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The diffuse cosmic background radiation in the Galaxy Evolution Explorer far-ultraviolet (FUV, 1300-1700 Å) is deduced to originate only partially in the dust-scattered radiation of FUV-emitting stars: the source of a substantial fraction of the FUV background radiation remains a mystery. The radiation is remarkably uniform at both far northern and far southern Galactic latitudes and increases toward lower Galactic latitudes at all Galactic longitudes. We examine speculation that this might be due to interaction of the dark matter with the nuclei of the interstellar medium, but we are unable to point to a plausible mechanism for an effective interaction. We also explore the possibility that we are seeing radiation from bright FUV-emitting stars scattering from a “second population” of interstellar grains—grains that are small compared with FUV wavelengths. Such grains are known to exist, and they scatter with very high albedo, with an isotropic scattering pattern. However, comparison with the observed distribution (deduced from their 100 μm emission) of grains at high Galactic latitudes shows no correlation between the grains' location and the observed FUV emission. Our modeling of the FUV scattering by small grains also shows that there must be remarkably few such “smaller” grains at high Galactic latitudes, both north and south; this likely means simply that there is very little interstellar dust of any kind at the Galactic poles, in agreement with Perry and Johnston. We also review our limited knowledge of the cosmic diffuse background at ultraviolet wavelengths shortward of Lyα—it could be that our “second component” of the diffuse FUV background persists shortward of the Lyman limit and is the cause of the reionization of the universe. [ABSTRACT FROM AUTHOR]

The aurorae at Jupiter are made up of many different features associated with a variety of generation mechanisms. The main auroral emission, also known as the main oval, is the most prominent of them as it accounts for approximately half of the total power emitted by the aurorae in the ultraviolet range. The energy of the precipitating electrons is a crucial parameter to characterize the processes at play which give rise to these auroral emissions, and the altitude of the emissions directly depends on this energy. Here we make use of far-UV (FUV) images acquired with the Advanced Camera for Surveys on board the Hubble Space Telescope and spectra acquired with the Space Telescope Imaging Spectrograph to measure the vertical profile of the main emissions. The altitude of the brightness peak as seen above the limb is ~ 400 km, which is significantly higher than the 250 km measured in the post-dusk sector by Galileo in the visible domain. However, a detailed analysis of the effect of hydrocarbon absorption, including both simulations and FUV spectral observations, indicates that FUV apparent vertical profiles should be considered with caution, as these observations are not incompatible with an emission peak located at 250 km. The analysis also calls for spectral observations to be carried out with an optimized geometry in order to remove observational ambiguities. [ABSTRACT FROM AUTHOR]

The main auroral emission at Jupiter generally appears as a quasi-closed curtain centered around the magnetic pole. This auroral feature, which accounts for approximately half of the total power emitted by the aurorae in the ultraviolet range, is related to corotation enforcement currents in the middle magnetosphere. Early models for these currents assumed axisymmetry, but significant local time variability is obvious on any image of the Jovian aurorae. Here we use far-UV images from the Hubble Space Telescope to further characterize these variations on a statistical basis. We show that the dusk side sector is ~ 3 times brighter than the dawn side in the southern hemisphere and ~ 1:1 brighter in the northern hemisphere, where the magnetic anomaly complicates the interpretation of the measurements. We suggest that such an asymmetry between the dawn and the dusk sectors could be the result of a partial ring current in the nightside magnetosphere. [ABSTRACT FROM AUTHOR]

We have demonstrated the photon-stimulated surface spectroscopy using broadband vacuum ultraviolet (VUV) emissions from a laser-produced plasma, in which adsorbed atoms or molecules on material surfaces were to be desorbed and dissociated as a result of absorption of the wavelength-selected VUV photons. Desorbed and dissociated atoms or molecules were then detected by a mass spectrometer. Mass spectra of polyethylene and polyvinyl chloride samples were obtained as a function of the irradiation wavelength. We have found sufficient characteristic differences of the mass spectra in the irradiation wavelength shorter than 200 nm in each sample. The desorption and dissociation of atoms or molecules from material surfaces depended on bond energy or molecular structure. [ABSTRACT FROM AUTHOR]

Corrosion-, chemical-resistant pure iron thin films were formed by the vacuum ultraviolet fluorine laser of 157 nm wavelength induced surface modification of 30- to 50-nm-thick iron thin films. Transmission electron microscope and electron energy-loss spectroscopy were conducted to analyze structure and oxidation state of the thin modified layer of iron thin films. No rust was observed on the surface of the fluorine laser-irradiated iron thin films in air for 2 years. The samples also showed high chemical resistance to a HNO aqueous solution to fabricate a micropattern of pure iron thin films. [ABSTRACT FROM AUTHOR]

Thin organic films with oxygen-bearing functional groups (hydroxyl, carboxyl, ...) were prepared by 'co-polymerizing' gas mixtures of ethylene (C2H4) and one of several O-containing oxidizer molecules, O2, CO2, or N2O. This was done either by vacuum-ultraviolet (VUV) photo-polymerization or by low-pressure r.f. plasma-assisted CVD. The gas mixture ratio, R, permits one to control total oxygen concentration, [O], as well as the relative proportions of the various functionalities. Analyses were performed by XPS (with or without chemical derivatization using TFAA to determine [OH] content), and IRRAS-FTIR. Temporal and structural stability (mass change) of deposits under exposure to air or water was examined; altogether, data confirmed different reaction pathways for VUV and PECVD. [ABSTRACT FROM AUTHOR]

Vacuum ultraviolet (VUV) radiation around 159 nm is obtained toward direct excitation of a single trapped $$^{115}\hbox {In}^{+}$$ ion. An efficient fluoride-based VUV output coupler is employed for intracavity high-harmonic generation of a Ti:S oscillator. Using this coupler, where we measured its reflectance to be about 90 %, an average power reaching 6.4 $$\upmu$$ W is coupled out from a modest fundamental power of 650 mW. When a single comb component out of 1.9 $$\times$$ 10 $$^{5}$$ teeth is resonant to the atomic transition, 100s of fluorescence photons per second will be detectable under a realistic condition. [ABSTRACT FROM AUTHOR]

A high-speed tangentially viewing vacuum ultraviolet (VUV) telescope system, using an inverse Schwarzschild-type optic system was developed to study fluctuations in the Large Helical Device (LHD). However, for the original system, the sampling rate was restricted to below 2000 Hz due to the low signal to noise (S/N) ratio in the experiment. In order to improve the S/N ratio, upgrade of the system was made. With this upgraded optical system, the maximum framing rate is improved to 6000 fps with a similar spatial resolution. Rotation of the m = 2 structure caused by the magnetohydrodynamic (MHD) instability is measured by the upgraded system. The spatial structure of the image is consistent with the synthetic image assuming the interchange mode type displacement of the flux surfaces. [ABSTRACT FROM AUTHOR]

The fabrication of Ce3+-doped lutetium oxyorthosilicate (Lu2SiO5:Ce, LSO:Ce) scintillation ceramics was investigated by pressureless sintering starting from synthetic submicrometer polycrystalline LSO:Ce powder. It was found that translucent LSO ceramics were densified successfully with relative density of 99.5% under sintering condition of 1720 °C for 4 h. As-sintered LSO ceramics were pore-free with average grain size of 5 μm and exhibited a translucent state. The broad emission spectra centered at 419 nm of the LSO:Ce ceramics under vacuum ultraviolet (VUV) and UV excitation at room temperature. Under x-ray excitation, the overall emission intensity of obtained LSO ceramics achieved twice of that of bismuth germanium oxide (also known as bismuth germanate) single crystal at room temperature. Under excitation of 356 nm and emission of 420 nm, the luminescence decay time of the obtained LSO scintillation ceramics reached only 21.2 ns. The light yield of the LSO ceramics was 21,300 ph/MeV, which reached 91% of that of LSO single crystal. [ABSTRACT FROM PUBLISHER]

Ar+ ion bombardment (900 eV) of organosilicate glass (OSG) in the presence of NH3 (1x10-6 Torr) yields an overlayer containing Si-NHx bonds. The NHx layer decreases the rate of carbon loss from the remaining film upon subsequent oxygen plasma exposure, due to preferential removal of N from the surface region. Ab initio density functional theory calculations have been performed to investigate the stability of the bonds present in low-k dielectrics utilizing a trimethyltrisiloxane model system. Calculated bond energies are 6.30 eV (Si-NH2), 6.27 eV (Si-OH), 5.69 eV (Si-CH3), and 5.54 eV (Si-H). The slightly higher calculated Si-NH2 bond energy is consistent with experiment and indicates that the nitrided OSG surface layer inhibits carbon loss in part by inhibition of O2 diffusion into the bulk. [ABSTRACT FROM AUTHOR]

This article aims to elucidate on usefulness of vacuum ultraviolet (VUV) for photoreductive degradation of perfluorooctanoic acid (PFOA), a representative perfluorinated compound (PFC), in water for the first time. Bench-scale tests were conducted on oxidative and reductive (with aquated electron: e) mineralization of PFOA using low-pressure UV (LPUV) lamps and potassium iodide. Unlike with 254 nm wavelength (UVC), the reductive mineralization with VUV was very inefficient compared to the corresponding oxidative mineralization. The inefficiency is attributed to low reactivity of e with PFOA and its fluorinated products than that of 185 nm photons. Direct VUV photolysis of PFOA and its products in reductive reaction conditions was not apparent due to a very big difference in reactivity of 185 and 254 nm photons with iodide. The results demonstrated that highly energetic VUV photons are not suitable for photoreductive degradations of PFCs involving e, but they can be best used for oxidative degradations. These findings should serve as an important reference on VUV usage to decompose refractory micropollutants. [ABSTRACT FROM AUTHOR]

The generation of high-order harmonics and attosecond pulses at ultrahigh repetition rates (>1 MHz) promises to revolutionize ultrafast spectroscopy. Such vacuum ultraviolet (VUV) and soft X-ray sources could potentially be driven directly by plasmonic enhancement of laser pulses from a femtosecond oscillator, but recent experiments suggest that the VUV signal is actually dominated by incoherent atomic line emission. Here, we demonstrate a new regime of phase-matched below-threshold harmonic generation, for which the generation and phase matching is enabled only near resonance structures of the atomic target. The coherent VUV line emission exhibits low divergence and quadratic growth with increasing target density up to nearly 1,000 torr mm and can be controlled by the sub-cycle field of a few-cycle driving laser with an intensity of only ∼1 × 1013 W cm−2, which is achievable directly from few-cycle femtosecond oscillators with nanojoule energy. [ABSTRACT FROM AUTHOR]

Vacuum ultraviolet (VUV) laser systems for advanced applications such as micro and precise processing and photochemical reactions have been developed. We have been constructing a VUV-MOPA system to generate output energy of sub-mJ with a pulse width of sub-picosecond at the wavelength of 126 nm. A VUV seed pulse, generated by the 7th harmonics of a 882 nm Ti:Sapphire (TiS) laser was amplified by the Ar2 medium generated from an optical-field-induced ionization of Ar plasma pumped by the TiS laser. We achieved an amplification of 126 nm seed pulse by a factor of 2.6. Recently, we introduced a new 800 nm TiS laser. This laser was synchronized with the 882 nm TiS laser and the delay between these outputs was controllable. We also developed a photo-stimulated desorption spectroscopy method for surface analysis. A tunable incoherent VUV radiation obtained from a laser induced plasma was irradiated the samples and then desorbed species were analyzed by mass spectroscopy. This method enables analysis without sample heating and damaging. [ABSTRACT FROM AUTHOR]

Electromagnetic metamaterials offer a significant potential to enable new capabilities in many applications. Under high-power illumination, metamaterials and periodic structures experience internal breakdown, altering frequency response, and/or yielding thermal damage. Our prior research observed simultaneous breakdown discharges at two separate sites within a multiresonator metamaterial unit cell, even though the electric field intensities at one of the resonator sites should have been well below the threshold intensity required for breakdown. Here, we investigate three candidate mechanisms for the simultaneous breakdown discharges: energetic electrons, ultraviolet (UV) radiation, and vacuum UV (VUV) radiation. Experiments inserting different dielectric barriers between the two resonators of a multiresonator unit cell were able to selectively isolate the coupling influence of the candidate mechanisms. It was established that, VUV radiation from the discharge at the resonator with a lower electric field breakdown threshold causes simultaneous breakdown at the other resonator where the field intensities are otherwise too low to induce breakdown. [ABSTRACT FROM PUBLISHER]

Context. Dust grains absorb the interstellar far ultra-violet and visible photons and re-emit them in far-infrared (FIR) wavebands. The dust FIR continuum can be predicted by a grid of models using various values of the interstellar radiation field. Aims. We analyze the dust continuum emission in two Hi-GAL science-demonstration phase (SDP) fields using both the radiative transfer code, Cloudy, and the DustEM dust model, to explore the effect of radiative transfer on dust temperature. The 500 μm submillimeter excess emission and the very small grain (VSG) contribution to the 70 μm intensity are investigated by spectral energy distribution (SED) fitting using the Cloudy model. Methods. By comparing the observation with the model prediction, we derive dust temperature maps of the two SDP fields by fitting the dust SED with 4-band data (SPIRE bands plus PACS 160 μm) using both Cloudy and DustEM models. Considering radiative transfer and grain physics simultaneously, we investigate the existence of a 500 μm excess and estimate the VSG contribution to the 70 μm intensity by fitting the dust SED with 3-band data (160, 250, and 350 μm) and 5-band data (SPIRE and PACS bands), respectively. Results. We confirm that the field with star formation activities have a higher temperature (18.7 ± 0.9 K) than the quiescent region (15.2±0.6 K).We find that the radiative transfer affects the FIR SED of the SDP fields and results in a higher temperature distribution than the dust-only model fit. There is no significant detection of a 500 μm excess in the two SDP fields. The relative contribution from the VSGs to the 70 μm intensity can be up to 50%. [ABSTRACT FROM AUTHOR]

The threshold values of the annual fluence of atomic oxygen ( F ≈ 10 cm), as well as the ratios of the energy-flux density of vacuum ultraviolet radiation of the solar spectrum to the flux density of atomic oxygen (Φ/Φ ≈ 8 × 10 mJ) were determined, which are characterized the influence of the synergistic effect on the mass loss of Kapton-H, PM-A, and PM-1E polyimide films, which are spacecraft materials. [ABSTRACT FROM AUTHOR]

Context. The vacuum-UV (VUV) absorption cross sections of most molecular solids present in interstellar ice mantles with the exception of H2O, NH3, and CO2 have not been reported yet. Models of ice photoprocessing depend on the VUV absorption cross section of the ice to estimate the penetration depth and radiation dose, and in the past, gas phase cross section values were used as an approximation. Aims. We aim to estimate the VUV absorption cross section of molecular ice components. Methods. Pure ices composed of CO, H2O, CH3OH, NH3, or H2S were deposited at 8 K. The column density of the ice samples was measured in situ by infrared spectroscopy in transmittance. VUV spectra of the ice samples were collected in the 120-160 nm (10.33-7.74 eV) range using a commercial microwave-discharged hydrogen flow lamp. Results. We provide VUV absorption cross sections of the reported molecular ices. Our results agree with those previously reported for H2O and NH3 ices. Vacuum-UV absorption cross section of CH3OH, CO, and H2S in solid phase are reported for the first time. H2S presents the highest absorption in the 120-160 nm range. Conclusions. Our method allows fast and readily available VUV spectroscopy of ices without the need to use a synchrotron beamline. We found that the ice absorption cross sections can be very different from the gas-phase values, and therefore, our data will significantly improve models that simulate the VUV photoprocessing and photodesorption of ice mantles. Photodesorption rates of pure ices, expressed in molecules per absorbed photon, can be derived from our data. [ABSTRACT FROM AUTHOR]

We report measurements of the vacuum ultraviolet (VUV) emission spectra of a microwave-discharge hydrogen-flow lamp (MDHL), a common tool in astrochemistry laboratories working on ice VUV photoprocessing. The MDHL provides hydrogen Ly-α (121.6 nm) and H2 molecular emission in the 110-180 nm range. We show that the spectral characteristics of the VUV light emitted in this range, in particular the relative proportion of Ly-α to molecular emission bands, strongly depend on the pressure of H2 inside the lamp, the lamp geometry (F type versus T type), the gas used (pure H2 versus H2 seeded in He), and the optical properties of the window used (MgF2 versus CaF2). These different configurations are used to study the VUV irradiation of CO ice at 14 K. In contrast to the majority of studies dedicated to the VUV irradiation of astrophysical ice analogs, which have not taken into consideration the emission spectrum of the MDHL, our results show that the processes induced by photons in CO ice from a broad energy range are different and more complex than the sum of individual processes induced by monochromatic sources spanning the same energy range, as a result of the existence of multistate electronic transitions and discrepancy in absorption cross sections between parent molecules and products in the Ly-α and H2 molecular emission ranges. [ABSTRACT FROM AUTHOR]

Continuous coherent radiation in the vacuum ultraviolet at 122 nm (Lyman-α) can be generated using sum-frequency mixing of three fundamental laser beams in mercury vapor. One of the fundamental beams is at 254 nm wavelength, which is close to the 6 1S0–6 3P1 resonance in mercury. Experiments have been performed to investigate the effect of this one-photon resonance on phase-matching, absorption and the nonlinear yield. The efficiency of continuous Lyman-α generation has been improved by a factor of 4.5. [ABSTRACT FROM AUTHOR]

Direct current (dc) microhollow cathode discharge (MHCD) is an intense source for excimer radiation in vacuum ultraviolet at a wavelength of 172 nm in a high pressure xenon (Xe) gas. The concentration of precursors for the excimer formation, i.e., excited and ionized gas atoms, increases significantly by applying high voltage pulse onto the dc MHCD over the pulse duration range from 20 to 100 ns. The intensity of the excimer emission for the voltage pulse of 20 ns duration exceeds that of the emission intensity obtained from the same MHCD operated only in the dc mode, by one order of magnitude. In addition, the emission intensity increases by one order of magnitude over the pulse duration range from 20 to 100 ns. It can be assumed that the emission intensity of the MHCD source increases as long as the duration of the high voltage pulse is shorter than the electron relaxation time. For the high voltage pulse of 100 ns duration, the emission intensity has been found to be further enhanced by a factor of three when the gas pressure is increased from 200 to 800 mbar. [ABSTRACT FROM AUTHOR]