The MIT x-ray Polarimetry Beamline is a facility that we developed for testing components for possible use in x-ray polarimetry. Over the past few years, we have demonstrated that the x-ray source can generate nearly 100% polarized x-rays at various energies from 183eV (Boron Kα) to 705eV (Fe Lα) using a laterally graded multilayer coated mirror (LGML) oriented at 45 degrees to the source. The position angle of the polarization can be rotated through a range of roughly 150°. In a downstream chamber, we can orient a Princeton Instruments MTE1300B CCD camera to observe the polarized light either directly or after reflection at 45° by a second LGML. In support of the REDSoX Polarimeter project, we have tested four other detectors by directly comparing them to the PI camera. Two were CCD cameras: a Raptor Eagle XV and a CCID94 produced by MIT Lincoln Laboratories, and two had sCMOS sensors: the Sydor Wraith with a GSENSE 400BSI sensor and a custom Sony IMX290 sensor. We will show results comparing quantum efficiencies and event images in the soft x-ray band.
The Rocket Experiment Demonstration of a Soft X-ray Polarimeter (REDSoX) is a NASA-funded sounding rocket instrument that can make the first measurement of the linear X-ray polarization of an extragalactic source in the 0.2-0.4 keV band. We employ multilayer-coated mirrors as Bragg reflectors at the Brewster angle. By matching the dispersion of a dispersive spectrometer using critical angle transmission gratings to three laterally graded multilayer mirrors (LGMLs), we achieve polarization modulation factors over 90%. We will describe new prototyping work as well as extensions of the design for an orbital version.
This work is supported in part by NASA grant 80NSSC23K0644.
High resolving power soft x-ray spectroscopy has been confirmed by the recent Astro2020 Decadal Survey as a high-priority strategic goal with R =λ/Δλ as high as 7500 for some science cases. Examples are the characterization of highly ionized gases in galaxy halos and within and around galaxy clusters, accretion onto supermassive black holes, coronal mass ejections and coronal heating. Below the level of an expensive strategic mission, but far exceeding current capabilities, falls the Arcus Grating Explorer mission concept, with a minimum R of 2500 (expected R = 3500) and effective area up to ∼ 300 cm2 in the 12-50 Å bandpass. Arcus relies on light-weight, high-efficiency, blazed and alignment-insensitive critical-angle transmission (CAT) gratings for dispersion. The mission calls for hundreds of ∼ 30×30 mm2 gratings with a hierarchy of integrated support structures. The most recent CAT gratings have been fabricated from 200 mm silicon-on-insulator wafers using commercial, volume production compatible tools from the semiconductor and MEMS industries. We report x-ray results from quasifully illuminated, co-aligned CAT gratings showing record-high R ∼ 1.3×104 in 18th order at Al-Kα wavelengths, and diffraction efficiency of blazed orders in agreement with pencil beam synchrotron measurements and model predictions at O-K. Tilt of the deep-etched, freestanding grating bars relative to the grating surface is measured and successfully compensated through angular alignment during bonding of the Si gratings to metal frames. We also report on updates to the Arcus resolving power error budget, and on post-fabrication thinning of grating bars, which could lead to increased diffraction efficiency.
We describe an implementation of a broad-band soft X-ray polarimeter, substantially based on previous designs. The Globe-Orbiting Soft X-ray Polarimeter (GOSoX) is a SmallSat. As in a related mission concept the PiSoX Polarimeter, the grating arrangement is designed optimally for the purpose of polarimetry matching the dispersion of a spectrometer to a laterally graded multilayer (LGML). For GOSoX, the optics are lightweight Si mirrors in a one-bounce parabolic configuration. The instrument covers the wavelength range from 31 A to 75 A (165 - 400 eV). Upon satellite rotation, the intensities of the dispersed spectra, after reflection and polarizing by the LGMLs, give the three Stokes parameters needed to determine a source's linear polarization fraction and orientation. The design can be extended to higher energies as LGMLs are developed further. We describe the potential scientific return and the proposed mission concept following the results of a JPL Team X concept study.
The soft x-ray band covers the characteristic lines of the highly ionized low-atomic-number elements, providing diagnostics of the warm and hot plasmas in star atmospheres, interstellar dust, galaxy halos and clusters, and the cosmic web. High-resolution spectroscopy in this band is best performed with grating spectrometers. Soft x-ray grating spectroscopy with R = λ / Δ λ = > 104 has been demonstrated with critical-angle transmission (CAT) gratings. CAT gratings combine the relaxed alignment and temperature tolerances and the low mass of transmission gratings with high diffraction efficiency blazed in high orders. They are an enabling technology for the proposed Arcus grating explorer and were selected for the Lynx Design Reference Mission grating spectrometer instrument. Both Arcus and Lynx require the manufacture of hundreds to perhaps ~2000 large-area CAT gratings. We are moving toward CAT grating volume manufacturing using 200 mm silicon-on-insulator wafers, 4X optical projection lithography tools, deep reactive-ion etching, and KOH polishing. We have, for the first time, produced high-throughput 200 nm-period CAT gratings ~50% deeper than previously fabricated. X-ray diffraction efficiency is significantly improved in the ~1:25 - 1.75 nm wavelength range, peaking above 40% (sum of blazed orders). A new grating-to-grating alignment technique utilizing cross-support diffraction of visible light is presented, as well as the results of CAT grating emissivity measurements.λ
We present an update on our work measuring the performance and alignment of the critical-angle transmission (CAT) gratings for the proposed sounding Rocket Experiment Demonstration of a Soft X-ray Polarimeter (REDSoX) mission, as well as a possible orbital version. We built and verified a grating alignment system that could be used for REDSoX Polarimeter fabrication. The performances of the gratings were measured using the MIT polarimetry beamline. The beamline is a monochromator and has been used to measure the absolute efficiencies of not only the REDSoX prototype gratings but also the Arcus Phase A gratings. It is also capable of producing and measuring polarized soft X-rays to aid in the development and testing of future missions. Lastly, we present an update on our effort applying twisted crystals to X-ray polarimetry. Support for this work was provided in part by the NASA grant NNX15AL14G and a grant from the MIT Kavli Institute Research Investment Fund.
We describe a new implementation of a broad-band soft X-ray polarimeter, substantially based on a previous design. This implementation, the Pioneer Soft X-ray Polarimeter (PiSoX) is a SmallSat, designed for NASA’s call for Astrophysics Pioneers, small missions that could be CubeSats, balloon experiments, or SmallSats. As in REDSoX, the grating arrangement is designed optimally for the purpose of polarimetry with broad-band focussing optics by matching the dispersion of the spectrometer channels to laterally graded multilayers (LGMLs). The system can achieve polarization modulation factors over 90%. For PiSoX, the optics are lightweight Si mirrors in a one-bounce parabolic configuration. High efficiency, blazed gratings from opposite sectors are oriented to disperse to a LGML forming a channel covering the wavelength range from 35 Å to 75 Å (165 - 350 eV). Upon satellite rotation, the intensities of the dispersed spectra, after reflection and polarizing by the LGMLs, give the three Stokes parameters needed to determine a source’s linear polarization fraction and orientation. The design can be extended to higher energies as LGMLs are developed further. We describe examples of the potential scientific return from instruments based on this design.
X-ray polarimetry is still largely uncharted territory. With the upcoming launch of IXPE, we will learn a lot more about X-ray polarization at energies above 2 keV, but so far no current or accepted mission provides observational capabilities below 2 keV. We present ray-tracing results for a small orbital mission that could be launched within NASA’s Pioneer or SmallSat cost-cap to provide X-ray polarimetry below 2 keV. The design is based on the use of laterally-graded multi-layer (ML) mirrors, a concept that we have developed theoretically for the REDSoX Polarimeter,1 for which most components have been verified in the laboratory. In this contribution, we describe a single channel orbital mission based on the same idea, but modified to the unique cost and space requirements. All results scale up easily to two or more polarimetry channels. Scaling up would simply increase the effective area and reduce the need to rotate the instrument to measure the different polarization directions. In particular, we use the ray-traces to define the maximum size of the dispersion gratings and to determine an alignment budget.
We present the performance and recent results of the MIT polarimetry beamline. Originally designed for testing Chandra HETG gratings, the beamline has been adapted to test components for soft x-ray polarimetry applications. Since then, its monochromator capabilities have also been used to test gratings. We present results on the measured absolute efficiencies of the Arcus Phase A gratings using the B-K, O-K, and C-K emission lines. The beamline has also been used to develop tools and techniques to measure the linear polarization of soft X-rays (0.2-0.8 keV), which form the basis for a sounding rocket mission REDSoX (Rocket Experiment Demonstration of a Soft X-ray Polarimeter) and a possible orbital mission. We present our tests to align the REDSoX gratings, as well as our idea to use thin twisted crystals as a possible alternative to laterally-graded multilayer mirrors. Support for this work was provided in part by the NASA grant NNX15AL14G and a grant from the MIT Kavli Institute.
The Rocket Experiment Demonstration of a Soft X-ray Polarimeter (REDSoX Polarimeter) is a sounding rocket instrument that can make the first measurement of the linear X-ray polarization of an extragalactic source in the 0.2-0.5 keV band as low as 10%. We employ multilayer-coated mirrors as Bragg reflectors at the Brewster angle. By matching the dispersion of a dispersive spectrometer using critical angle transmission gratings to three laterally graded multilayer mirrors (LGMLs), we achieve polarization modulation factors over 90%. We will describe new prototyping work as well as extensions of the design for an orbital version.
This work was supported in part by NASA grants NNX15AL14G and NNX17AE11G to develop the design for a soft X-ray polarimeter.
MIRADAS (Mid-resolution InfRAreD Astronomical Spectrograph) is the facility near-infrared multi-object echelle spectrograph for the Gran Telescopio Canarias (GTC) 10.4-meter telescope. MIRADAS operates at spectral resolution R=20,000 over the 1-2.5µm bandpass), and provides multiplexing (up to N=12 targets) and spectro-polarimetry. The MIRADAS consortium includes the University of Florida, Universidad de Barcelona, Universidad Complutense de Madrid, Instituto de Astrofísica de Canarias, Institut d'Estudis Espacials de Catalunya and Universidad Nacional Autonoma de Mexico, as well as partners at A-V-S (Spain), New England Optical Systems (USA), and IUCAA (India). MIRADAS completed its Final Design Review in 2015, and in this paper, we review the current status and overall system design for the instrument, with scheduled delivery in 2018. We particularly emphasize key developments in cryogenic robotic probe arms for multiplexing, a macro-slicer mini-IFU, an advanced cryogenic spectrograph optical system, and a SIDECAR-based array control system for the 1x2 HAWAII-2RG detector mosaic.
CIRCE is a near-infrared (1-2.5 micron) imager (including low-resolution spectroscopy and polarimetery) in operation as a visitor instrument on the Gran Telescopio Canarias 10.-4m tele scope. It was built largely by graduate students and postdocs, with help from the UF Astronomy engineering group, and is funded by the University of Florida and the U.S. National Science Foundation. CIRCE is helping to fill the gap in time between GTC first light and the arrival of EMIR, and will also provide the following scientific capabilities to compliment EMIR after its arrival: high-resolution imaging, narrowband imaging, high-time-resolution photometry, polarimetry, and low-resolution spectroscopy. There are already scientific results from CIRCE, some of which we will review. Additionally, we will go over the observing modes of CIRCE, including the two additional modes that were added during a service and upgrading run in March 2016.
The Mid-resolution InfRAreD Astronomical Spectrograph (MIRADAS, a near-infrared multi-object echelle spectrograph operating at spectral resolution R=20,000 over the 1-2.5μm bandpass) was selected by the Gran Telescopio Canarias (GTC) partnership as the next-generation near-infrared spectrograph for the world's largest optical/infrared telescope, and is being developed by an international consortium. The MIRADAS consortium includes the University of Florida, Universidad de Barcelona, Universidad Complutense de Madrid, Instituto de Astrofísica de Canarias, and Institut d'Estudis Espacials de Catalunya, as well as probe arm industrial partner A-V-S (Spain), with more than 45 Science Working Group members in 10 institutions primarily in Spain, Mexico, and the USA. In this paper, we review the overall system design and project status for MIRADAS during its early fabrication phase in 2016.
We describe the design, development, and laboratory test results of cryogenic probe arms
feeding deployable integral field units (IFUs) for the Mid-resolution InfRAreD Astronomical
Spectrograph (MIRADAS) - a near-infrared multi-object echelle spectrograph for the 10.4-meter
Gran Telescopio Canarias. MIRADAS selects targets using 20 positionable pickoff mirror optics
on cryogenic probe arms, each feeding a 3.7x1.2-arcsec field of view to the spectrograph
integral field units, while maintaining excellent diffraction-limited image quality. The probe arms
are based on a concept developed for the ACES instrument for Gemini and IRMOS for TMT.
We report on the detailed design and opto-mechanical testing of MIRADAS prototype probe
arms, including positioning accuracy, repeatability, and reliability under fully cryogenic
operation, and their performance for MIRADAS. We also discuss potential applications of this
technology to future instruments.
CIRCE is a near-infrared (1-2.5 micron) imager, polarimeter and low-resolution spectrograph intended as a visitor instrument for the Gran Telescopio Canarias 10.-4m telescope. It was built largely by graduate students and postdocs, with help from the UF astronomy engineering group, and is funded by the University of Florida and the U.S. National Science Foundation. CIRCE is intended to help fill the gap in time between GTC first light and the arrival of EMIR, and will also provide the following scientific capabilities to compliment EMIR after its arrival: high- resolution imaging, narrowband imaging, high-time-resolution photometry, imaging- and spectro- polarimetry, low-resolution spectroscopy. In this poster, we review the lab testing results for CIRCE from 2013 and describe the instrument status (currently in shipment to GTC).
In this paper we present the results of image quality tests performed on the optical system of the Canarias InfraRed Camera Experiment (CIRCE), a visitor-class near-IR imager, spectrograph, and polarimeter for the 10.4 meter Gran Telescopio Canarias (GTC). The CIRCE optical system is comprised of eight gold-coated aluminum alloy 6061 mirrors. We present surface roughness analysis of each individual component as well as optical quality of the whole system. We found all individual mirror surface roughness are within specifications except Fold mirrors 1 and 2. We plan to have these components re-cut and re-coated. We used a flat 0.2-arcseconds pinhole mask placed in the focal plane of the telescope to perform the optical quality tests of the system. The pinhole mask covers the entire field of view of the instrument. The resulting image quality allows seeing-limited performance down to seeing of 0.3 arcseconds FWHM. We also observed that our optical system produces a negative field curvature, which compensates the field curvature of the Ritchey-Chretien GTC design once the instrument is on the telescope.
The Mid-resolution InfRAreD Astronomical Spectrograph (MIRADAS, a near-infrared multi-object echelle
spectrograph operating at spectral resolution R=20,000 over the 1-2.5μm bandpass) was selected in 2010 by the Gran
Telescopio Canarias (GTC) partnership as the next-generation near-infrared spectrograph for the world's largest
optical/infrared telescope, and is being developed by an international consortium. The MIRADAS consortium includes
the University of Florida, Universidad de Barcelona, Universidad Complutense de Madrid, Instituto de Astrofísica de
Canarias, Institut de Física d'Altes Energies, Institut d'Estudis Espacials de Catalunya and Universidad Nacional
Autonoma de Mexico, as well as probe arm industrial partner A-V-S (Spain). In this paper, we review the overall system
design for MIRADAS, as it nears Preliminary Design Review in the autumn of 2012.
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