Mg/SiC multilayer coatings with Al-Mg corrosion barrier layers and with high reflectance in up to three narrow
wavelength bands within the 25-80 nm wavelength region have been developed for EUV laser source applications. The
physics of the spontaneous intermixing and amorphization of the Al-Mg corrosion barriers for Mg/SiC multilayers are
currently being investigated in detail. Initial results from studies of the long-term reflectance properties of corrosionresistant
Mg/SiC multlayers are also discussed.
We present several concept designs of hard X-ray/soft λ-ray focusing telescopes for future astrophysics missions. The designs are based on depth graded multilayer coatings. These have been successfully employed on the NuSTAR mission for energies up to 80 keV. Recent advances in demonstrating theoretical reflectivities for candidate multilayer material combinations up to 400 keV including effects of incoherent scatter has given an experimental base for extending this type of designs to the soft λ-ray range. At the same time, the calibration of the in-flight performance of the NuSTAR mission has given a solid understanding and modelling of the relevant effects influencing the performance, including optical constants, roughness, scatter, non-uniformities and figure error. This allows for a realistic extension for designs going to much higher energies. Similarly, both thin slumped glass and silicon pore optics has been developed to a prototype stage which promises imaging resolution in the sub 10 arcsecond range. We present designs based on a 20 m and 50 m focal lengths with energy ranges up to 200 keV and 600 keV.
This manuscript presents an overview of recent work performed on x-ray optics development, metrology and calibration for the Soft X-ray Research (SXR) and the Coherent X-ray Imaging (CXI) instruments at the Linac Coherent Light Source (LCLS) free-electron laser. We also present results on the first LCLS exposures of boron carbide (B4C)-coated samples at photon energies near the carbon K edge and discuss relevant analysis and implications for future experiments.
The Bragg Reflection Polarimeter (BRP) on the NASA Gravity and Extreme Magnetism Small Explorer Mission is designed to measure the linear polarization of astrophysical sources in a narrow band centered at about 500 eV. X-rays are focused by Wolter I mirrors through a 4.5 m focal length to a time projection chamber (TPC) polarimeter, sensitive between 2{10 keV. In this optical path lies the BRP multilayer reflector at a nominal 45 degree incidence angle. The reflector reflects soft X-rays to the BRP detector and transmits hard X-rays to the TPC. As the spacecraft rotates about the optical axis, the reflected count rate will vary depending on the polarization of the incident beam. However, false polarization signals may be produced due to misalignments and spacecraft pointing wobble. Monte-Carlo simulations have been carried out, showing that the false modulation is below the statistical uncertainties for the expected focal plane offsets of <~ 2 mm.
A soft X-ray, beam-splitting, multilayer optic has been developed for the Bragg Reflection Polarimeter on the NASA Gravity and Extreme Magnetism Small Explorer Mission (GEMS). The optic is designed to reflect 0.5 keV X-rays through a 90 degree angle to the BRP detector, and transmit 2-10 keV X-rays to the primary polarimeter. A transmission requirement prevents the use of a thick substrate, so a 2 µm thick polyimide membrane was used. Atomic force microscopy has shown the membrane to possess high spatial frequency roughness less than 0.2 nm rms, permitting adequate X-ray reflectance. A multilayer thin film was especially developed with reflectance and transmission properties that satisfy the BRP requirements and with near-zero stress. Multilayer depositions for prototype reflectors have been performed via magnetron sputtering. Reflectivity and transmission measurements closely match theoretical predictions, both before and after rigorous environmental testing.
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.
Experimental multilayer reflectance data on flight mirrors and witnesses for three extreme ultraviolet (EUV) channels of
the Atmospheric Imaging Assembly (AIA) instrument aboard NASA’s Solar Dynamics Observatory are presented and
compared to theoretical models. The relevance of these results to the performance of the AIA instrument is discussed.
The corrosion mechanisms in Mg/SiC multilayers have been elucidated and corrosion-resistant Mg/SiC multilayer coatings have been demonstrated using spontaneously intermixed Al-Mg corrosion barrier layers. The corrosion-resistant Mg/SiC multilayers can achieve high reflectance simultaneously in up to three narrow wavelength bands within the 25-80 nm wavelength region, making them attractive candidates for solar physics instrumentation and for other applications.
NuSTAR is a hard X-ray satellite experiment to be launched in 2012. Two optics with 10.15 m focal length focus Xrays
with energies between 5 and 80 keV onto CdZnTe detectors located at the end of a deployable mast. The FM1 and
FM2 flight optics were built at the same time based on the same design and with very similar components, and thus the
performance of both is expected to be very similar. We provide an overview of calibration data that is being used to
build an optics response model for each optic and describe initial results for energies above 10 keV from the ground
calibration of the flight optics. From a preliminary analysis of the data, our current best determination of the overall
HPD of both the FM1 and FM2 flight optics is 52", and nearly independent of energy. The statistical error is negligible,
and a preliminary estimate of the systematic error is of order 4". The as-measured effective area and HPD meet the toplevel
NuSTAR mission sensitivity requirements.
This manuscript presents a first study of the contamination observed on some of the x-ray mirrors for the Linac Coherent
Light Source (LCLS) free-electron laser, the implications to the mirror lifetime properties and an evaluation of candidate
techniques towards successful recovery of these B4C- and SiC-coated mirrors. Initial experimental results and plans for
upcoming mirror recovery experiments are discussed. A summary of experimentally determined FEL damage thresholds
of B4C and SiC materials is also given, and their wavelength dependence is discussed.
We present the development of novel coatings for the far and extreme ultraviolet (FUV-EUV). In the EUV above ~50
nm, the strong absorption of materials has precluded the development of narrowband coatings. An extensive research has
been performed on the search and characterization of new materials with low absorption; the lanthanide series has been
found to be a source of materials with relatively low absorption in the range of interest. The discovery of a wealth of
materials with relatively low EUV absorption is basic to develop efficient multilayers, particularly with narrowband
properties. In this way, we have developed multilayers based on Yb, Al, and SiO with narrowband performance in the
50-92 nm range; these are first narrowband coatings peaked above 70 nm. Our recent research on multilayers based on
Eu, Al, and SiO provide promising results, with an increase in the peak reflectance versus Yb/Al/SiO multilayers, along
with a peak wavelength that can be extended up to ~100 nm.
For applications where FUV-EUV narrowband coatings have not been able to be prepared, we can design multilayers
that address specific purposes, such as maximizing the reflectance ratio at two wavelengths or bands. Our first goal in
this direction is the development of coatings with high 102.6 nm/ 121.6 nm reflectance ratio. Calculations predict that a
high reflectance at Lyman β with a good rejection at Lyman α can be obtained through multilayer coatings. We are at the
beginning of experimental research for this goal.
The spectral range of 50 to 115 nm in the extreme ultraviolet (EUV) is characterized by the high absorption and low
normal incidence reflectance of most materials, which make difficult the development of high reflectance multilayer
mirrors at normal incidence angles. The availability of efficient mirrors would have a great impact on the performance of
EUV space telescopes and other EUV instruments at these wavelengths. In order to obtain high normal-incidence
reflectance coatings, it is necessary to find materials with absorption as low as possible at 50 - 115 nm. Recently,
lanthanides and close elements have attracted the attention of researchers because of their relatively low absorption at
bands in the EUV, and several studies on the optical constants of lanthanides in the EUV have been published. As a
result of these investigations we have identified those lanthanides which better match the low absorption requirement at
wavelengths in the 50 - 115 nm range. In this work we present the use of the lanthanide Yb combined with other
materials and protective capping layers in multilayers designed to have a reflectance maximum at a wavelength selected
within the spectral range of 50 to 95 nm. Experimental results for the case of a multilayer composed of Yb, Al and SiO
layers confirm the adequacy of this approach, providing a peak reflectance of 0.276 at 80 nm with FWHM of 14.5 nm
for samples not exposed to the atmosphere. A decrease in peak reflectance from 0.276 to 0.209 was observed after 2
years of storage in a dessicator.
A summary of the research performed on the optical characterization of Sc and of several lanthanides from the visible to
the soft x-rays is presented. The low absorption of these materials mainly below the O2,3 edge (L2,3 edge for Sc) turns
them promising materials for the realization of multilayer mirrors in a spectral range in which most materials in nature
absorb strongly. Thin-film samples with several thicknesses of the target material were deposited by evaporation over
thin-film substrates in UHV, and their transmittance was measured in situ. A wide spectral range of direct
characterization, along with extrapolations to longer and shorter wavelengths either using literature data (when available)
or model predictions, enabled the development of consistent optical constants over the whole spectrum. An assortment of
consistency sum rules has been used, and it was found that each of them highlights a given spectral range, which may
help evaluate the consistency of each part of the combined spectrum.
The extinction coefficient of Pr, Eu and Tm thin films prepared by evaporation in ultra high vacuum has been obtained in the spectral ranges 4-1600, 8.3-1400 and 10-1400 eV, respectively. These data were calculated from experimental values of the transmittance of the films performed in situ, which means that the samples were not exposed to the atmosphere before and during their characterization. Several films of increasing thickness were deposited onto grids coated with a thin C support film. The results show that Pr, Eu and Tm, similar to other lanthanides, have a lowabsorption band right below the O2,3 edge onset, with lowest absorption measured at about 16.9, 16.7 and 23 eV, respectively. Therefore, these materials are promising for filters and multilayer coatings in the energy range below O2,3 edge in which materials typically present a strong absorption. In the cases of Pr and Eu the sum rule was applied to the extinction coefficient data in the whole spectrum, that included the current data along with those of the literature and extrapolations. The obtained values of the number of electrons contributing to the optical properties of the materials were close to predictions, which shows the consistency of current data. In the case of Pr, the real part of the index of refraction was also calculated through the Kramers-Kronig analysis, and the consistency of the results was assessed by means of the inertial sum rule.
A summary of the optical coatings for the spectral range from 50 to 200 nm that can be prepared at GOLD is presented.
This spectral range, named here far and extreme ultraviolet (FUV/EUV), is characterized by the high absorption of
almost all materials and the strong dependence of their optical properties on the deposition parameters and on the
exposure of the samples to the atmosphere. Broadband mirrors and narrowband filters were prepared in an ultra high
vacuum system where in situ FUV/EUV reflectometry is available. In this work we summarize the main aspects
concerning in situ performance and ageing of these coatings. Broadband mirrors composed of Al/MgF2, SiC, B and
Al/MgF2/SiC cover the FUV/EUV spectral range from 50 to 200 nm. Above the transparency cutoff of MgF2 (115 nm),
transmittance filters based on Al/MgF2 multilayers have been developed peaked at wavelengths as short as 120 nm. An
example is shown centered at 124 nm with a peak transmittance of 27% and a FWHM of 12 nm for a fresh coating.
Below 115 nm, a research on reflectance filters has recently started with very promising results on filters peaked at ~83
nm, close to the OII spectral line. Fresh filters with 27% peak reflectance at normal incidence and a FWHM of 14 nm
have been obtained. These novel reflectance filters based on Al, Yb and SiO must still demonstrate stability over time.
The developed coatings have a potential application in the field of astronomical observations.
The transmittance of thin films of Yb deposited by evaporation in ultra high vacuum (UHV) conditions have been investigated in the 23-1,700 eV spectral range. Transmittance measurements were performed in situ on Yb films deposited over grids coated with a thin, C support film. Transmittance measurements were used to obtain the extinction coefficient of Yb films at each individual photon energy investigated. The energy range investigated encompasses M, N, and O edges of Yb. The current results, along with data in the literature, show that Yb has an interesting low-absorption band in the ~12-24 eV range. The promising characteristics of Yb as a filter material in this region requires the development of a protection material due to the reactivity of Yb under normal atmosphere. The low absorption of Yb in the above range makes it also a candidate for a component of multilayer coatings in a spectral region in which few developments have been performed due to the lack of low absorption materials. The fl sum-rule was applied to extinction coefficient data in the whole spectrum that included the current data along with those of the literature, resulting in a value of 70.26, which is close to the expected value of 69.32.
The research on rare earths conducted by the current team addresses in this proceeding the transmittance measurement of
Ce films. Several thin films of Ce were deposited by evaporation in ultra high vacuum (UHV) conditions and their
transmittance was measured in situ in the 6-1,200 eV spectral range. Ce films were deposited onto grids coated with a
thin, C support film. Transmittance measurements were used to obtain the extinction coefficient of Ce films at each
individual photon energy investigated. Literature data for Ce films had been restricted to some parts of the current range,
with various experimental data at the strong N edge, a single set of data at the M edge, and no data at the O edge. The
energy range here investigated provides data encompassing M, N, and O edges of Ce, and this data set is extended
towards smaller energies with experimental data and towards larger energies with semi-empirical data and calculations.
Ce, as has been measured with other lanthanides, has a low-absorption band right below the O edge, with lowest
absorption at 16.1 eV. This makes Ce a promising material for filters and multilayer coatings in this spectral range, in
which few developments have been performed due to the lack of low absorption materials. The f1 sum-rule was applied
to the extinction coefficient data in the whole spectrum that included the current data along with those of the literature,
resulting in a value close to predictions, which shows the consistency of the current data.
This proceeding reviews the performance of a far-extreme ultraviolet (FUV-EUV) reflectometer-deposition system available at GOLD-Instituto de Fisica Aplicada, CSIC and the different sorts of coatings for the EUV that can be prepared with this equipment. Coatings both for wavelengths longer and shorter than the LiF/MgF2 cutoff wavelengths are prepared. Regarding coatings above these cutoffs, they are based in the combination of Al and MgF2. High reflectance coatings of Al protected with MgF2 can be prepared with a reflectance of ~80% at the H Lyman α line at 121.6 nm. Narrowband transmittance filters based on (Al/MgF2)n are also deposited, with a high peak transmittance down to wavelengths as short as 121.6 nm. Regarding coatings for wavelengths shorter than the fluoride cutoffs, wideband reflective coatings based on a single layer of SiC and also on Al/MgF2/SiC multilayers are prepared with a high reflectance at wavelengths longer than ~80 nm. In addition to the above coatings, a plan for the deposition in the near future of narrowband reflective coatings tuned at wavelengths as long as 95 nm (but shorter than the LiF cutoff) is discussed.
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