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Keywords = astrophotonics

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12 pages, 841 KB  
Review
Post-AGB Stars as Tracers of AGB Nucleosynthesis: An Update
by Devika Kamath and Hans Van Winckel
Universe 2022, 8(4), 233; https://doi.org/10.3390/universe8040233 - 11 Apr 2022
Cited by 9 | Viewed by 3780
Abstract
The chemical evolution of galaxies is governed by the chemical yields from stars, and here we focus on the important contributions from asymptotic giant branch (AGB) stars. AGB nucleosynthesis is, however, still riddled with complexities. Observations from post-asymptotic giant branch (post-AGB) stars serve [...] Read more.
The chemical evolution of galaxies is governed by the chemical yields from stars, and here we focus on the important contributions from asymptotic giant branch (AGB) stars. AGB nucleosynthesis is, however, still riddled with complexities. Observations from post-asymptotic giant branch (post-AGB) stars serve as exquisite tools to quantify and understand AGB nucleosynthesis. In this contribution, we review the invaluable constraints provided by post-AGB stars with which to study AGB nucleosynthesis, especially the slow neutron capture nucleosynthesis (i.e., the s-process). Full article
(This article belongs to the Special Issue AGB Stars—In Honor of Professor Maurizio Busso on the Occasion of His 70th Birthday)
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12 pages, 17615 KB  
Article
Laser 3D Printing of Inorganic Free-Form Micro-Optics
by Diana Gonzalez-Hernandez, Simonas Varapnickas, Greta Merkininkaitė, Arūnas Čiburys, Darius Gailevičius, Simas Šakirzanovas, Saulius Juodkazis and Mangirdas Malinauskas
Photonics 2021, 8(12), 577; https://doi.org/10.3390/photonics8120577 - 14 Dec 2021
Cited by 66 | Viewed by 8287
Abstract
A pilot study on laser 3D printing of inorganic free-form micro-optics is experimentally validated. Ultrafast laser direct-write (LDW) nanolithography is employed for structuring hybrid organic-inorganic material SZ2080TM followed by high-temperature calcination post-processing. The combination allows the production of 3D architectures and the [...] Read more.
A pilot study on laser 3D printing of inorganic free-form micro-optics is experimentally validated. Ultrafast laser direct-write (LDW) nanolithography is employed for structuring hybrid organic-inorganic material SZ2080TM followed by high-temperature calcination post-processing. The combination allows the production of 3D architectures and the heat-treatment results in converting the material to inorganic substances. The produced miniature optical elements are characterized and their optical performance is demonstrated. Finally, the concept is validated for manufacturing compound optical components such as stacked lenses. This is an opening for new directions and applications of laser-made micro-optics under harsh conditions such as high intensity radiation, temperature, acidic environment, pressure variations, which include open space, astrophotonics, and remote sensing. Full article
(This article belongs to the Special Issue Ultrafast Laser Written Photonic, Sensing and Microfluidic Circuits in Transparent Materials)
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11 pages, 582 KB  
Review
The Missing Lead: Developments in the Lead (Pb) Discrepancy in Intrinsically s-Process Enriched Single Post-AGB Stars
by Devika Kamath and Hans Van Winckel
Universe 2021, 7(11), 446; https://doi.org/10.3390/universe7110446 - 19 Nov 2021
Cited by 3 | Viewed by 2271
Abstract
Lead (Pb) is predicted to have large over-abundances with respect to other s-process elements in Asymptotic Giant Branch (AGB) stars, especially of low metallicities. However, our previous abundance studies of s-process enriched post-Asymptotic Giant Branch (post-AGB) stars in the Galaxy and [...] Read more.
Lead (Pb) is predicted to have large over-abundances with respect to other s-process elements in Asymptotic Giant Branch (AGB) stars, especially of low metallicities. However, our previous abundance studies of s-process enriched post-Asymptotic Giant Branch (post-AGB) stars in the Galaxy and the Magellanic Clouds show a discrepancy between observed and predicted Pb abundances. For the subset of post-AGB stars with low metallicities the determined upper limits based on detailed chemical abundance studies are much lower than what is predicted. Recent theoretical studies have pointed to the occurrence of the i-process to explain the observed chemical patterns, especially of Pb. A major development, in the observational context, is the release of the GAIA EDR3 parallaxes of the post-AGBs in the Galaxy, which has opened the gateway to systematically studying the sample of stars as a function of current luminosities (which can be linked to their initial masses). In this paper, we succinctly review the Pb discrepancy in post-AGB stars and present the latest observational and theoretical developments in this research landscape. Full article
(This article belongs to the Special Issue AGB Stars: Element Forges of the Universe)
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39 pages, 4082 KB  
Review
Stellar Chromospheric Variability
by Richard de Grijs and Devika Kamath
Universe 2021, 7(11), 440; https://doi.org/10.3390/universe7110440 - 15 Nov 2021
Cited by 19 | Viewed by 8944
Abstract
Cool stars with convective envelopes of spectral types F and later tend to exhibit magnetic activity throughout their atmospheres. The presence of strong and variable magnetic fields is evidenced by photospheric starspots, chromospheric plages and coronal flares, as well as by strong Ca [...] Read more.
Cool stars with convective envelopes of spectral types F and later tend to exhibit magnetic activity throughout their atmospheres. The presence of strong and variable magnetic fields is evidenced by photospheric starspots, chromospheric plages and coronal flares, as well as by strong Ca ii H+K and Hα emission, combined with the presence of ultraviolet resonance lines. We review the drivers of stellar chromospheric activity and the resulting physical parameters implied by the observational diagnostics. At a basic level, we explore the importance of stellar dynamos and their activity cycles for a range of stellar types across the Hertzsprung–Russell diagram. We focus, in particular, on recent developments pertaining to stellar rotation properties, including the putative Vaughan–Preston gap. We also pay specific attention to magnetic variability associated with close binary systems, including RS Canum Venaticorum, BY Draconis, W Ursae Majoris and Algol binaries. At the present time, large-scale photometric and spectroscopic surveys are becoming generally available, thus leading to a resurgence of research into chromospheric activity. This opens up promising prospects to gain a much improved understanding of chromospheric physics and its wide-ranging impact. Full article
(This article belongs to the Special Issue Stellar Astrophysics)
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18 pages, 1069 KB  
Review
Astrophotonic Spectrographs
by Pradip Gatkine, Sylvain Veilleux and Mario Dagenais
Appl. Sci. 2019, 9(2), 290; https://doi.org/10.3390/app9020290 - 15 Jan 2019
Cited by 57 | Viewed by 7265
Abstract
Astrophotonics is the application of photonic technologies to channel, manipulate, and disperse light from one or more telescopes to achieve scientific objectives in astronomy in an efficient and cost-effective way. Utilizing photonic advantage for astronomical spectroscopy is a promising approach to miniaturizing the [...] Read more.
Astrophotonics is the application of photonic technologies to channel, manipulate, and disperse light from one or more telescopes to achieve scientific objectives in astronomy in an efficient and cost-effective way. Utilizing photonic advantage for astronomical spectroscopy is a promising approach to miniaturizing the next generation of spectrometers for large telescopes. It can be primarily attained by leveraging the two-dimensional nature of photonic structures on a chip or a set of fibers, thus reducing the size of spectroscopic instrumentation to a few centimeters and the weight to a few hundred grams. A wide variety of astrophotonic spectrometers is currently being developed, including arrayed waveguide gratings (AWGs), photonic echelle gratings (PEGs), and Fourier-transform spectrometer (FTS). These astrophotonic devices are flexible, cheaper to mass produce, easier to control, and much less susceptible to vibrations and flexure than conventional astronomical spectrographs. The applications of these spectrographs range from astronomy to biomedical analysis. This paper provides a brief review of this new class of astronomical spectrographs. Full article
(This article belongs to the Special Issue Silicon Photonics – Emerging Devices and Applications)
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13 pages, 2680 KB  
Article
High-Resolution Arrayed-Waveguide-Gratings in Astronomy: Design and Fabrication Challenges
by Andreas Stoll, Ziyang Zhang, Roger Haynes and Martin Roth
Photonics 2017, 4(2), 30; https://doi.org/10.3390/photonics4020030 - 10 Apr 2017
Cited by 34 | Viewed by 11667
Abstract
A comprehensive design of a folded-architecture arrayed-waveguide-grating (AWG)-device, targeted at applications as integrated photonic spectrographs (IPS) in near-infrared astronomy, is presented. The AWG structure is designed for the astronomical H-band (1500 nm–1800 nm) with a theoretical maximum resolving power R = 60,000 at [...] Read more.
A comprehensive design of a folded-architecture arrayed-waveguide-grating (AWG)-device, targeted at applications as integrated photonic spectrographs (IPS) in near-infrared astronomy, is presented. The AWG structure is designed for the astronomical H-band (1500 nm–1800 nm) with a theoretical maximum resolving power R = 60,000 at 1630 nm. The geometry of the device is optimized for a compact structure with a footprint of 5.5 cm × 3.93 cm on SiO 2 platform. To evaluate the fabrication challenges of such high-resolution AWGs, effects of random perturbations of the effective refractive index (RI) distribution in the free propagation region (FPR), as well as small variations of the array waveguide optical lengths are numerically investigated. The results of the investigation show a dramatic degradation of the point spread function (PSF) for a random effective RI distribution with variance values above ∼ 10 - 4 for both the FPR and the waveguide array. Based on the results, requirements on the fabrication technology for high-resolution AWG-based spectrographs are given in the end. Full article
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18 pages, 10651 KB  
Article
Optically Clear and Resilient Free-Form µ-Optics 3D-Printed via Ultrafast Laser Lithography
by Linas Jonušauskas, Darius Gailevičius, Lina Mikoliūnaitė, Danas Sakalauskas, Simas Šakirzanovas, Saulius Juodkazis and Mangirdas Malinauskas
Materials 2017, 10(1), 12; https://doi.org/10.3390/ma10010012 - 2 Jan 2017
Cited by 126 | Viewed by 18349
Abstract
We introduce optically clear and resilient free-form micro-optical components of pure (non-photosensitized) organic-inorganic SZ2080 material made by femtosecond 3D laser lithography (3DLL). This is advantageous for rapid printing of 3D micro-/nano-optics, including their integration directly onto optical fibers. A systematic study of the [...] Read more.
We introduce optically clear and resilient free-form micro-optical components of pure (non-photosensitized) organic-inorganic SZ2080 material made by femtosecond 3D laser lithography (3DLL). This is advantageous for rapid printing of 3D micro-/nano-optics, including their integration directly onto optical fibers. A systematic study of the fabrication peculiarities and quality of resultant structures is performed. Comparison of microlens resiliency to continuous wave (CW) and femtosecond pulsed exposure is determined. Experimental results prove that pure SZ2080 is ∼20 fold more resistant to high irradiance as compared with standard lithographic material (SU8) and can sustain up to 1.91 GW/cm2 intensity. 3DLL is a promising manufacturing approach for high-intensity micro-optics for emerging fields in astro-photonics and atto-second pulse generation. Additionally, pyrolysis is employed to homogeneously shrink structures up to 40% by removing organic SZ2080 constituents. This opens a promising route towards downscaling photonic lattices and the creation of mechanically robust glass-ceramic microstructures. Full article
(This article belongs to the Special Issue Ultrafast Laser-Based Manufacturing)
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