the spectrograph, suitable for space applications

Optical Design of a Miniaturised Solar Magnetograph for Space Applications

Measuring the Sun’s magnetic field is a key component of monitoring solar activity and forecasting space weather. The main goal of the research presented in this paper is to investigate the possibility of reducing the dimensions and weight of a solar magnetograph while preserving its optical quality. This article presents a range of different designs, along with their advantages and disadvantages, and an analysis of the optical performance of each. All proposed designs are based on the magneto-optical filter (MOF) technique. As a result of the design study, a miniaturised solar magnetograph is proposed with an ultra-compact layout. The dimensions are 345 mm × 54 mm × 54 mm, and the optical quality is almost at the diffraction limit. The design has an entrance focal ratio of F/17.65, with a plate scale of 83.58 arcsec/mm at the telescope image focal plane, and produces a magnification of 0.79. The field of view is 1920 arcsec in diameter, equivalent to ±0.27 degrees, sufficient to cover the entire solar disk

The HR image slicer for GNIRS at Gemini North: optical design and performance

GNIRS (Gemini Near-InfraRed Spectrograph) is a multi-function spectrograph at Gemini North telescope offering four observational modes in the spectral range of 0.8 to 5.4 µm. It provides 2-pixel spectral resolutions from 1,200 up to 18,0000 and has single disperser and cross-disperser modes yielding simultaneous spectral bandwidths from 40 nm to 1,650 nm. GNIRS presented three existing modes: long-slit (50-100" slit), cross-dispersed (5-7" slit) and low resolution (LR) Integral Field Unit (IFU) (3.15" x 4.80") and it is now being upgraded with a fourth mode allowing high resolution (HR) IFU spectroscopy using an image slicer optimised for fully adaptively corrected images over a field of view of 2.25 arcsec2 (1.80" x 1.25") covered by 25 slices of 410 µm width offering a spatial sampling of 0.05 x 0.05 arscec2 with a diffraction limited optical quality. The proposed layout meets specifications and some challenging design constraints: it shall be contained within the same envelope defined by the LR image slicer (0.1 x 0.2 x 0.1 m3 ), the input and output focal-ratios of both image slicers shall be the same and at exact positions but providing different anamorphic magnifications and preserving the optical quality. The length of the generated slit will be similar to the length of the slit in long-slit mode to maximise detector use and avoid vignetting. This communication presents the optical design and performance of the high resolution image slicer compliant with all specifications and constraints and it shows some design adaptations adopted in order to facilitate its manufacturing in metal at Durham University

WIVERN: a laboratory experiment for testing novel laser-based wavefront sensing techniques

WIVERN is a testbed for laboratory experiments in laser-based wavefront sensing. It emulates laser uplink from a 4m telescope with 1.6 arcsec seeing and laser back-scattering from up to 20 km. Currently there are three current wavefront sensing capabilities. The first two are from a wide-field of view (1.0 arcmin) Shack Hartmann wavefront sensor observing a constellation of point sources at infinity (reference targets, star-oriented wavefront sensing), or an image from emulated back-scattering (wide-field correlation wavefront sensing). The third is based on the PPPP concept. Other sub-systems are laser projection replicating a pupil launch, a 7x7 pupil-conjugate deformable mirror (DM), and a wide-field camera for PSF analysis. A 500 Hz rate accumulates sufficient data for statistical and machine-learning analysis over hour timescales. It is a compact design (2.1m2) with mostly commercial dioptric components. The sub-system optical interfaces are identical: a flat focal plane for easy bench reconfiguration. The end-to-end design is diffraction-limited with ≤ 1% pupil distortion for wavelengths λ=633–750 nm

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

Spectral Imager of the Solar Atmosphere: The First Extreme-Ultraviolet Solar Integral Field Spectrograph Using Slicers

Particle acceleration, and the thermalisation of energetic particles, are fundamental processes across the universe. Whilst the Sun is an excellent object to study this phenomenon, since it is the most energetic particle accelerator in the Solar System, this phenomenon arises in many other astrophysical objects, such as active galactic nuclei, black holes, neutron stars, gamma ray bursts, solar and stellar coronae, accretion disks and planetary magnetospheres. Observations in the Extreme Ultraviolet (EUV) are essential for these studies but can only be made from space. Current spectrographs operating in the EUV use an entrance slit and cover the required field of view using a scanning mechanism. This results in a relatively slow image cadence in the order of minutes to capture inherently rapid and transient processes, and/or in the spectrograph slit ‘missing the action’. The application of image slicers for EUV integral field spectrographs is therefore revolutionary. The development of this technology will enable the observations of EUV spectra from an entire 2D field of view in seconds, over two orders of magnitude faster than what is currently possible. The Spectral Imaging of the Solar Atmosphere (SISA) instrument is the first integral field spectrograph proposed for observations at ∼180 Å combining the image slicer technology and curved diffraction gratings in a highly efficient and compact layout, while providing important spectroscopic diagnostics for the characterisation of solar coronal and flare plasmas. SISA’s characteristics, main challenges, and the on-going activities to enable the image slicer technology for EUV applications are presented in this paper

Spectral Imager of the Solar Atmosphere: The First Extreme-Ultraviolet Solar Integral Field Spectrograph Using Slicers

© 2024 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).Particle acceleration, and the thermalisation of energetic particles, are fundamental processes across the universe. Whilst the Sun is an excellent object to study this phenomenon, since it is the most energetic particle accelerator in the Solar System, this phenomenon arises in many other astrophysical objects, such as active galactic nuclei, black holes, neutron stars, gamma ray bursts, solar and stellar coronae, accretion disks and planetary magnetospheres. Observations in the Extreme Ultraviolet (EUV) are essential for these studies but can only be made from space. Current spectrographs operating in the EUV use an entrance slit and cover the required field of view using a scanning mechanism. This results in a relatively slow image cadence in the order of minutes to capture inherently rapid and transient processes, and/or in the spectrograph slit ‘missing the action’. The application of image slicers for EUV integral field spectrographs is therefore revolutionary. The development of this technology will enable the observations of EUV spectra from an entire 2D field of view in seconds, over two orders of magnitude faster than what is currently possible. The Spectral Imaging of the Solar Atmosphere (SISA) instrument is the first integral field spectrograph proposed for observations at ∼180 Å combining the image slicer technology and curved diffraction gratings in a highly efficient and compact layout, while providing important spectroscopic diagnostics for the characterisation of solar coronal and flare plasmas. SISA’s characteristics, main challenges, and the on-going activities to enable the image slicer technology for EUV applications are presented in this paper.H.A.S.R. and S.A.M. were funded by the UK Science, Technology, and Facilities Council (STFC) under the consolidated grant ST/W001004/1. H.A.S.R. also acknowledges funding from STFC grant ST/X002012/1. G.D.Z. acknowledges support from STFC via the consolidated grants to the atomic astrophysics group at DAMTP, University of Cambridge (ST/P000665/1. and ST/T000481/1). J.D. acknowledges the Czech National Science Foundation, Grant No. GACR 22-07155S, as well as institutional support RWO:67985815 from the Czech Academy of Sciences. G.S.K. acknowledges financial support from NASA’s Early Career Investigator Program (Grant# NASA 80NSSC21K0460) as well as from the PHaSER cooperative agreement (80NSSC21M0180). D.O.S. acknowledges financial support from the grants AEI/MCIN/10.13039/501100011033/ (RTI2018-096886-C5, PID2021-125325OB-C5, PCI2022-135009-2) and ERDF “A way of making Europe” and “Center of Excellence Severo Ochoa” award to IAA-CSIC (CEX2021-001131-S). L.A.H. and S.M. are supported by ESA Research Fellowships. A.C.R. acknowledges the ETP funding programme of the UK Space Agency and Durham University Seedcorn Funding.With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2021-001131-S).Peer reviewe

The Solar Particle Acceleration Radiation and Kinetics (SPARK) Mission Concept

© 2023by the authors. Licensee MDPI, Basel, Switzerland. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY), https://creativecommons.org/licenses/by/4.0/Particle acceleration is a fundamental process arising in many astrophysical objects, including active galactic nuclei, black holes, neutron stars, gamma-ray bursts, accretion disks, solar and stellar coronae, and planetary magnetospheres. Its ubiquity means energetic particles permeate the Universe and influence the conditions for the emergence and continuation of life. In our solar system, the Sun is the most energetic particle accelerator, and its proximity makes it a unique laboratory in which to explore astrophysical particle acceleration. However, despite its importance, the physics underlying solar particle acceleration remain poorly understood. The SPARK mission will reveal new discoveries about particle acceleration through a uniquely powerful and complete combination of γ-ray, X-ray, and EUV imaging and spectroscopy at high spectral, spatial, and temporal resolutions. SPARK’s instruments will provide a step change in observational capability, enabling fundamental breakthroughs in our understanding of solar particle acceleration and the phenomena associated with it, such as the evolution of solar eruptive events. By providing essential diagnostics of the processes that drive the onset and evolution of solar flares and coronal mass ejections, SPARK will elucidate the underlying physics of space weather events that can damage satellites and power grids, disrupt telecommunications and GPS navigation, and endanger astronauts in space. The prediction of such events and the mitigation of their potential impacts are crucial in protecting our terrestrial and space-based infrastructure.Peer reviewe

The Solar Particle Acceleration Radiation and Kinetics (SPARK) mission concept

Particle acceleration is a fundamental process arising in many astrophysical objects, including active galactic nuclei, black holes, neutron stars, gamma-ray bursts, accretion disks, solar and stellar coronae, and planetary magnetospheres. Its ubiquity means energetic particles permeate the Universe and influence the conditions for the emergence and continuation of life. In our solar system, the Sun is the most energetic particle accelerator, and its proximity makes it a unique laboratory in which to explore astrophysical particle acceleration. However, despite its importance, the physics underlying solar particle acceleration remain poorly understood. The SPARK mission will reveal new discoveries about particle acceleration through a uniquely powerful and complete combination of γ-ray, X-ray, and EUV imaging and spectroscopy at high spectral, spatial, and temporal resolutions. SPARK’s instruments will provide a step change in observational capability, enabling fundamental breakthroughs in our understanding of solar particle acceleration and the phenomena associated with it, such as the evolution of solar eruptive events. By providing essential diagnostics of the processes that drive the onset and evolution of solar flares and coronal mass ejections, SPARK will elucidate the underlying physics of space weather events that can damage satellites and power grids, disrupt telecommunications and GPS navigation, and endanger astronauts in space. The prediction of such events and the mitigation of their potential impacts are crucial in protecting our terrestrial and space-based infrastructure