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Kyriacos Kalli - One of the best experts on this subject based on the ideXlab platform.
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Femtosecond Laser Written Plane-by-Plane Bragg Grating Sensors in Bioresorbable Phosphate Optical Fibres
Journal of Lightwave Technology, 2019Co-Authors: Antreas Theodosiou, Nadia Giovanna Boetti, Edoardo Ceci-ginistrelli, Daniel Milanese, Davide Janner, Diego Pugliese, Kyriacos KalliAbstract:We report on the realization of different types of optical sensors in a bioresorbable phosphate glass optical fiber using a femtosecond laser operating at 517 nm. We inscribed fiber Bragg Grating-based optical filters such as uniform Bragg Gratings, chirped Gratings, and Fabry–Perot cavities, using the plane-by-plane direct write inscription. The Gratings were characterized in reflection and tested as sensors for temperature and relative humidity. We studied the stability and resilience of the Gratings when inserted in high humidity environments (>95%) for 52 h and observed the evolution of the Grating characteristics during this period.
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point by point fiber bragg Grating inscription in free standing step index and photonic crystal fibers using near ir femtosecond laser
Optics Letters, 2010Co-Authors: Thomas Geernaert, Kyriacos Kalli, Francis Berghmans, Tomasz Nasilowski, Jan Wojcik, Waclaw Urbanczyk, Charalambos Koutsides, Michael Komodromos, Hugo ThienpontAbstract:We report what we believe to be the first highly symmetric first-order IR femtosecond laser fiber Bragg Gratings within the telecommunications C band in free-standing optical fiber, fabricated with a relatively low NA lens and without use of oil immersion techniques. This Grating features the smallest dimensions for a point-by-point fiber Grating reported so far (to our knowledge). This achievement paves the way to rapid mass manufacturing of highly efficient and stable Bragg Gratings using ultrafast lasers in any type of fiber. Mastering this femtosecond Grating inscription technique also allowed the fabrication of the first Bragg Gratings with direct near-IR femtosecond inscription in photonic crystal fibers, and without the use of techniques that rely on the compensation of the holey structure.
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annealing and temperature coefficient study of type ia fibre bragg Gratings inscribed under strain and no strain implications to optical fibre component reliability
Reliability of optical fiber components devices systems and networks. Conference, 2006Co-Authors: Kyriacos Kalli, Michael Komodromos, George Simpson, Helen L Dobb, David J Webb, Ian BennionAbstract:The annealing properties of Type IA Bragg Gratings are investigated and compared with Type I and Type IIA Bragg Gratings. The transmission properties (mean and modulated wavelength components) of Gratings held at predetermined temperatures are recorded from which decay characteristics are inferred. Our data show critical results concerning the high temperature stability of Type IA Gratings, as they undergo a drastic initial decay at 100°C, with a consequent mean index change that is severely reduced at this temperature However, the modulated index change of IA Gratings remains stable at lower annealing temperatures of 80°C, and the mean index change decays at a comparable rate to Type I Gratings at 80°C. Extending this work to include the thermal decay of Type IA Gratings inscribed under strain shows that the application of strain quite dramatically transforms the temperature characteristics of the Type IA Grating, modifying the temperature coefficient and annealing curves, with the Grating showing a remarkable improvement in high temperature stability, leading to a robust Grating that can survive temperatures exceeding 180°C. Under conditions of inscription under strain it is found that the temperature coefficient increases, but is maintained at a value considerably different to the Type I Grating. Therefore, the combination of Type I and IA (strained) Gratings make it possible to decouple temperature and strain over larger temperature excursions.
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type 1a fibre bragg Grating photosensitivity and the development of optimum temperature invariant type i type ia strain sensors
Photonics Europe, 2004Co-Authors: George A Simpson, Kyriacos Kalli, Lin Zhang, Kaiming Zhou, Ian BennionAbstract:Type 1A fibre Bragg Gratings (FBG) form only after the erasure of a standard Grating in hydrogenated germanosilicate fibre, under prolonged UV exposure. They are distinct from other Grating types as they exhibit a uniquely large increase in the mean index of the core, readily identifiable by a large red shift in the Bragg wavelength. Type 1A Gratings can surpass the conventional mean index change by a factor of six with a typical red shift of up to 20nm, interpreted as a mean index increase of up to 1.9x10 -2 . Importantly, 1A Gratings have been shown to exhibit the lowest temperature coefficient of all FBG, which makes them ideal for use as temperature compensated, dual Grating sensors. We report on the formation of Type 1A Gratings and the correlation between the mean index change of the Grating and the growth of a loss band at close to 1400nm that is associated with the formation of OH centres within the fibre. We present annealing data comparing the decay of Type 1 and Type 1A Gratings. Finally, we demonstrate a dual temperature compensated strain sensor system, based on two adjoining Type 1 and Type 1A Gratings, which have been formed using a common phase mask, yet with central wavelengths many nm apart.
Ralf K Heilmann - One of the best experts on this subject based on the ideXlab platform.
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manufacture and performance of blazed soft x ray transmission Gratings for arcus and lynx
Optics for EUV X-Ray and Gamma-Ray Astronomy X, 2021Co-Authors: Ralf K Heilmann, Alexander R Bruccoleri, Jungki Song, H L Marshall, Bethany Levenson, Brian Smallshaw, Mallory Whalen, Alan Garner, Sarah N T Heine, Matthew CookAbstract: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
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lynx Grating spectrometer design optimizing chirped transmission Gratings
Space Telescopes and Instrumentation 2020: Ultraviolet to Gamma Ray, 2020Co-Authors: H M Gunther, Ralf K HeilmannAbstract:Lynx is one of four large-mission concept studies for NASA’s 2020 Decadal survey. The design reference mission includes an X-ray Grating spectrometer (XGS) based on critical-angle transmission (CAT) Gratings. In the past we studied different Grating sizes and arrangements using traditional flat CAT Gratings with constant bar spacing. However, new technology development brings chirped Gratings in reach. Using chirped Gratings where the Grating bar spacing varies over a Grating allows us to fill the aperture with larger Gratings because the chirp can compensate for some aberrations caused by the deviation of large flat Gratings from the Rowland torus. This reduces the area blocked by Grating support structures. Using larger Gratings also carries potential cost savings. We use ray-tracing to study an XGS design with chirped Grating and find that using chirped Gratings of 80 ∗ 160 mm size allows us to reduce the number of Gratings from a few thousand to a few hundred, while simultaneously increasing the effective area by 25% and keeping the resolving power constant. Bending those Gratings to maintain a constant blaze angle over the entire Grating increases the effective area by another 5-10%.
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lynx soft x ray critical angle transmission Grating spectrometer
Journal of Astronomical Telescopes Instruments and Systems, 2019Co-Authors: H M Gunther, Ralf K HeilmannAbstract:Lynx is one of four Surveyor-class mission concept studies for the 2020 Astrophysics Decadal Survey. It features an x-ray telescope with an unprecedented collecting area of 2 m2 at 1 keV and a point-spread function of 0.5 arc sec. We describe the status of critical-angle transmission (CAT) Grating technology development and perform ray-traces for a CAT Grating x-ray spectrometer that can reach high spectral resolving power λ / Δλ > 5000 (often exceeding 7500) and effective area around 4000 cm2 in the soft x-ray band (0.2 to 2 keV). To achieve these characteristics, about two-thirds of the aperture must be covered with Gratings. CAT Gratings are mostly transparent at high energies, and thus hard x-rays can still be used for simultaneous imaging spectroscopy using a microcalorimeter array. We simulate several design scenarios and investigate how subaperturing can be most effectively used to increase performance. For large Gratings, the resolving power is limited by the deviation of flat Gratings from the ideal Rowland torus surface. Chirped Gratings, i.e., Gratings where the spacing of Grating bars is variable, can overcome this limitation. Alignment tolerances in many degrees of freedom can be achieved with machining tolerances. We outline the development path to CAT Grating performance improvements and discuss future ray-trace work to refine the design of the spectrometer.
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critical angle transmission Grating technology development for high resolving power soft x ray spectrometers on arcus and lynx
Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series, 2017Co-Authors: Ralf K Heilmann, J A Gaskin, Alexander R Bruccoleri, Jungki Song, Jeffery J Kolodziejczak, Stephen L Odell, Peter Cheimetz, Edward Hertz, Randall K Smith, V BurwitzAbstract:Soft x-ray spectroscopy with high resolving power (R = λ/Δλ) and large effective area (A) addresses numerous unanswered science questions about the physical laws that lead to the structure of our universe. In the soft x-ray band R > 1000 can currently only be achieved with diffraction Grating-based spectroscopy. Criticalangle transmission (CAT) Gratings combine the advantages of blazed reflection Gratings (high efficiency, use of higher diffraction orders) with those of conventional transmission Gratings (relaxed alignment tolerances and temperature requirements, transparent at higher energies, low mass), resulting in minimal mission resource requirements, while greatly improving figures of merit. Diffraction efficiency > 33% and R > 10, 000 have been demonstrated for CAT Gratings. Last year the technology has been certified at Technology Readiness Level 4 based on a probe class mission concept. The Explorer-scale (A > 450 cm2 , R > 2500) Grating spectroscopy Arcus mission can be built with today's CAT Grating technology and has been selected in the current Explorer round for a Phase A concept study. Its figure of merit for the detection of weak absorption lines will be an order of magnitude larger than current instruments on Chandra and XMM-Newton. Further CAT Grating technology development and improvements in the angular resolution of x-ray optics can provide another order of magnitude improvement in performance, as is envisioned for the X-ray Surveyor/Lynx mission concept currently under development for input into the 2020 Decadal Survey. For Arcus we have tested CAT Gratings in a spectrometer setup in combination with silicon pore optics (SPO) and obtained resolving power results that exceed Arcus requirements before and after environmental testing of the Gratings. We have recently fabricated the largest (32 mm x 32 mm) CAT Gratings to date, and plan to increase Grating size further. We mounted two of these large Gratings to frames and aligned them in the roll direction using a laser-based technique. Simultaneous x-ray illumination of both Gratings with an SPO module demonstrated that we can exceed Arcus Grating-to-Grating alignment requirements without x rays.
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critical angle x ray transmission Grating spectrometer with extended bandpass and resolving power 10 000
Proceedings of SPIE, 2016Co-Authors: Ralf K Heilmann, J A Gaskin, Alexander R Bruccoleri, Jeffery J Kolodziejczak, Stephen L Odell, Ritwik Bhatia, Mark L SchattenburgAbstract:A number of high priority subjects in astrophysics can be addressed by a state-of-the-art soft x-ray Grating spectrometer, such as the role of Active Galactic Nuclei in galaxy and star formation, characterization of the Warm-Hot Intergalactic Medium and the missing baryon problem, characterization of halos around the Milky Way and nearby galaxies, as well as stellar coronae and surrounding winds and disks. An Explorer-scale, largearea (> 1,000 cm2), high resolving power (R =λ/Δλ > 3,000) soft x-ray Grating spectrometer is highly feasible based on Critical-Angle Transmission (CAT) Grating technology, even for telescopes with angular resolution of 5-10 arcsec. Still, significantly higher performance can be provided by a CAT Grating spectrometer on an X-ray- Surveyor-type mission. CAT Gratings combine the advantages of blazed reflection Gratings (high efficiency, use of higher diffraction orders) with those of conventional transmission Gratings (lowmass, relaxed alignment tolerances and temperature requirements, transparent at higher energies) with minimalmission resource requirements. They are high-efficiency blazed transmission Gratings that consist of freestanding, ultra-high aspect-ratio Grating bars fabricated from silicon-on-insulator (SOI) wafers using advanced anisotropic dry and wet etch techniques. Blazing is achieved through grazing-incidence reflection off the smooth Grating bar sidewalls. The reflection properties of silicon are well matched to the soft x-ray band, and existing silicon CAT Gratings can exceed 30% absolute diffraction efficiency, with clear paths for further improvement. Nevertheless, CAT Gratings with sidewalls made of higher atomic number elements allow extension of the CAT Grating principle to higher energies and larger dispersion angles, thus enabling higher resolving power at shorter wavelengths. We show x-ray data from CAT Gratings coated with a thin layer of platinum using atomic layer deposition, and demonstrate efficient blazing to higher energies and much larger blaze angles than possible with silicon alone. We also report on measurements of the resolving power of a breadboard CAT Grating spectrometer consisting of a Wolter-I slumped-glass focusing mirror pair from Goddard Space Flight Center and CAT Gratings, performed at the Marshall Space Flight Center Stray Light Facility. Measurement of the Al Kα doublet in 18th diffraction order shows resolving power > 10,000, based on conservative preliminary analysis. This demonstrates that currently fabricated CAT Gratings are compatible with the most advanced Grating spectrometer instrument designs for future soft x-ray spectroscopy missions.
Dan Grobnic - One of the best experts on this subject based on the ideXlab platform.
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low loss type ii regenerative bragg Gratings made with ultrafast radiation
Optics Express, 2016Co-Authors: Dan Grobnic, Cyril Hnatovsky, Stephen J MihailovAbstract:A novel type of fiber Bragg Grating is produced by annealing a type I-like Grating that is written with multiple infrared femtosecond laser pulses through a phase mask under conditions that are typically used to fabricate thermally stable type II Gratings. This new Grating is created through a process similar to a regenerative one and displays low loss and high resilience in a 1000 °C ambient environment. Such Gratings are ideally suited for quasi-distributed sensing at high temperatures.
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bragg Gratings made in highly nonlinear bismuth oxide fibers with ultrafast ir radiation
IEEE Photonics Technology Letters, 2010Co-Authors: Dan Grobnic, Robert B Walker, S J Mihailov, Christopher W Smelser, Ping LuAbstract:High-quality Bragg Gratings with refractive index modulations > 7 × 10-4 were induced in highly nonlinear bismuth oxide glass fibers using ultrafast infrared radiation and a phase mask. Grating reflectivities approaching 95% for a 6-mm-long Grating were achieved. Annealing tests show good thermal stability of the Grating structure below 220°C. The Bragg resonance shift with temperature is observed to be 3-4 times higher than similar Gratings in silica fiber.
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sapphire fiber bragg Grating sensor made using femtosecond laser radiation for ultrahigh temperature applications
IEEE Photonics Technology Letters, 2004Co-Authors: Dan Grobnic, Christopher W Smelser, Stephen J Mihailov, Huimin DingAbstract:We report for the first time the inscription of retro-reflective Bragg Gratings in multimode crystalline sapphire fiber. The Gratings were fabricated using 800-nm femtosecond laser radiation and a phase mask. The Grating behavior was investigated up to 1500/spl deg/C with no detectable reduction in the Grating reflectivity or hysteresis in the Bragg resonance. Measurements of the change in the effective index of the fiber as a function of temperature are reported and the performance of the Grating as a temperature sensor is evaluated.
Ian Bennion - One of the best experts on this subject based on the ideXlab platform.
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annealing and temperature coefficient study of type ia fibre bragg Gratings inscribed under strain and no strain implications to optical fibre component reliability
Reliability of optical fiber components devices systems and networks. Conference, 2006Co-Authors: Kyriacos Kalli, Michael Komodromos, George Simpson, Helen L Dobb, David J Webb, Ian BennionAbstract:The annealing properties of Type IA Bragg Gratings are investigated and compared with Type I and Type IIA Bragg Gratings. The transmission properties (mean and modulated wavelength components) of Gratings held at predetermined temperatures are recorded from which decay characteristics are inferred. Our data show critical results concerning the high temperature stability of Type IA Gratings, as they undergo a drastic initial decay at 100°C, with a consequent mean index change that is severely reduced at this temperature However, the modulated index change of IA Gratings remains stable at lower annealing temperatures of 80°C, and the mean index change decays at a comparable rate to Type I Gratings at 80°C. Extending this work to include the thermal decay of Type IA Gratings inscribed under strain shows that the application of strain quite dramatically transforms the temperature characteristics of the Type IA Grating, modifying the temperature coefficient and annealing curves, with the Grating showing a remarkable improvement in high temperature stability, leading to a robust Grating that can survive temperatures exceeding 180°C. Under conditions of inscription under strain it is found that the temperature coefficient increases, but is maintained at a value considerably different to the Type I Grating. Therefore, the combination of Type I and IA (strained) Gratings make it possible to decouple temperature and strain over larger temperature excursions.
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type 1a fibre bragg Grating photosensitivity and the development of optimum temperature invariant type i type ia strain sensors
Photonics Europe, 2004Co-Authors: George A Simpson, Kyriacos Kalli, Lin Zhang, Kaiming Zhou, Ian BennionAbstract:Type 1A fibre Bragg Gratings (FBG) form only after the erasure of a standard Grating in hydrogenated germanosilicate fibre, under prolonged UV exposure. They are distinct from other Grating types as they exhibit a uniquely large increase in the mean index of the core, readily identifiable by a large red shift in the Bragg wavelength. Type 1A Gratings can surpass the conventional mean index change by a factor of six with a typical red shift of up to 20nm, interpreted as a mean index increase of up to 1.9x10 -2 . Importantly, 1A Gratings have been shown to exhibit the lowest temperature coefficient of all FBG, which makes them ideal for use as temperature compensated, dual Grating sensors. We report on the formation of Type 1A Gratings and the correlation between the mean index change of the Grating and the growth of a loss band at close to 1400nm that is associated with the formation of OH centres within the fibre. We present annealing data comparing the decay of Type 1 and Type 1A Gratings. Finally, we demonstrate a dual temperature compensated strain sensor system, based on two adjoining Type 1 and Type 1A Gratings, which have been formed using a common phase mask, yet with central wavelengths many nm apart.
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the interrogation and multiplexing of long period Grating curvature sensors using a bragg Grating based derivative spectroscopy technique
Measurement Science and Technology, 2004Co-Authors: Thomas D P Allsop, David J Webb, Tim Earthrowl, R Reeves, Ian BennionAbstract:A long period Grating is interrogated with a fibre Bragg Grating using a derivative spectroscopy technique. A quasi-linear relationship between the output of the sensing scheme and the curvature experienced by the long period Grating is demonstrated, with a sensitivity of 5.05 m and with an average curvature resolution of 2.9 × 10-2 m-1. In addition, the feasibility of multiplexing an in-line series of long period Gratings with this interrogation scheme is demonstrated with two pairs of fibre Bragg Gratings and long period Gratings. With this arrangement the cross-talk error between channels was less than ± 2.4 × 10-3 m-1.
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dependence of temperature and strain coefficients on fiber Grating type and its application to simultaneous temperature and strain measurement
Optics Letters, 2002Co-Authors: Xuewen Shu, Y Liu, Donghui Zhao, B A L Gwandu, F Floreani, Lin Zhang, Ian BennionAbstract:We report an investigation of the dependence of the temperature and strain coefficients on the Grating type for fiber Bragg Gratings that are UV inscribed in B/Ge-codoped fiber with and without hydrogenation. The results reveal that all types of Grating exhibit similar strain sensitivities but markedly different temperature sensitivities, greater for Gratings inscribed in hydrogen-free rather than hydrogenated fiber and substantially less in type IA Gratings than all others. The sensitivity characteristics of these Gratings have been used to implement a new type of dual-Grating sensor for simultaneous measurement of temperature and strain that has properties superior to those of previously reported structures.
Mark L Schattenburg - One of the best experts on this subject based on the ideXlab platform.
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critical angle x ray transmission Grating spectrometer with extended bandpass and resolving power 10 000
Proceedings of SPIE, 2016Co-Authors: Ralf K Heilmann, J A Gaskin, Alexander R Bruccoleri, Jeffery J Kolodziejczak, Stephen L Odell, Ritwik Bhatia, Mark L SchattenburgAbstract:A number of high priority subjects in astrophysics can be addressed by a state-of-the-art soft x-ray Grating spectrometer, such as the role of Active Galactic Nuclei in galaxy and star formation, characterization of the Warm-Hot Intergalactic Medium and the missing baryon problem, characterization of halos around the Milky Way and nearby galaxies, as well as stellar coronae and surrounding winds and disks. An Explorer-scale, largearea (> 1,000 cm2), high resolving power (R =λ/Δλ > 3,000) soft x-ray Grating spectrometer is highly feasible based on Critical-Angle Transmission (CAT) Grating technology, even for telescopes with angular resolution of 5-10 arcsec. Still, significantly higher performance can be provided by a CAT Grating spectrometer on an X-ray- Surveyor-type mission. CAT Gratings combine the advantages of blazed reflection Gratings (high efficiency, use of higher diffraction orders) with those of conventional transmission Gratings (lowmass, relaxed alignment tolerances and temperature requirements, transparent at higher energies) with minimalmission resource requirements. They are high-efficiency blazed transmission Gratings that consist of freestanding, ultra-high aspect-ratio Grating bars fabricated from silicon-on-insulator (SOI) wafers using advanced anisotropic dry and wet etch techniques. Blazing is achieved through grazing-incidence reflection off the smooth Grating bar sidewalls. The reflection properties of silicon are well matched to the soft x-ray band, and existing silicon CAT Gratings can exceed 30% absolute diffraction efficiency, with clear paths for further improvement. Nevertheless, CAT Gratings with sidewalls made of higher atomic number elements allow extension of the CAT Grating principle to higher energies and larger dispersion angles, thus enabling higher resolving power at shorter wavelengths. We show x-ray data from CAT Gratings coated with a thin layer of platinum using atomic layer deposition, and demonstrate efficient blazing to higher energies and much larger blaze angles than possible with silicon alone. We also report on measurements of the resolving power of a breadboard CAT Grating spectrometer consisting of a Wolter-I slumped-glass focusing mirror pair from Goddard Space Flight Center and CAT Gratings, performed at the Marshall Space Flight Center Stray Light Facility. Measurement of the Al Kα doublet in 18th diffraction order shows resolving power > 10,000, based on conservative preliminary analysis. This demonstrates that currently fabricated CAT Gratings are compatible with the most advanced Grating spectrometer instrument designs for future soft x-ray spectroscopy missions.
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critical angle x ray transmission Grating spectrometer with extended bandpass and resolving power 10 000
arXiv: Instrumentation and Methods for Astrophysics, 2016Co-Authors: Ralf K Heilmann, J A Gaskin, Alexander R Bruccoleri, Jeffery J Kolodziejczak, Stephen L Odell, Ritwik Bhatia, Mark L SchattenburgAbstract:Several high priority subjects in astrophysics can be addressed by a state-of-the-art soft x-ray Grating spectrometer (XGS). An Explorer-scale, large-area (> 1,000 cm2), high resolving power (R > 3,000) XGS is highly feasible based on Critical-Angle Transmission (CAT) Gratings, even for telescopes with angular resolution of 5-10 arcsec. Significantly higher performance can be provided by a CAT XGS on an X-ray-Surveyor-type mission. CAT Gratings combine the advantages of blazed reflection Gratings (high efficiency, use of higher diffraction orders) with those of transmission Gratings (low mass, relaxed alignment and temperature requirements, transparent at high energies) with minimal mission resource demands. They are high-efficiency blazed transmission Gratings that consist of freestanding, ultra-high aspect-ratio Grating bars made from SOI wafers using anisotropic dry and wet etch techniques. Blazing is achieved through reflection off Grating bar sidewalls. Silicon is well matched to the soft x-ray band, and existing silicon CAT Gratings exceed 30% absolute diffraction efficiency, with clear paths for improvement. CAT Gratings coated with heavier elements allow extension of the CAT Grating principle to higher energies and larger angles, enabling higher resolving power at shorter wavelengths. We show x-ray data from CAT Gratings coated with platinum using atomic layer deposition, and demonstrate blazing to higher energies and much larger blaze angles than possible with silicon. We measure resolving power of a CAT XGS consisting of a Wolter-I focusing mirror pair from GSFC and CAT Gratings, performed at the MSFC SLF. Measurement of the Al Ka doublet in 18th order shows resolving power > 10,000, based on preliminary analysis. This demonstrates that currently fabricated CAT Gratings are compatible with the most advanced XGS designs for future soft x-ray spectroscopy missions.
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fabrication update on critical angle transmission Gratings for soft x ray Grating spectrometers
Proceedings of SPIE, 2011Co-Authors: Ralf K Heilmann, Alexander R Bruccoleri, Pran Mukherjee, Jonathan Yam, Mark L SchattenburgAbstract:Diffraction Grating-based, wavelength dispersive high-resolution soft x-ray spectroscopy of celestial sources promises to reveal crucial data for the study of the Warm-Hot Intergalactic Medium, the Interstellar Medium, warm absorption and outflows in Active Galactic Nuclei, coronal emission from stars, and other areas of interest to the astrophysics community. Our recently developed critical-angle transmission (CAT) Gratings combine the advantages of the Chandra high and medium energy transmission Gratings (low mass, high tolerance of misalignments and figure errors, polarization insensitivity) with those of blazed reflection Gratings (high broad band diffraction efficiency, high resolution through use of higher diffraction orders) such as the ones on XMM-Newton. Extensive instrument and system configuration studies have shown that a CAT Grating-based spectrometer is an outstanding instrument capable of delivering resolving power on the order of 5,000 and high effective area, even with a telescope point-spread function on the order of many arc-seconds. We have fabricated freestanding, ultra-high aspect-ratio CAT Grating bars from silicon-on-insulator wafers using both wet and dry etch processes. The 200 nm-period Grating bars are supported by an integrated Level 1 support mesh, and a coarser external Level 2 support mesh. The resulting Grating membrane is mounted to a frame, resulting in a Grating facet. Many such facets comprise a Grating array that provides light-weight coverage of large-area telescope apertures. Here we present fabrication results on the integration of CAT Gratings and the different high-throughput support mesh levels and on membrane-frame bonding. We also summarize recent x-ray data analysis of 3 and 6 micron deep wet-etched CAT Grating prototypes.
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diffraction efficiency of 200 nm period critical angle transmission Gratings in the soft x ray and extreme ultraviolet wavelength bands
Applied Optics, 2011Co-Authors: Ralf K Heilmann, Alexander R Bruccoleri, Minseung Ahn, Chihhao Chang, Eric M Gullikson, Pran Mukherjee, Mark L SchattenburgAbstract:We report on measurements of the diffraction efficiency of 200-nm-period freestanding blazed transmission Gratings for wavelengths in the 0.96 to 19.4 nm range. These critical-angle transmission (CAT) Gratings achieve highly efficient blazing over a broad band via total external reflection off the sidewalls of smooth, tens of nanometer thin ultrahigh aspect-ratio silicon Grating bars and thus combine the advantages of blazed x-ray reflection Gratings with those of more conventional x-ray transmission Gratings. Prototype Gratings with maximum depths of 3.2 and 6 μm were investigated at two different blaze angles. In these initial CAT Gratings the Grating bars are monolithically connected to a cross support mesh that only leaves less than half of the Grating area unobstructed. Because of our initial fabrication approach, the support mesh bars feature a strongly trapezoidal cross section that leads to varying CAT Grating depths and partial absorption of diffracted orders. While theory predicts broadband absolute diffraction efficiencies as high as 60% for ideal CAT Gratings without a support mesh, experimental results show efficiencies in the range of ∼50–100% of theoretical predictions when taking the effects of the support mesh into account. Future minimization of the support mesh therefore promises broadband CAT Grating absolute diffraction efficiencies of 50% or higher.
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fabrication and performance of blazed transmission Gratings for x ray astronomy
Proceedings of SPIE, 2008Co-Authors: Ralf K Heilmann, Minseung Ahn, Mark L SchattenburgAbstract:We have developed a new type of soft x-ray diffraction Grating. This critical-angle transmission (CAT) Grating combines the advantages of traditional transmission Gratings (low mass, extremely relaxed alignment and flatness tolerances) with those of x-ray reflection Gratings (high efficiency due to blazing in the direction of grazing-incidence reflection, increased resolution due to the use of higher diffraction orders). In addition, Grating spectrometers based on CAT Gratings are well-suited for co-existence with high-energy focal plane microcalorimeter detectors as planned for the Constellation-X mission, since most high-energy x rays are neither absorbed nor deflected, and arrive at the telescope focus. We describe the CAT Grating principle and design, and fabrication and x-ray diffraction efficiency results for a CAT Grating with 1742 lines/mm. We have observed up to 46% diffraction efficiency in a single order, and up to 55% at blaze at extreme ultraviolet wavelengths. We present our recent fabrication and soft x-ray diffraction results for 200 nm-period (5000 lines/mm) Gratings.
