UV Wavelength Range Research Articles

The Driving of Hot Star Winds

AbstractIn the regime of hot stars, winds were not seen as a common thing until the era of UV astronomy. Since we have access to the UV wavelength range, it has become clear that winds are not an exotic phenomenon limited to some special objects, but actually ubiquitous among hot and massive stars. The opacities due to spectral lines are the decisive ingredient that allows hot, massive stars to launch powerful winds. While the fundamental principles of these so-called line-driven winds have been realized decades ago, their proper quantitative prediction is still a major challenge today. Established theoretical and empirical descriptions have allowed us to make major progress on all astrophysical scales. However, we are now reaching their limitations as we still lack various fundamental insights on the nature of hot star winds, thereby hampering us from drawing deeper conclusions, not least when dealing with stellar or sub-stellar companions. This has spawned a new generation of researchers searching for answers with a yet unprecedented level of detail in observational and new theoretical approaches.In these proceedings, the fundamental principles of driving hot star winds will be briefly reviewed. Starting from the classical CAK theory and its extensions, over Monte Carlo and recent comoving-frame-based simulations, the different methods to describe and model the acceleration of hot star winds will be introduced. The review continues with briefly discussing instabilities as well as qualitative and quantitative insights for OB- and Wolf-Rayet-star winds. Moreover, the challenges of companions and their impact on radiation-driven winds are outlined.

Aluminium-Based Plasmonic Sensors in Ultraviolet.

We theoretically investigate the surface plasmon polaritons (SPPs) generated on an Al film covered by an Al2O3 layer in the context of their application as refractive index sensors. The calculated reflection spectra indicate SPP resonance excited by ultraviolet light, which was affected by the thickness of both the metal and the oxide layers on the surface. With optimized geometry, the system can work as a tunable sensor with a wide UV wavelength range 150–300 nm. We report a quality factor of up to 10 and a figure of merit on the order of 9, and these are comparable to the performance of more complicated UV plasmonic nanostructures and allow for the detection of a change of the refraction index. The sensor can operate on the basis of either the incidence angle or wavelength changes. The effect of oxide surface roughness is also investigated with an emphasis on amplitude-based refraction index sensing.

New in situ aerosol hyperspectral optical measurements over 300–700 nm – Part 2: Extinction, total absorption, water- and methanol-soluble absorption observed during the KORUS-OC cruise

Abstract. This two-part study explores hyperspectral (300–700 nm) aerosol optical measurements obtained from in situ sampling methods employed during the May–June 2016 Korea–United States Ocean Color (KORUS-OC) cruise conducted in concert with the broader air quality campaign (KORUS-AQ). Part 1 focused on the hyperspectral measurement of extinction coefficients (σext) using the recently developed in situ Spectral Aerosol Extinction (SpEx) instrument and showed that second-order polynomials provided a better fit to the measured spectra than power law fits. Two dimensional mapping of the second-order polynomial coefficients (a1, a2) was used to explore the information content of the spectra. Part 2 expands on that work by applying a similar analytical approach to filter-based measurements of aerosol hyperspectral total absorption (σabs) and soluble absorption from filters extracted with either deionized water (σDI-abs) or methanol (σMeOH-abs). As was found for σext, second-order polynomials provided a better fit to all three absorption spectra sets. Averaging the measured σext from Part 1 over the filter sampling intervals in this work, hyperspectral single-scattering albedo (ω) was calculated. Water-soluble aerosol composition from the DI extracts was used to examine relationships with the various measured optical properties. In particular, both σDI-abs(365 nm) and σMeOH-abs(365 nm) were found to be best correlated with oxalate (C2O42-), but elevated soluble absorption was found from two chemically and optically distinct populations of aerosols. The more photochemically aged aerosols of those two groups exhibited partial spectra (i.e., the longer wavelengths of the spectral range were below detection) while the less-aged aerosol of the other group exhibited complete spectra across the wavelength range. The chromophores of these groups may have derived from different sources and/or atmospheric processes, such that photochemical age may have been only one factor contributing to the differences in the observed spectra. The differences in the spectral properties of these groups was evident in (a1, a2) maps. The results of the two-dimensional mapping shown in Parts 1 and 2 suggest that this spectral characterization may offer new methods to relate in situ aerosol optical properties to their chemical and microphysical characteristics. However, a key finding of this work is that mathematical functions (whether power laws or second-order polynomials) extrapolated from a few wavelengths or a subrange of wavelengths fail to reproduce the measured spectra over the full 300–700 nm wavelength range. Further, the σabs and ω spectra exhibited distinctive spectral features across the UV and visible wavelength range that simple functions and extrapolations cannot reproduce. These results show that in situ hyperspectral measurements provide valuable new data that can be probed for additional information relating in situ aerosol optical properties to the underlying physicochemical properties of ambient aerosols. It is anticipated that future studies examining in situ aerosol hyperspectral properties will not only improve our ability to use optical data to characterize aerosol physicochemical properties, but that such in situ tools will be needed to validate hyperspectral remote sensors planned for space-based observing platforms.

Masked Alkyne Equivalents for the Synthesis of Mechanically Interlocked Polyynes**

AbstractPolyyne polyrotaxanes, encapsulated cyclocarbon catenanes and other fascinating mechanically interlocked carbon‐rich architectures should become accessible if masked alkyne equivalents (MAEs) can be developed that are large enough to prevent unthreading of a macrocycle, and that can be cleanly unmasked under mild conditions. Herein, we report the synthesis of a new bulky MAE based on t‐butylbicyclo[4.3.1]decatriene. This MAE was used to synthesize a polyyne [2]rotaxane and a masked‐polyyne [3]rotaxane by Cadiot–Chodkiewicz coupling. Glaser cyclo‐oligomerization of the [2]rotaxane gave masked cyclocarbon catenanes. The unmasking behavior of the catenanes and rotaxanes was tested by photolysis at a range of UV wavelengths. Photochemical unmasking did not proceed cleanly enough to prepare extended encapsulated polyyne polyrotaxanes. We highlight the scope and challenges involved with this approach to interlocked carbon‐rich architectures.

Masked Alkyne Equivalents for the Synthesis of Mechanically Interlocked Polyynes*.

Polyyne polyrotaxanes, encapsulated cyclocarbon catenanes and other fascinating mechanically interlocked carbon-rich architectures should become accessible if masked alkyne equivalents (MAEs) can be developed that are large enough to prevent unthreading of a macrocycle, and that can be cleanly unmasked under mild conditions. Herein, we report the synthesis of a new bulky MAE based on t-butylbicyclo[4.3.1]decatriene. This MAE was used to synthesize a polyyne [2]rotaxane and a masked-polyyne [3]rotaxane by Cadiot-Chodkiewicz coupling. Glaser cyclo-oligomerization of the [2]rotaxane gave masked cyclocarbon catenanes. The unmasking behavior of the catenanes and rotaxanes was tested by photolysis at a range of UV wavelengths. Photochemical unmasking did not proceed cleanly enough to prepare extended encapsulated polyyne polyrotaxanes. We highlight the scope and challenges involved with this approach to interlocked carbon-rich architectures.

Determination of As, Hg, S, and Se in liquid jets by laser-based optical diagnostic technique

Laser-induced breakdown spectroscopy (LIBS) has been evaluated for measurement of As, Hg, S, and Se in aqueous samples. Single pulse (SP) and double pulse (DP) LIBS, with a 1064 nm Nd: YAG laser source, were utilized to generate micro plasma from the surface of a liquid jet containing these elements. Plasma emission was collected at a 45° angle with the laser beam for As and Se detection in UV wavelength range. However, the confocal mode was used to collect the atomic emission for Hg and S detection in visible and near IR range, respectively. Atomic emission lines 228.81 nm for As, 546.07 nm for Hg, 921.2 nm for S, and 196.09, 203.98 and 206.32 nm for Se were detected in the LIBS spectra. Calibration curves were developed to estimate the limit of detection for each analyte and found to be 2, 16, 16, and 29 ppm for As, Hg, S, and Se, respectively, with SP LIBS and 0.4, 8, 8 and 11 ppm, respectively, with DP LIBS. The study has implications in monitoring of these pollutants in flue gas desulfurization (FGD) wastewater.

Visible-Light-Driven Methane Conversion with Oxygen Enabled by Atomically Precise Nickel Catalyst

It remains an extreme challenge to activate thermodynamically unfavorable, chemically inert methane molecules under mild conditions. Herein, we report a molecular-like nickel-thiolate hexameric clu...

Characterisation of Au surface properties relevant for UV photoemission-based charge control for space inertial sensors

Precision space inertial sensors used for satellite geodesy missions, tests of fundamental physics, and gravitational wave observation utilise UV photoemission to control the electric potential of free-falling test masses with respect to their surrounding electrode housings. Successful generation of photoelectrons requires UV light energies greater than the work function of the illuminated surface. To ensure bi-polar test mass charge control (positive and negative charge rates), the quantum yields of the test mass and electrode housing surfaces must be well-balanced. LISA Pathfinder used mercury vapour lamps at 254 nm to discharge the gold coated test mass by likely relying on contaminants to lower the work function of gold from its nominal value of 5.2 eV. The LISA gravitational wave mission plans to use UV light emitting diodes (LEDs) instead of mercury vapour lamps. These UV LEDs have a lower mass, higher power efficiency, and produce light at wavelengths below 240 nm. In this paper, we measure the quantum yields of several Au-coated surfaces over a range of UV wavelengths and environmental conditions, varying temperature, vacuum pressure, and measuring over long periods of time. We use these data to draw conclusions and make recommendations for the development and handling of precision space inertial sensors for LISA and for other missions in the future.

Intra- and inter-conduction band optical absorption processes in β -Ga2O3

β-Ga2O3 is an ultra-wide bandgap semiconductor and is thus expected to be optically transparent to light of sub-bandgap wavelengths well into the ultraviolet. Contrary to this expectation, it is found here that free electrons in n-doped β-Ga2O3 absorb light from the IR to the UV wavelength range via intra- and inter-conduction band optical transitions. Intra-conduction band absorption occurs via an indirect optical phonon mediated process with 1/ω3 dependence in the visible to near-IR wavelength range. This frequency dependence markedly differs from the 1/ω2 dependence predicted by the Drude model of free-carrier absorption. The inter-conduction band absorption between the lowest conduction band and a higher conduction band occurs via a direct optical process at λ∼349 nm (3.55 eV). Steady state and ultrafast optical spectroscopy measurements unambiguously identify both these absorption processes and enable quantitative measurements of the inter-conduction band energy and the frequency dependence of absorption. Whereas the intra-conduction band absorption does not depend on light polarization, inter-conduction band absorption is found to be strongly polarization dependent. The experimental observations, in excellent agreement with recent theoretical predictions for β-Ga2O3, provide important limits of sub-bandgap transparency for optoelectronics in the deep-UV to visible wavelength range and are also of importance for high electric field transport effects in this emerging semiconductor.

A novel bis(terpyridine) with π−conjugated phenyl viologen and its metallo- supramolecular polymers: Synthesis and electrochromism

A novel phenylene viologen functionalized bis(terpyridine) is synthesized and characterized with 1HNMR and Maldi-tof-MS. This rod-like and π-conjugated molecule, 1,1'-[4'-(4-phenyl)-2,2:6′,2″- terpyridine-4,4′-bipyridine-1,1′-diium dichloride (TPV+22Cl−), synthesized by Zincke reaction of 4'-(4-aminophenyl)-2,2:6′,2″-terpyridine with 1,1′-bis (2,4-dinitrophenyl)-4,4′-bipyridine,1,1′-diium dichloride, exhibited strong absorption and fluorescence in wide UV and visible wavelength range. It complexes with Fe- and Ru- ions and can self-assemble into metallo-supramolecular polymers in solution, which can be coated on ITO-glass. The electrochemical characteristics of TPV+22Cl− and its Fe-TPV+2-BF4 supramolecular polymer in solution were studied with cyclic voltammetry. Four different color states, colorless (transparent), purple, reddish brown and grayish green, were observed in a cycle of redox reaction during the cyclic voltammetry scanning. A simple liquid electrochromic device with the Fe-TPV+2-BF4 supramolecular polymer film as working electrode, and with LiClO4 aqueous and K3Fe(CN)6, was fabricated. It can be colored/bleached reversibly between purple and green-yellowish colors by switching the applied voltage from 0 to 0.8 V. The π-conjugation among the bis(terpyridine)s and the phenylene viologen leads the subunits electronically and chemically connected. This interesting viologen functionalized bis(terpyridine) dye will find applications in wide ranges.

Focus on lasers, imaging, and microscopy

Focus on lasers, imaging, and microscopy

Multifunctional transition metal doped Sb2O3 thin film with high near-IR transmittance, anti-reflectance and UV blocking features

We present optically modified Sb2O3 thin film as a multi-functional layer that can be used as UV blocking, Near Infrared (NIR) transmitting and anti-reflecting layer suited for solar energy harvesting. Optical modifications are achieved by transition metal (Mn, Ni and Cu) doping through vacuum evaporation and solid state grinding which introduces new sidewise outgrowths emerging on the previously reported thorn structure of the film. The new structures are found growing along [110] direction, reducing the growth of thorns along [111] direction. Though the UV absorbance and wavelength range of absorbance are larger for transition metal doped Sb2O3 thin films, their UV reflectance is very low compared to the undoped films. However, they all show very good absorption in UVB and UVC regions and partial absorption in UVA region like undoped Sb2O3 thin films. Ultraviolet Protection Factor of all the films lie in the range 25–50 showing their competent UV blocking ability. NIR transmittances of Sb2O3 thin film increases with Ni and Mn doping, making them appropriate for NIR transmitting layers in cover glass of IR sensors and solar thermal energy collectors. Considering the multi-functionality, the overall performance of transition metal doped Sb2O3 thin films are more efficient than undoped film.

Optical Applications of Nickel Sulphate Crystals at Elevated Temperature: A Characterization Study with the Addition of Amino Acid as an Impurity

L alanine added nickel sulphate hexahydrate (LANSH)crystals were grown by slow evaporation method in aqueous solution at room temperature. The grown crystals were characterized structurally, optically and thermally. X-ray diffraction studies proved the crystalline nature of the grown compound and it belongs to monoclinic structure. The presence of various functional groups was identified through FTIR analysis. The LANSH crystals are highly transparent in the mid UV wavelength range and hence these may be used in UV filters.In addition, thermo gravimetric analysis shows that the crystal is stable up to 110 °C. Therefore, LANSH can be employed in UV filters with higher ambient temperature too.

Protection against a wide UV wavelength range by Bragg reflection from polycrystalline colloidal photonic crystals

Polycrystalline colloidal crystals can block ultraviolet light of 290–400 nm, regardless of the incident angle, while maintaining transparency in the visible light region.

Optoelectronic UV Communication on Scattered Laser Radiation

Previous and new results on the problems of optical communication in scattered laser radiation in the UV wavelength range, obtained at the Institute of Atmospheric Optics, Siberian Branch, Russian Academy of Sciences, are discussed. Field experiments on optoelectronic communication in night- and daytime conditions in 2017 and 2018 are presented.

Perfect meta-absorber by using pod-like nanostructures with ultra-broadband, omnidirectional, and polarization-independent characteristics

The on-chip perfect meta-absorber (PMA) is an important optical and thermal energy component in photovoltaics, thermal emitters, and energy harvesting applications. However, most reported PMAs rely on the complicated lithography techniques, which imposed a serious cost barrier on the development of practical applications, especially in the visible to near-infrared (NIR) wavelength range and at very large scales. Importantly, it is hard to realize PMA in the UV wavelength range by using current lithography techniques. In this article, we develop an ultra-broadband PMA by using natural lithography (NL) technique. The morphology of proposed PMA is randomly distributed pod-like nanostructures composed of a nanocomposite (Au/SiO2) covered a gold layer. It can be formed easily on Si substrate to function as an ultra-broadband, omnidirectional, and polarization-independent PMA by controlling the conditions of sputtering deposition and thermal annealing treatment. We experimentally realized an on-chip ultra-broadband PMA with almost 100% absorption spanned from UV-visible to NIR wavelength ranges. This cost-effective and high-efficiency approach would release the manufacturing barrier for previously reported PMAs and therefore open an avenue to the development of effectively energy harvesting, energy recycling, and heat liberation applications.

An aposematic colour‐polymorphic moth seen through the eyes of conspecifics and predators – Sensitivity and colour discrimination in a tiger moth

Abstract Although predation is commonly thought to exert the strongest selective pressure on coloration in aposematic species, sexual selection may also influence coloration. Specifically, polymorphism in aposematic species cannot be explained by natural selection alone. Males of the aposematic wood tiger moth (Arctia plantaginis) are polymorphic for hindwing coloration throughout most of their range. In Scandinavia, they display either white or yellow hindwings. Female hindwing coloration varies continuously from bright orange to red. Redder females and yellow males suffer least from bird predation. White males often have higher mating success than yellow males. Therefore, we ask whether females can discriminate the two male morphs by colour. Males approach females by following pheromone plumes from a distance, but search visually at short range. This raises the questions whether males discriminate female coloration and, in turn, whether female coloration is also sexually selected. Using electroretinograms, we found significantly larger retinal responses in male than female A. plantaginis, but similar spectral sensitivities in both sexes, with peaks in the UV (349 nm), blue (457 nm) and green (521 nm) wavelength range. According to colour vision models, conspecifics can discriminate white and yellow males as separate morphs, but not orange and red females. For moths and birds (Cyanistes caeruleus), white males are more conspicuous against green and brown backgrounds, mostly due to UV reflectivity, and red females are slightly more conspicuous than orange females. The costly red coloration among females is likely selected by predator pressure, not by conspecifics, whereas male colour polymorphism is probably maintained, at least partly, by the opposing forces of predation pressure favouring yellow males, and female preference for white males. Whether or not the preference for white males is based on visual cues requires further testing. The evolution of polymorphic aposematic animals can be better understood when the visual system of the species and their predators is taken into consideration. A plain language summary is available for this article.

Tackling the Saturation of Oxygen: The Use of Phosphorus and Sulfur as Proxies within the Neutral Interstellar Medium of Star-forming Galaxies

Abstract The abundance of oxygen in galaxies is widely used in furthering our understanding of galaxy formation and evolution. Unfortunately, direct measurements of O/H in the neutral gas are extremely difficult to obtain, as the only O i line available within the Hubble Space Telescope (HST) UV wavelength range (1150–3200 Å) is often saturated. As such, proxies for oxygen are needed to indirectly derive O/H via the assumption that solar ratios based on local Milky Way sight lines hold in different environments. In this paper we assess the validity of using two such proxies, P ii and S ii, within more typical star-forming environments. Using HST-Cosmic Origins Spectrograph (COS) far-UV (FUV) spectra of a sample of nearby star-forming galaxies (SFGs) and the oxygen abundances in their ionized gas, we demonstrate that both P and S are mildly depleted with respect to O and follow a trend, log(P ii/S ii) , in excellent agreement with the solar ratio of over the large range of metallicities (0.03–3.2 Z ⊙) and H i column densities ( (H i)/cm−2] =18.44–21.28) spanned by the sample. From literature data we show evidence that both elements individually trace oxygen according to their respective solar ratios across a wide range of environments. Our findings demonst-rate that the solar ratios of and can both be used to derive reliable O/H abundances in the neutral gas of local and high-redshift SFGs. The difference between O/H in the ionized- and neutral gas phases is studied with respect to metallicity and H i content. The observed trends are consistent with galactic outflows and/or star formation inefficiency affecting the most metal-poor galaxies, with the possibility of primordial gas accretion at all metallicities.

Optoelectronic communication on scattered laser radiation in the UV wavelength range

Optoelectronic communication on scattered laser radiation in the UV wavelength range

Evaluation of a liquid crystal based polarization modulator for a space mission thermal environment

The Multi Element Telescope for Imaging and Spectroscopy (METIS) is one of the remote sensing instruments to be onboard the future NASA/ESA Solar Orbiter mission. The science nominal mission orbit will take the spacecraft from 0.28 to 0.95 astronomical units from the Sun, setting challenging and variable thermal conditions to its payload. METIS is an inverted-occultation coronagraph that will image the solar corona in the visible and UV wavelength range. In the visible light path a Polarization Modulation Package (PMP) performs a polarimetric analysis of the incoming solar light. This PMP is based on liquid crystal variable retarders (LCVR) and works under a temporal modulation scheme. The LCVRs behavior has a dependence on temperature and, as a consequence, it is critical to guarantee the PMP performance in the mission thermal environment. Key system specifications are the optical quality and the optical retardance homogeneity. Moreover, the thermally induced elastic deformations of the mechanical mounts and the LCVRs shall not produce any performance degradation. A suitable thermal control is hence required to maintain the system within its allowed limits at any time. The PMP shall also be able to reach specific set-points with the power budget allocated. Consequently, and in order to verify the PMP thermal design, we have experimentally reproduced the expected thermal flight environment. Specifically, a thermal-vacuum cycle test campaign is run at the different mission operational conditions. The purpose is both to check the stability of the thermal conditions and to study the optical quality evolution/degradation. Within this test transmitted wavefront measurements and functional verification tests have been carried out. To do that we adapted an optical interrogation scheme, based on a phase shifting interferometric technique, that allows for inspection of the PMP optical aperture. Finally, measurements obtained at non-operational temperature conditions are also shown. These results demonstrate that the device meets the specifications required to perform its operational role in the space mission environment.