Dennis Stanley Martinez-Galarce

Multisegmented, multilayer-coated mirrors for the Solar Ultraviolet Imager

Abstract. The Solar Ultraviolet Imager (SUVI) is one of the several instruments that will fly on board the next generation of Geostationary Operational Environmental Satellites R-U platforms, as part of the National Oceanic and Atmospheric Administration’s space weather monitoring fleet. SUVI is a generalized Cassegrain telescope that employs multilayer-coated optics that operate in six extreme ultraviolet (EUV) narrow bandpasses centered at 93.9, 131.2, 171.1, 195.1, 284.2 and 303.8 Å. The innovation of the design is that SUVI is the first EUV solar telescope that has six different wavelength channels accommodated on each mirror. And despite having six segmented multilayer-coatings, shadowing (due to the mask) is minimized allowing SUVI to exceed its effective area specifications. Once operational, SUVI will record full-disk, spectroheliograms every few minutes, where this data will be used to better understand the effects of solar produced EUV radiation on Earth and the near-Earth environment. The material presented discusses general aspects of the SUVI optical design, mirror fabrication, super polishing, and metrology carried out to verify optical surface quality and in-band, EUV reflectivity performance of the multilayer coatings. The power spectral density and EUV measurements are shown to exceed performance requirements and are critical for the overall calibration and monitoring of SUVI’s throughput and imaging performance, once operational.

Review of substrate materials, surface metrologies and polishing techniques for current and future-generation EUV/x-ray optics

This manuscript presents a review of recent advances in EUV/x-ray substrate specification, fabrication and metrology for photolithography, synchrotron sources, free-electron laser sources, solar physics and astronomy. Highlights from ultra-low- expansion glass substrates, silicon and silicon carbide substrates are presented. Selected emerging substrate materials and fabrication technologies are also discussed.

Microroughness measurements and EUV calibration of the solar ultraviolet imager multilayer-coated mirrors

The Solar Ultraviolet Imager (SUVI) is one of several instruments that will fly on board the next generation of Geostationary Operational Environmental Satellites (GOES) -R and -S platforms, as part of NOAAs space weather monitoring fleet. SUVI is a Generalized Cassegrain telescope that employs multilayer-coated optics that operate in six extreme ultraviolet (EUV) narrow bandpasses centered at 93.9, 131.2, 171.1, 195.1, 284.2 and 303.8 Å. Once operational, over the mission lifetime expected to last up to 10 years, SUVI will record full disk, EUV spectroheliograms every few minutes, where this data will be used to better understand the effects of solar produced EUV radiation on Earth and the near-Earth environment. The material presented herein will touch upon general aspects of the SUVI optical design, as well as the fabrication, super polishing and metrology of the fabricated mirrors, including measured EUV spectral performance.

Performance of the multilayer-coated mirrors for the MultiSpectral Solar Telescope Array

The Multi-Spectral Solar Telescope Array, a rocket-borne solar observatory, was successfully flown in May, 1991, obtaining solar images in eight XUV and FUV bands with 12 compact multilayer telescopes. We report on recent measurements of the performance of multilayer coated mirrors for the Multi Spectral Solar Telescope Array, carried out at the Stanford Synchrotron Radiation Laboratory.

The high-resolution lightweight telescope for the EUV (HiLiTE)

The High-resolution Lightweight Telescope for the EUV (HiLiTE) is a Cassegrain telescope that will be made entirely of Silicon Carbide (SiC), optical substrates and metering structure alike. Using multilayer coatings, this instrument will be tuned to operate at the 465 Å Ne VII emission line, formed in solar transition region plasma at ~500,000 K. HiLiTE will have an aperture of 30 cm, angular resolution of ~0.2 arc seconds and operate at a cadence of ~5 seconds or less, having a mass that is about 1/4 that of one of the 20 cm aperture telescopes on the Atmospheric Imaging Assembly (AIA) instrument aboard NASAs Solar Dynamics Observatory (SDO). This new instrument technology thus serves as a path finder to a post-AIA, Explorer-class missions.

Phonon-mediated superconducting transition-edge sensor x-ray detectors for use in astronomy

In this paper we present preliminary work on a spatial, arrival time and energy resolving x-ray detector for the study of magnetic reconnection in the solar corona. Our detectors are cryogenic phonon-mediated superconducting Transition-Edge Sensors (TESs). X-rays are incident on a silicon substrate; the generated phonons propagate to the opposite side of the substrate and are absorbed in the tungsten TES electron system. Through a novel spatial distribution of four TESs we aim to achieve simultaneous measurement resolutions of ~10 μm, sub μs, and ~4 eV and with count rates of ~1 kHz. This four TES system is described and preliminary data obtained with a prototype two-channel detector is presented.

Design and performance of thin foil XUV filters for the Multi-Spectral Solar Telescope Array II

The redesigned payload of the Multi-Spectral Solar Telescope Array (MSSTA), the MSSTA II, was successfully flown on November 3, 1994. The multilayer mirrors used in the normal incidence optical systems of the MSSTA II are efficient reflectors for soft x-ray/extreme ultraviolet (EUV) radiation at wavelengths that satisfy the Bragg condition, thus allowing a narrow band of the soft x-ray/EUV spectrum to be isolated. When applied to solar observations the temperature response of an optical system is quite sensitive to telescope bandpass because of the high density of lines in the coronal spectrum. We have designed a set of thin foil filters in conjunction with our multilayer optics to eliminate contaminant lines and specular reflectivity, thus enhancing the temperature diagnostic capabilities of our instruments. Extensive measurements have recently been carried out on the thin foil filters at the Stanford Synchrotron Radiation Laboratory. We describe here the design and performance of thin foil filters developed for the MSSTA II.

High-resolution imaging with multilayer telescopes: resolution performance of the MSSTA II telescopes

The Multi-Spectral Solar Telescope Array (MSSTA) is a sounding rocket-borne observatory composed of a set of normal-incidence multilayer-coated telescopes that obtained selected bandpass spectroheliograms of the Solar atmosphere. These spectroheliograms were recorded on specially fabricated XUV and FUV 70mm Kodak film. Rocket launches of this instrument payload took place in 1991 and 1994 at the White Sands Missile Test Range in New Mexico, sponsored by the NASA sounding rocket experiment program. Immediately prior to the 1994 launch, visible light focusing test of each telescope were performed in-situ using a 1951 Standard Air Force High Resolution Test-target, to measure optical resolution performance. We determined that the MSSTA II telescopes performed at diffraction-limited resolutions down to 0.70 arc-second at visible wavelengths. Based on these measurements, we calculated an upper-bound to the focusing errors that incorporate the sum of all uncorrelated system resolution errors that affect resolution performance. Coupling these upper-bound estimates with the in-band diffraction limits, surface scattering errors and payload pointing jitter, we demonstrate that eleven of nineteen MSSTA II telescopes - having negligible figures of focus errors in comparison to the corresponding visible diffraction limits - performed at sub arc-second resolution at their operation FUV/EUV/XUV wavelengths during flight. We estimate the in-band performance down to 0.14 +/- 0.08 second of arc.

Chromospheric/coronal spectroheliograph

We describe a new payload, the Chromospheric/Coronal Spectroheliograph (CCS), that is optimized for the study of the chromospheric/coronal interface and the search for the sources of energy that sustain the quiescent solar atmosphere. We will utilize the existing optical bench, electronics, and some imaging system from the inventory of multilayer telescopes built up in our previous successful rocket flights of the Multi-Spectral Telescope Array. We will develop several new optical systems to explore more fully the thermal structure of the transition region and introduce a multilayer grating spectroheliograph to permit a more precise determination of the temperature of the structures that control the flow of energy between the chromosphere and the corona.

Recent developments in transition-edge strip detectors for solar x-rays

LMSAL and NIST are developing position-sensitive x-ray strip detectors based on Transition Edge Sensor (TES) microcalorimeters optimized for solar physics. By combining high spectral (E/ΔE ~1600) and temporal (single photon Δt ~10μs) resolutions with imaging capabilities, these devices will be able to study high-temperature (>10 MK) x-ray lines as never before. Diagnostics from these lines should provide significant new insight into the physics of both microflares and the early stages of flares. Previously, the large size of traditional TESs, along with the heat loads associated with wiring large arrays, presented obstacles to using these cryogenic detectors for solar missions. Implementing strip detector technology at small scales, however, addresses both issues: here, a line of substantially smaller effective pixels requires only two TESs, decreasing both the total array size and the wiring requirements for the same spatial resolution. Early results show energy resolutions of Δ ΕFWHM ~30eV and spatial resolutions of ~10-15 μm, suggesting the strip-detector concept is viable.