Extreme Ultraviolet X-ray Research Articles

X-ray/Extreme Ultraviolet Floquet State Multidimensional Spectroscopy, an Analogue of Multiple Quantum Nuclear Magnetic Resonance

There is great interest in developing fully coherent multidimensional X-ray/extreme ultraviolet (XUV) spectroscopic techniques because of their capability for achieving atomic spectral selectivity. Current proposals rest on using sequentially and coherently driven core excitations with multiple X-ray/XUV excitation pulses and measuring the output using time domain Fourier transform methods. In this paper, we propose an alternative method that creates an entanglement of core and optical transitions to form a Floquet state that creates directional and coherent output beams. Multidimensional spectra are obtained by measuring the intensity of output beams while tuning the optical frequencies across resonances. This approach expands on previous optical pump-XUV probe spectroscopy of MoTe2 by theoretically demonstrating its multidimensional capabilities. Both parametric and non-parametric pathways are proposed to optimize the resolution of inhomogeneous broadening and k-selective features.

Stellar rotation and its connection to the evolution of hydrogen‐dominated atmospheres of exoplanets

AbstractThe population of known low‐ to intermediate‐mass exoplanets shows a large spread in densities, which is believed to be due to the diversity of planetary atmospheres and thus controlled by planetary atmospheric mass loss. One of the main drivers of long‐term atmospheric escape is the absorption of high‐energy X‐ray + extreme ultraviolet (XUV) radiation from the host star. For main sequence solar‐like stars, rotation and XUV radiation are closely connected, with faster rotating stars being XUV brighter and with both rotation and XUV decreasing with time. This evolution, however, does not follow a unique path, as stars born with the same mass and metallicity can have widely different initial rotation rates. This nonuniqueness holds up to about 1 Gyr, while atmospheric escape from exoplanets is strongest. The atmospheric mass loss through this period is often deciding the future of the planet and its position in the observed population. Therefore, the diversity of possible stellar histories can be an uncertain factor affecting the predictions of population studies. Here, I explore its relevance for different planets and different host stars.

A High-Precision Flat Field Method Based on Image Stitching for Short Wavelength Instruments

We present a method to obtain a large-scale flat field using only small offsets. The method is derived from the Kuhn, Lin, and Loranz (KLL) algorithm (Publ. Astron. Soc. Pacific103, 1097, 1991), but combined with the image stitching technique. Due to complementary images, which optimize and replace the bad edges, the accuracy is better than 0.1 root mean square across the full field of view, and the pixel-level relative error is also better than 0.1%. Another significant advantage is that its small sampling interval provides a rapid sampling time, while maintaining a large-scale and high-precision flat field (beyond 95% proportion). We have proved its high efficiency and robustness by simulating a cosine and a Gaussian CCD response and comparing the results with the KLL algorithm. Finally, a visible non-uniform target experiment with a uniform response was performed to prepare for the upcoming solar X-ray Extreme Ultraviolet Imager (X-EUVI) instrument on the FengYun-3 (FY-3) weather satellite series.

Habitable evaporated cores: transforming mini-Neptunes into super-Earths in the habitable zones of M dwarfs.

We show that photoevaporation of small gaseous exoplanets ("mini-Neptunes") in the habitable zones of M dwarfs can remove several Earth masses of hydrogen and helium from these planets and transform them into potentially habitable worlds. We couple X-ray/extreme ultraviolet (XUV)-driven escape, thermal evolution, tidal evolution, and orbital migration to explore the types of systems that may harbor such "habitable evaporated cores" (HECs). We find that HECs are most likely to form from planets with ∼1 M⊕ solid cores with up to about 50% H/He by mass, though whether or not a given mini-Neptune forms a HEC is highly dependent on the early XUV evolution of the host star. As terrestrial planet formation around M dwarfs by accumulation of local material is likely to form planets that are small and dry, evaporation of small migrating mini-Neptunes could be one of the dominant formation mechanisms for volatile-rich Earths around these stars.

Ionization dynamics in expanding clusters studied by XUV pump–probe spectroscopy

The expansion and disintegration dynamics of xenon clusters initiated by the ionization with femtosecond soft x-ray extreme ultraviolet (XUV) pulses were studied with pump–probe spectroscopy using the autocorrelator setup of the Free-Electron LASer in Hamburg (FLASH) facility. The ionization by the first XUV pulse of 92 eV photon energy (8 × 1012 W cm−2) leads to the generation of a large number of quasi-free electrons trapped by the space charge of the cluster ions. A temporally delayed, more intense probe (4 × 1013 W cm−2) pulse substantially increases a population of nanoplasma electrons providing a way of probing plasma states in the expanding cluster by tracing the average charge of fragment ions. The results of the study reveal a timescale for cluster expansion and disintegration, which depends essentially on the initial cluster size. The average charge state of fragment ions, and thus the cluster plasma changes significantly on a timescale of 1–3 ps.

The measurement of the intrinsic impurities of molybdenum and carbon in the Alcator C-Mod tokamak plasma using low resolution spectroscopy

The intrinsic impurity content of molybdenum and carbon was measured in the Alcator C-Mod tokamak using low resolution, multilayer mirror (MLM) spectroscopy ( Delta lambda ~1-10 AA). Molybdenum was the dominant high-Z impurity and originated from the molybdenum armour tiles covering all of the plasma facing surfaces (including the inner column, the poloidal divertor plates and the ion cyclotron resonant frequency (ICRF) limiter) at Alcator C-Mod. Despite the all metal first wall, a carbon concentration of 1 to 2% existed in the plasma and was the major low-Z impurity in Alcator C-Mod. Thus, the behaviour of intrinsic molybdenum and carbon penetrating into the main plasma and the effect on the plasma must be measured and characterized during various modes of Alcator C-Mod operation. To this end, soft X-ray extreme ultraviolet (XUV) emission lines of charge states, ranging from hydrogen-like to helium-like lines of carbon (radius/minor radius, r/a~1) at the plasma edge to potassium to chlorine-like (0.4<r/a<0.6) and magnesium- to sodium-like (r/a<0.4) lines of molybdenum in the main plasma, were measured using a novel, low resolution, photometrically calibrated polychromator with MLMs as dispersive elements. The MLM spectra were investigated in detail, and comparisons with high resolution spectroscopy were made. The utility of low resolution spectroscopy to diagnose tokamak plasmas is presented, and meaningful information about impurity behaviour was obtainable owing to the specific choice of the observed spectral regions. Ab initio physics rates from the HULLAC atomic physics package were input into the collisional radiative (CR) model and the multiple ionization state transport (MIST) code, and both MIST and the CR model were used in the interpretation of the molybdenum spectrum. The carbon spectrum was interpreted using the MIST code and the direct impact rates of Itikawa (Itakawa, Y., et al., At Data Nucl. Data Tables 33 (1985) 149), which were incorporated into the collisional radiative model. The intrinsic i

Survey of Ti-, B-, and Y-based soft x-ray–extreme ultraviolet multilayer mirrors for the 2- to 12-nm wavelength region

We have performed an experimental investigation of Ti-, B(4)C-, B-, and Y-based multilayer mirrors for the soft x-ray¿extreme ultraviolet (XUV) wavelength region between 2.0 and 12.0 nm. Eleven different material pairs were studied: Ti/Ni, Ti/Co, Ti/Cu, Ti/W, B(4)C/Pd, B/Mo, Y/Pd, Y/Ag, Y/Mo, Y/Nb, and Y/C. The multilayers were sputter deposited and were characterized with a number of techniques, including low-angle x-ray diffraction and normal incidence XUV reflectometry. Among the Ti-based multilayers the best results were obtained with Ti/W, with peak reflectances up to 5.2% at 2.79 nm at 61° from normal incidence. The B(4)C/Pd and B/Mo multilayer mirrors had near-normal incidence (5°) peak reflectances of 11.5% at 8.46 nm and 9.4% at 6.67 nm, respectively, whereas a Y/Mo multilayer mirror had a maximum peak reflectance of 25.6% at 11.30 nm at the same angle. The factors limiting the peak reflectance of these different multilayer mirrors are discussed.

Multi-Spectral Solar Telescope Array

The development of multilayer optics has profound implications for soft x-ray/extreme ultraviolet (XUV) astronomy. During the October 1987 flight of the Stanford/Marshall Space Flight Center Rocket X-Ray Spectroheliograph, narrow wavelength band, low scatter soft x-ray/extreme ultraviolet spectroheliograms were obtained with -1 arcsec spatial resolution at X - 173 A (Fe IX, Fe X) and at is. - 256 A (He II Ly-3). Although the Cassegrain telescopes used in this experiment were small (63.5 mm diameter) and utilized spherical rather than paraboloidal/hyperboloidal mirrors, the images produced exceed in quality any XUV spectroheliograms previously obtained with either normal or grazing incidence techniques. We describe a new rocket spectroheliograph instrument, the Multi- Spectral Solar Telescope Array (MSSTA), that is currently being prepared for launch in August 1990. This instrumentwill utilizetrue Ritchey-Chrétien optics of 127 mm diameter and parabolic Herschelian optics of 40 mm diameter, which will allow spectroheliograms to be obtained over the soft x-ray/extreme ultraviolet/far ultraviolet spectral range (40 to 1550 A). The performance of this new instrument should definitely demonstrate the unique combination of ultrahigh spatial resolution and spectral differentiation that multilayer optics afford for astronomical observations. The MSSTA will also represent the first astronomical use of an important new optical device, the multilayer grating. The MSSTA should obtain unprecedented information regarding the structure and dynamics of the solar atmosphere in the temperature range i04 to i07 K.

An Overview of the Orbiting Solar Laboratory

AbstractThe Orbiting Solar Laboratory (OSL), which is a joint NASA/BMFT/ASI/ AFGL program, will be a free flying, polar orbiting complement of five scientific instruments operating as a facility and designed to observe the surface and upper atmosphere of the sun with high spatial and temporal resolution over a spectral range from the soft X-ray to the near Infrared. OSL’s primary scientific objectives are to study the coupling of velocity, magnetic, and radiation fields in the photosphere and chromosphere and to causally relate this coupling to activity in the overlying regions.To study the photosphere and chromosphere with a spatial resolution approaching 75 km OSL will utilize a 1 meter telescope, optimized for 2000–11,000 Å, to feed a narrow band tunable filter, a set of fixed broad-band filters, and a spectrograph. These three instruments share a common structure, share a unified science data and control system, and use a single-image stabilization system for their common fields of view to form a Coordinated Instrument Package (CIP). To study the transition zone a stigmatic High Resolution Telescope Spectrograph (HRTS) optimized for 1175–1700 Å, will be used capable of providing both images and spectroscopic information. A X-Ray Extreme Ultraviolet Imager and Spectroheliograph (XUVI) optimized for the 40–400 Å regime, will allow study of the corona and of multimillion degree solar transient events such as flares. Both the HRTS and the XUVI instruments will possess image stabilization systems and have a resolving power of 350 km. All OSL instruments will operate overlapping fields of view and be co-aligned. To achieve its goals the OSL will provide a total data stream of 20 M bits/s, nominally 4 M bits/s per instrument and has a planned operational lifetime of three years.