Search

MgO crystals have been exposed to vacuum ultraviolet (VUV) radiation from a synchrotron, with energies up to 9 eV, and the emitted light, at wavelengths above 200 nm, was observed. It is concluded that bulk excitons, play an important role in the diffusion of energy inside MgO crystals, resulting in 5.85 eV (212 nm) emission from the MgO terraces of large (0.2-2 μm) MgO: F crystals. In the case of aliovalent impurity doping, then the bulk exciton energy is also transferred to the Vk centres and 5.3 eV (235 nm) light is emitted. Both fluorine and silicon doping appear to promote UV surface emission, acting similarly to an ns2 ion inside MgO, while strong scandium doping is killing the surface emission completely. The 212 nm surface UV emission and the 235 nm bulk UV emission can be excited only at the bandgap edge. Broadband visible light, centred around 400 nm, is also emitted. Contrary to the UV emission, this is not generated when excited at the bandgap edge; instead, we find that it is only excited at sub-bandgap energies, with a maximum at the 5C surface excitation energy of 5.71 eV (217 nm) for the MgO terraces. [ABSTRACT FROM AUTHOR]

The pyrolysis process of pine wood, a promising biofuel feedstock, has been studied with tunable synchrotron vacuum ultraviolet photoionization mass spectrometry. The mass spectra at different photon energies and temperatures as well as time-dependent profiles of several selected species during pine wood pyrolysis process were measured. Based on the relative contents of three lignin subunits, the data indicate that pine wood is typical of softwood. As pyrolysis temperature increased from 300 to 700 °C, some more details of pyrolysis chemistry were observed, including the decrease of oxygen content in high molecular weight species, the observation of high molecular weight products from cellulose chain and lignin polymer, and potential pyrolysis mechanisms for some key species. The formation of polycyclic aromatic hydrocarbons (PAHs) was also observed, as well as three series of pyrolysis products derived from PAHs with mass difference of 14 amu. The time-dependent profiles show that the earliest products are formed from lignin, followed by hemicellulose products, and then species from cellulose. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

The fourth harmonic emission (200 nm) of a femtosecond Ti:sapphire laser (35 fs) was generated and used in the multiphoton ionization of 49 pesticides in gas chromatography/time-of-flight mass spectrometry. The limit of detection was improved when the ionization source from the third harmonic emission (267 nm) was replaced with the fourth harmonic emission for several pesticide molecules that contained no conjugated double bonds since their absorption bands are located in the far-ultraviolet region. This analytical instrument was used in the analysis of a series of real samples including potatoes, carrots, and cabbage, and a signal suspected to arise from di-allate was observed for the potato sample.[Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

We present an analysis of 98 galaxies of low-dust content, selected from the Spitzer Local Volume Legacy survey, aimed at examining the relation between the ultraviolet (UV) color and dust attenuation in normal star-forming galaxies. The IRX–β diagram relates the total dust attenuation in a galaxy, traced by the far-IR (FIR) to UV ratio, to the observed UV color, indicated by β. Previous research has indicated that while starburst galaxies exhibit a relatively tight IRX–β relation, normal star-forming galaxies do not, and have a much larger spread in the total-IR to far-UV (FUV) luminosity for a fixed UV color. We examine the role that the age of the stellar population plays as the “second parameter” responsible for the observed deviation and spread of star-forming galaxies from the starburst relation. We model the FUV to FIR spectral energy distribution of each galaxy according to two broad bins of star formation history (SFH): constant and instantaneous burst. We find clear trends between stellar population mean age estimators (extinction-corrected FUV/NIR, U−B, and EW(Hα)) and the UV color β; the trends are mostly driven by the galaxies best-described by instantaneous burst populations. We also find a significant correlation between β and the mean age directly determined from the best-fit instantaneous models. As already indicated by other authors, the UV attenuation in star-forming galaxies may not be recovered with the UV color alone and is highly influenced by the stellar population’s mean age and SFH. Overall, the scatter in the IRX–β diagram is better correlated with β than with the perpendicular distance, dp. [ABSTRACT FROM AUTHOR]

For many years, our group has been investigating the VUV spectroscopy and photochemistry of molecules of astrophysical (Jochims et al. 2006a,b; Leach et al. 2008; Schwell et al. 2012) and prebiotic interest (Schwell et al. 2006). Polyynes and cyano-polyynes that are abundant in the interstellar medium (ISM) and in planetary atmospheres, have been investigated too (e.g. Fray et al. 2010). An aerosol source for reactive and thermo-labile compounds has been developed (Gaie-Levrel et al. 2011) to perform gas-phase measurements. These are necessary to measure intrinsic molecular properties and to compare to quantum chemical calculations. Besides measuring absolute absorption and photoionization cross sections, dissociative channels and their involved excited states are identified for a number of molecules of interstellar interest. Branching ratios of the respective elementary photoreactions are determined in order to understand and model the photochemistry occurring in the ISM. Some very recent results on the dissociative photoionization of methylformate (MF), glycolaldehyde (GA), dimethylether (DIM), aminoacetonitrile (AAC) and cyanoacetylene (CA), are presented here. [ABSTRACT FROM AUTHOR]

We investigate the absorption-dispersion spectra of a weak signal field probing a system of 2-level atom coherently driven by a non-resonant mono- or bi-chromatic laser field of arbitrary strength and damped by a non-resonant squeezed vacuum radiation reservoir. In particular, we utilize our iterative analytic solutions of the non-autonomous model Bloch equations to obtain computationally the zero-absorption isolines in the (Δ, Ω)-plane at resonant or Rabi-side probe field frequency (Δ = atomic frequency detuning, Ω = Rabi frequency of the driving field). By product, the accompanied regions of finite or steep variation dispersion are identified. [ABSTRACT FROM AUTHOR]

Tb-activated SrGd(BO) green phosphors were prepared by conventional solid-state reaction. The vacuum ultraviolet (VUV) excitation, photoluminescence (PL) and decay properties of the phosphors in the visible range were investigated. The excitation spectrum showed a strong broad band from 160 to 200 nm with a maximum at 183 nm which was adjacent to the VUV excitation light source of 172 nm. Under excitation at 172 nm, the optimum co-doping concentration of Tb was 10 mol%, and the emission intensity of SrGd(BO):0.1Tb was comparable to that of commercial ZnSiO:Mn. The strongest emission peak of SrGd(BO):0.1Tb was at 543 nm with chromaticity coordinates of (0.2626, 0.4922) and a lifetime of 2.32 ms. The optical properties of the green phosphor SrGd(BO): Tb make it suitable for use in Hg-free fluorescent lamps and plasma display panels. [ABSTRACT FROM AUTHOR]

The article discusses how a 45° grazing angle and an SiC, silicon carbide, coating on silica as an optimized configuration on a spectrometer is used for covering the vacuum-ultraviolet range. The system supports the collection of high-resolution emission spectroscopy data. It also helps a large user community for investigating photoabsorption processes involving valence and inner-valence shell excitation in the vacuum-ultraviolet range.

A next-generation vacuum-ultraviolet (Lyman-alpha) absorption hygrometer for high-rate research aircraft humidity measurements designed by the National Center for Atmospheric Research is described. It retains the high data rate, optical and mechanical simplicity, and low maintenance of previous Lyman-alpha hygrometers, while incorporating modern electronics and rugged, long-lived commercially available lamps and detectors. The mass of the sensing head is 2.0 kg in a volume of 3700 cm³, while the power supply is 1.3 kg mass in a volume of 1100 cm³. Power draw is 0.2 A at 120 V alternating current (AC). In bench and aircraft flight testing the prototype shows a bandwidth of 35 Hz and mixing ratio noise of ±0.5% over a water vapor mixing ratio range of 2-15 g kg-1. This range can be scaled to lower mixing ratios by increasing the path-length. This performance enables measurements of water vapor concentration with high spatial resolution from research aircraft. The prototype instrument has flown over 380 h with minimal maintenance or repairs. [ABSTRACT FROM AUTHOR]

We present GALEX far-ultraviolet (FUV) and near-ultraviolet (NUV) as well as SDSS g, r, i photometry and structural parameters for the Herschel Reference Survey, a magnitude-, volume-limited sample of nearby galaxies in different environments. We use this unique dataset to investigate the ultraviolet (UV) structural scaling relations of nearby galaxies and to determine how the properties of the UV disk vary with atomic hydrogen content and environment. We find a clear change of slope in the stellar mass vs. effective surface brightness relation when moving from the optical to the UV, with more massive galaxies having brighter optical but fainter UV surface brightnesses than smaller systems. A similar change of slope is also seen in the radius vs. surface brightness relation. By comparing our observations with the predictions of a simple multi-zone chemical model of galaxy evolution, we show that these findings are a natural consequence of a much more efficient inside-out growth of the stellar disk in massive galaxies. We confirm that isophotal radii are always a better proxy for the size of the stellar/star-forming disk than effective quantities and we show that the extent of the UV disk (normalized to the optical size) is strongly correlated to the integrated Hi gas fraction. This relation still holds even when cluster spirals are considered, with Hi-deficient systems having less extended star-forming disks than Hi-normal galaxies. Interestingly, the star formation in the inner part of Hi-deficient galaxies is significantly less affected by the removal of the atomic hydrogen, as expected in a simple ram-pressure stripping scenario. These results suggest that it is the amount of Hi that regulates the growth of the star-forming disk in the outskirts of galaxies. [ABSTRACT FROM AUTHOR]

Context. The 30 Dor region in the Large Magellanic Cloud (LMC) is the most vigorous star-forming region in the Local Group. Star formation in this region is taking place in low-metallicity molecular gas that is exposed to an extreme far-ultraviolet (FUV) radiation field powered by the massive compact star cluster R136. 30 Dor is therefore ideally suited to study the conditions in which stars formed at earlier cosmological times. Aims. Observations of (sub)mm and far-infrared (FIR) spectral lines of the main carbon-carrying species, CO, [C I] and [C II], which originate in the surface layers of molecular clouds illuminated by the FUV radiation of young stars, can be used to constrain the physical and chemical state of the star-forming ISM. Methods. We used the NANTEN2 telescope to obtain high-angular resolution observations of the 12CO J = 4 → 3, J = 7 → 6, and 13CO J = 4 → 3 rotational lines and [C I] 3P1- 3P0 and 3P2- 3P1 fine-structure submillimeter transitions in 30 Dor-10, the brightest CO and FIR-emitting cloud at the center of the 30 Dor region. We derived the physical and chemical properties of the low-metallicity molecular gas using an excitation/radiative transfer code and found a self-consistent solution of the chemistry and thermal balance of the gas in the framework of a clumpy cloud PDR model. We compared the derived properties with those in the N159W region, which is exposed to a more moderate far-ultraviolet radiation field compared with 30 Dor-10, but has similar metallicity. We also combined our CO detections with previously observed low-J CO transitions to derive the CO spectral-line energy distribution in 30 Dor-10 and N159W. Results. The separate excitation analysis of the submm CO lines and the neutral carbon fine structure lines shows that the mid-J CO and [C I]-emitting gas in the 30 Dor-10 region has a temperature of about 160 K and a H2 density of about 104 cm-3. We find that the molecular gas in 30 Dor-10 is warmer and has a lower beam filling factor compared to that of N159W, which might be a result of the effect of a strong FUV radiation field heating and disrupting the low-metallicity molecular gas. We use a clumpy PDR model (including the [C II] line intensity reported in the literature) to constrain the FUV intensity to about X0 ≈ 3100 and an average total H density of the clump ensemble of about 105 cm-3 in 30 Dor-10. [ABSTRACT FROM AUTHOR]

The 7.8 eV nuclear isomer transition in 229thorium has been suggested as a clock transition in a new type of optical frequency standard. Here we discuss the construction of a 'solid-state nuclear clock' from thorium nuclei implanted into single crystals transparent in the vacuum ultraviolet range. We investigate crystal-induced line shifts and broadening effects for the specific system of calcium fluoride. At liquid nitrogen temperatures, the clock performance will be limited by decoherence due to magnetic coupling of the thorium nuclei to neighboring nuclear moments, ruling out the commonly used Rabi or Ramsey interrogation schemes. We propose clock stabilization based on a fluorescence spectroscopy method and present optimized operation parameters. Taking advantage of the large number of quantum oscillators under continuous interrogation, a fractional instability level of 10-19 might be reached within the solid-state approach. [ABSTRACT FROM AUTHOR]

Cyclic dipeptides, due to their chemical properties and various bioactivities, are very attractive for medicinal chemistry. Fragmentations of three simple cyclic dipeptides including cyclo(Gly-Gly), cyclo(Ala-Ala) and cyclo(Gly-Val) in the gas-phase are determined with synchrotron vacuum ultraviolet (VUV) photoionization mass spectrometry (VUV PIMS) and theoretical calculations. Cyclo(Gly-Gly) and cyclo(Ala-Ala) show the similar fragmentation pathways. The primary decomposition reactions of cyclo(Gly-Gly) and cyclo(Ala-Ala) radical cations are found to be HNCO loss and CO elimination. The appearance energies (AEs) of fragment ions [CHNHCOCH] and [CHCHNHCOCHCH] are measured to be 10.21 and 9.66 ± 0.05 eV, respectively, which are formed from cyclo(Gly-Gly) and cyclo(Ala-Ala) radical cations with HNCO elimination. Due to the stabilization of the radical cation of cyclo(Gly-Val) with isopropyl side group, the dominant fragment ion m/ z 114 assigned as [CHNO] is produced by γ-H migration and i cleavage to lose propylene. The ionization energies (IEs) of three cyclic dipeptides decrease in the order cyclo(Gly-Gly) (9.33 ± 0.05 eV) > cyclo(Ala-Ala) (9.21 ± 0.05 eV) > cyclo(Gly-Val) (9.09 ± 0.05 eV) from measurements of photoionization efficiency spectra. It implies that IEs of cyclic dipeptides are affected by substituent groups and symmetrical characterization of molecular structures. These observations of the chemical properties of cyclic dipeptides radical ion (M) may be important for understanding gas-phase molecular reactivity of 2,5-diketopiperazines and guiding diketopiperazine-based drug design. [ABSTRACT FROM AUTHOR]

The hydrogen peroxide production upon vacuum ultraviolet (VUV) irradiation of water is reviewed, because published results from the last 10 years lead to conflicting mechanistic interpretations. This work confirms that in pure water, hydrogen peroxide is only produced in the presence of molecular oxygen. Mechanistic schemes explain these findings and confirm earlier statements that recombination of hydroxyl radicals is kinetically disfavoured. In agreement with other recent publications, this work confirms that enhanced hydrogen peroxide production takes place upon VUV irradiation of aqueous solutions of organic compounds. For these investigations, methanol was chosen as an organic model compound. During photolyses, hydrogen peroxide, dissolved molecular oxygen, pH-value of the reaction system, methanol and its products of oxidative degradation were analyzed, and kinetic studies were undertaken to explain the evolution of the concentrations of these components. [ABSTRACT FROM AUTHOR]

Anewdiagnostic method with tracer-encapsulated solid pellet (TESPEL) injection with multiple tracers is developed to study impurity behaviour in a magnetically confined plasma. If a pellet contains multiple tracers, it becomes possible to compare the behaviour of different impurities simultaneously under the same plasma conditions. We injected a TESPEL into the Large Helical Device mainly with triple tracers: vanadium (V), manganese (Mn) and cobalt (Co). The Li-like lines in the vacuum ultraviolet range and the K&agr; lines in the soft x-ray range from these tracers are simultaneously observed with a time resolution of 50 ms. As the charges of the nuclei of intrinsic impurities, chromium (Cr) and iron (Fe), are in between those of the tracers, the behaviour of Cr and Fe can be studied quantitatively by knowing the number of tracer particles and also by comparing the emission intensity change due to the electron temperature change. It is observed that the tracer impurities remain in the plasma core region when the plasma density is higher than 5*1019 m-3. It is also observed that the intrinsic impurities cannot enter the core region when the plasma density is higher than the same level, although the two phenomena appear to be independent. [ABSTRACT FROM AUTHOR]

The commercial vacuum ultraviolet (VUV) red phosphor (Y, Gd)BO3:Eu3+ has low luminous efficiency and poor color purity. Our work aims to overcome this drawback and we mainly devote to investigating the luminescence mechanism, improving the commercial red phosphor, and seeking for new red emitting VUV materials with high efficiency. Based on the investigation of the photoluminescence mechanism of VUV phosphors, both the luminous efficiency and the color purity of (Y, Gd)BO3:Eu3+ are improved. Additionally, a series of novel VUV red phosphors have been developed, such as (Gd,Y)Al3(BO3)4:Eu3+ and (La,Gd)P3O9:Eu3+. This presentation is a review about the recent research progress of red phosphors for plasma displays (PDPs) applications in our group. [ABSTRACT FROM AUTHOR]

We have demonstrated proof-of-principle of an incoherent ArF ∗ emission source with a quasi-point emission geometry using a laser-produced plasma in an Ar/F 2/He/Ne mixed gas. The VUV emission characteristics, such as the emission size, were dependent on those of the plasma-initiating laser. The average emission power was 10 μW at a repetition rate of 10 Hz at 193 nm. The average power conversion efficiency of the 193-nm emission from the plasma-initiating Nd:YAG laser was 6.3×10 −6. The average emission power at 193 nm was proportional to that of the plasma-initiating laser, indicating the scaling of the emission source. [ABSTRACT FROM AUTHOR]

The luminous efficiency and lifetime of plasma display panels (PDPs) are directly related to the performance of phosphors used in PDPs, thus higher efficiency, higher stability against high temperature processes and a long lifetime along with good color chromaticity against vacuum-ultraviolet (VUV) radiation are major concerns in selecting suitable phosphors for PDPs. In the same pursuit, we have developed the nano-sized (15-40 nm) BAM:Eu, YAG:Tb and YAG:Eu as blue, green and red phosphors and studied their luminescence properties under VUV excitations. In BAM:Eu, the 5d-excitation of Eu ions are found strongly dependent on the crystal field strength and Eu occupy lattice 'sites I' by substituting Ba ions. Whereas, in YAG:Tb, the observed green luminescence is assigned to D→F transitions (j = 3-6) due to electric dipole-dipole interaction, while, YAG:Eu shows strong red luminescence corresponding to D→F transition. Time evolution studies along with decay time calculations are further employed to verify the sustainable emission without quenching. [ABSTRACT FROM AUTHOR]

Aims. We investigate the global galaxy evolution over ~12 Gyr (0.05 ⩽ z ⩽ 4.5), from the far ultraviolet (FUV) luminosity function (LF), luminosity density (LD), and star formation rate density (SFRD), using the VIMOS-VLT Deep Survey (VVDS), a single deep galaxy redshift survey with a well controlled selection function. Methods. We combine the VVDS Deep (17.5 ⩽ IAB ⩽ 24.0) and Ultra-Deep (23.00 ⩽ i' AB ⩽ 24.75) redshift surveys, totalizing ~11 000 galaxies, to estimate the rest-frame FUV LF and LD, using a wide wavelength range of deep photometry (337 < λ < 2310 nm).We extract the dust attenuation of the FUV radiation, embedded in the well-constrained spectral energy distributions. We then derive the dust-corrected SFRD. Results. We find a constant and flat faint-end slope a in the FUV LF at z < 1.7. At z > 1.7, we set a steepening with (1+z). The absolute magnitude M☉ FUV steadily brightens in the entire range 0 < z < 4.5, and at z > 2 it is on average brighter than in the literature, while ϕ" is on average smaller. The evolution of our total LD shows a peak at z ≃ 2, clearly present also when considering all sources of uncertainty. The SFRD history peaks as well at z ≃ 2. It first steadily rises by a factor of ~6 during 2 Gyr (from z = 4.5 to z = 2), and then decreases by a factor of ~12 during 10 Gyr down to z = 0.05. This peak is mainly produced by a similar peak within the population of galaxies with -21.5 ⩽ MFUV ⩽ -19.5. As times goes by, the total SFRD is dominated by fainter and fainter galaxies. The mean dust attenuation of the global galaxy population rises fast by 1 mag during 2 Gyr from z ≃ 4.5 to z ~ 2, reaches slowly its maximum at z ≃ 1 (AFUV ≃ 2.2 mag), and then decreases by 1.1 mag during 7 Gyr down to z ≃ 0. Conclusions. We have derived the cosmic SFRD history and the total dust amount in galaxies over a continuous period of ~12 Gyr, using a single homogeneous spectroscopic redshift sample. The presence of a clear peak at z ≃ 2 and a fast rise at z > 2 of the SFRD is compelling for models of galaxy formation. This peak is mainly produced by bright galaxies (L >~ L☉ z=2), requiring that significant gas reservoirs still exist at this epoch and are probably replenished by cold accretion and wet mergers, while feedback or quenching processes are not yet strong enough to lower the SF. The dust attenuation maximum is reached ~2 Gyr after the SFRD peak, implying a contribution from the intermediate-mass stars to the dust production at z < 2. [ABSTRACT FROM AUTHOR]

Capacitance-voltage (C-V) measurements are used to determine the effect of vacuum ultraviolet (VUV) and ultraviolet irradiation on mobile charges in porous low-k organosilicate (SiCOH) dielectrics. Hysteresis in the C-V characteristics shows that VUV irradiation increases the number of mobile charges in the dielectric. This is because VUV photons excite the trapped electrons from defect states to make them mobile carriers. Conversely UV reverses this effect by reducing the mobile charges through photoemission of free electrons and repopulation of trap states. Thus UV irradiation can be used to improve the electrical properties of plasma-processed dielectrics that are subjected to VUV irradiation. [ABSTRACT FROM AUTHOR]

We have developed intense vacuum ultraviolet (VUV) radiation sources for advanced material processing, such as photochemical surface reactions and precise processing on a nanometer scale. We have constructed a new VUV laser system to generate sub-picosecond pulses at the wavelength of 126 nm. A seed VUV pulse was generated in Xe as the 7th harmonic of a 882-nm Ti:sapphire laser. The optimum conversion was achieved at the pressure of 1.2 Torr. The seed pulse will be amplified by the $\mathrm{Ar}_{2}^{*}$ media generated by an optical-field-induced ionization Ar plasma produced by the Ti:sapphire laser. We have obtained a gain coefficient of g=0.16 cm. Our developing system will provide VUV ultra-short pulses with sub-μJ energy at a repetition rate of 1 kHz. [ABSTRACT FROM AUTHOR]

The open-closed magnetic field line boundary (OCB) delimits the region of open magnetic flux forming the polar cap in the Earth's ionosphere. We present a reliable, automated method for determining the location of the poleward auroral luminosity boundary (PALB) from far ultraviolet (FUV) images of the aurora, which we use as a proxy for the OCB. This technique models latitudinal profiles of auroral luminosity as both a single and double Gaussian function with a quadratic background to produce estimates of the PALB without prior knowledge of the level of auroral activity or of the presence of bifurcation in the auroral oval. We have applied this technique to FUV images recorded by the IMAGE satellite from May 2000 until August 2002 to produce a database of over a million PALB location estimates, which is freely available to download. From this database, we assess and illustrate the accuracy and reliability of this technique during varying geomagnetic conditions. We find that up to 35% of our PALB estimates are made from double Gaussian fits to latitudinal intensity profiles, in preference to single Gaussian fits, in nightside magnetic local time (MLT) sectors. The accuracy of our PALBs as a proxy for the location of the OCB is evaluated by comparison with particle precipitation boundary (PPB) proxies from the DMSP satellites. We demonstrate the value of this technique in estimating the total rate of magnetic reconnection from the time variation of the polar cap area calculated from our OCB estimates. [ABSTRACT FROM AUTHOR]

Luminescence emission and excitation spectra as well as decay kinetics of Y2O3-Yb nanoparticles elaborated by the polyol mediated synthesis method have been measured at liquid helium temperature under VUV excitation. In nanoparticles the ratio of intensities of Charge Transfer Luminescence (CTL) and exciton excitation peaks differs from that for Y2O3-Yb single crystal, and changes with the particle size variation from 13 to 52 nm. This effect can be connected with the variation of excitation light scattering with particle dimensions. Two types of luminescence decay acceleration are observed. Acceleration of exponential decay time with decrease of nanoparticle size and the appearance of very fast decay component in small nanoparticles that we connected to energy transfer to the surface defects. [ABSTRACT FROM AUTHOR]

Doubly doped LaF3:Er, Nd scintillation crystals were grown by modified micropulling-down method. The Er codoping was chosen to enhance the energy transfer from the host lattice to the Nd3+ luminescence center via the 5d-levels of Er3+, which can be enabled by the overlap of Er3+ 5d-4f emission spectrum with the Nd3+ 4f-5d absorption. However, no relevant energy transfer was found by photo- and radioluminescence spectra measurements. The reasons of no significant positive effect of Er codoping are discussed. [ABSTRACT FROM AUTHOR]

Because there is an overlap of the 5d-4f emission transition of Tm3+ and absorption transition of Nd3+, an energy transfer between Nd3+ and Tm3+ in LaF3 was supposed to enhance the efficiency of the previously studied Nd:LaF3 scintillation material. In this study, 0.1% and 1%Tm, Nd, and Tm, Nd codoped LaF3 single crystals scintillators were developed using micro-pulling down method (µ-PD), and their optical properties in the vacuum ultraviolet (VUV) region were evaluated. Tm3+ codopant did not show positive contribution to VUV emission, but energy transfer between Nd3+ and Tm3+ cannot be excluded, although the photoluminescence spectra point just to a competition for energy between the two ions. Gamma-ray response was also measured using the pulse-height distribution measurement. [ABSTRACT FROM AUTHOR]

Upon excitation of natural gas by a capacitive electrodeless discharge, an intense excitation of the (4+) band system of CO in the region of 150-200 nm was observed. Excited CO molecules are accumulated as a result of plasmochemical reactions in the gas-discharge plasma. At a pressure of 15 Torr, a pulse repletion frequency of 100 kHz, and a specific excitation power of ~300 mW/cm3, the power density of radiation of the (4+) band system of CO from the external surface of a radiator was ~5 mW/cm2 at an efficiency of up to ~2%. [ABSTRACT FROM AUTHOR]

Absorption spectroscopy in the vacuum ultraviolet (VUV) domain was performed on the hydrogen-deuteride molecule with a novel Fourier-transform spectrometer based upon wavefront division interferometry. This unique instrument, which is a permanent endstation of the undulator-based beamline DESIRS on the synchrotron SOLEIL facility, opens the way to Fourier-transform spectroscopy in the VUV range. The HD spectral lines in the Lyman and Werner bands were recorded in the 87-112 nm range from a quasi-static gas sample in a windowless configuration and with a Doppler-limited resolution. Line positions of some 268 transitions in the [image omitted] Lyman bands and 141 transitions in the [image omitted] Werner bands were deduced with uncertainties of 0.04 cm-1 (1σ) which correspond to Δλ/λ ∼ 4 × 10-7. This extensive laboratory database is of relevance for comparison with astronomical observations of H2 and HD spectra from highly redshifted objects, with the goal of extracting a possible variation of the proton-to-electron mass ratio (μ = mp/me) on a cosmological time scale. For this reason also calculations of the so-called sensitivity coefficients Ki were performed in order to allow for deducing constraints on Δμ/μ. The Ki coefficients, associated with the line shift that each spectral line undergoes as a result of a varying value for μ, were derived from calculations as a function of μ solving the Schrodinger equation using ab initio potentials. [ABSTRACT FROM AUTHOR]

Abstract-The characteristic properties of microscale capillary plasma electrode structures were experimentally investigated and compared to the dielectric barrier discharge (DBD) structure. The vacuum ultraviolet (VUV) emission from the capillary plasma electrode discharges (CPEDs) was more intense and more efficient than the one from the DBD. Based on VUV emission characteristics, it is confirmed that the CPED-based plasma display could be a possible candidate to find the breakthrough in the luminance and luminous efficiency of plasma display. [ABSTRACT FROM AUTHOR]

The vacuum ultraviolet (VUV) absorption spectrum of difluoromethane (CH2F2) was studied using synchrotron radiation from the storage ring Indus-1, Indore, India. Spectra were recorded in the spectral region 1050-1500 Å (∼8.3-11.8 eV) at a resolution of 1.5 Å. Three absorption band systems were observed in this region. Overall features observed are in good agreement with previously published work. Some discrepancies in assignments of the observed vibronic bands carried out by previous workers have been resolved. The observed bands have been classified in terms of Rydberg series. [ABSTRACT FROM AUTHOR]

The current characteristics of barrier discharges in inert gases (Xe, Kr, and Ar) are compared. It is shown that the shape of the current curve (the number of peaks and their amplitudes) depends on the kind of gas (breakdown voltage) and the frequency of the sinusoidal supply voltage; as the frequency of the voltage decreases, the number of breakdowns tends to increase. It is found that, under the experimental conditions ( P = 300 Torr, d = 4 mm), the amplitude of the discharge current in Xe is two to three times higher, its time is tenfold shorter, and the diameter of the discharge channel is five to ten times smaller compared to other inert gases. These differences can be explained by a considerable difference of the transfer coefficients in Xe from those in Ar and Kr. [ABSTRACT FROM AUTHOR]

Low-pressure premixed laminar n-heptane+propane/oxygenlnitrogen flames were investigated with tunable synchrotron vacuum ultraviolet (VUV) photoionization and molecular-beam sampling mass spectrometry. Three flames with different mass percentage of propane in the fuel blends of 0%, 10%, and 20% were studied. The combustion intermediates were identified by comparing the measured IEs with those values in literatures. Mole fraction profiles of the main species were compared among the three flames. The experimental results provide detailed data in understanding the combustion of n-heptane and n-heptane/propane blends in engine. They are also helpful in establishing and verifying the kinetic models. [ABSTRACT FROM AUTHOR]

Modification and functionalization of polymer surface properties is desired in numerous applications, and a standard technique is a treatment with non-equilibrium gaseous plasma. Fluorinated polymers exhibit specific properties and are regarded as difficult to functionalize with polar functional groups. Plasma methods for functionalization of polyvinylidene fluoride (PVDF) are reviewed and different mechanisms involved in the surface modification are presented and explained by the interaction of various reactive species and far ultraviolet radiation. Most authors used argon plasma but reported various results. The discrepancy between the reported results is explained by peculiarities of the experimental systems and illustrated by three mechanisms. More versatile reaction mechanisms were reported by authors who used oxygen plasma for surface modification of PVDF, while plasma sustained in other gases was rarely used. The results reported by various authors are analyzed, and correlations are drawn where feasible. The processing parameters reported by different authors were the gas pressure and purity, the discharge configuration and power, while the surface finish was predominantly determined by X-ray photoelectron spectroscopy (XPS) and static water contact angle (WCA). A reasonably good correlation was found between the surface wettability as probed by WCA and the oxygen concentration as probed by XPS, but there is hardly any correlation between the discharge parameters and the wettability. [ABSTRACT FROM AUTHOR]

Laminar premixed stoichiometric methane/hydrogen/oxygen/argon flames were investigated with tun- able synchrotron vacuum ultraviolet (VUV) photoionization and molecular-beam sampling mass spectrometry techniques. The methane/hydrogen fuel blends with hydrogen volumetric fraction of 0, 20%, 40%, 60% and 80% were studied. All observed flame species, including stable intermediates and radicals in the flames, were detected by measuring photoionization mass spectra and photoionization efficiency (PIE) spectra. Mole fraction profiles of major species and intermediates were derived by scanning burner at some selected photon energies near ionization thresholds. The influence of hydrogen addition on mole fraction of major species and intermediates was analyzed. The results show that the major species mole fraction of CO1 CO2 and CH4 decreases with the increase of hydrogen fraction. The mole fraction of intermediates measured in this experiment decreases remarkably with the increase of hydrogen fraction. This would be due to the increase of H and OH radicals by hydrogen addition and the high diffusivity and activity of H radical promoting the chemical reaction. In addition, the increase of H/C ratio with the increase of hydrogen fraction also leads to the decrease of the mole fraction of carbon-related intermediates and contributes to the decrease of unburned and incomplete combustion products. [ABSTRACT FROM AUTHOR]

The efficiency of a coherent vacuum ultraviolet (VUV) source at 125 nm, based on two-photon resonant four-wave mixing in mercury vapor, has been enhanced by up to two orders of magnitude. This enhancement was obtained by locally heating a liquid mercury surface with a pulsed excimer laser, resulting in a high-density vapor plume in which the nonlinear interaction occurred. Energies up to 5 μJ (1 kW peak power) have been achieved while keeping the overall mercury cell at room temperature, avoiding the use of a complex heat pipe. We have observed a strong saturation of the VUV yield when peak power densities of the fundamental beams exceeded the GW/cm2 range, as well as a large intensity-dependent broadening (up to ∼ 30 cm-1) of the two-photon resonance. The source has potential applications for high-resolution interference lithography and photochemistry. [ABSTRACT FROM AUTHOR]

A series of phosphors Ca3La3(1-x)Tb3x(BO3)5 were synthesized by using a high-temperature solid-state reaction technique, and their VUV-vis luminescence properties were investigated. Strong host-related absorption is observed in the VUV region, and the f–d transitions of Tb3+ in the host lattice are assigned and discussed. The influence of both the doping concentration and the temperature on the spectroscopic properties that include the relative emission intensity and the decay time is investigated. [ABSTRACT FROM AUTHOR]

Treatment of poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) with vacuum ultraviolet (VUV) radiation from high pressures of helium in rotating dc arc plasmas was investigated. X-ray photoelectron spectroscopy (XPS) detected defluorination and appearance of the functional groups (C=O, O–C=O and C–O) on the surface. Fourier transform infrared (FT-IR) spectroscopy showed the appearance of a band at 1884 cm-1 indicating the formation of the carboxylic acid fluoride moiety, –(C=O)–F. Improvement in film wettability was observed by contact angle measurements while SEM micrographs showed an increased amount of cracking on the surface with VUV exposure. Adhesion measurements of Cu sputter-coated onto the photo-modified surfaces resulted in failure within the fluoropolymer (cohesive failure) and not at the Cu-fluoropolymer interface. Cohesive failure occurred with shorter treatment times than for VUV exposure downstream from low pressure Ar microwave plasmas. [ABSTRACT FROM AUTHOR]

Laser plasma interaction experiments have been performed using an fs Titanium Sapphire laser. Plasmas have been generated from planar PMMA targets using single laser pulses with 3.3 mJ pulse energy, 50 fs pulse duration at 800 nm wavelength. The electron density distributions of the plasmas in different delay times have been characterized by means of Nomarski Interferometry. Experimental data were compared with hydrodynamic simulation. First results to characterize the plasma density and temperature as a function of space and time are obtained. This work aims to generate plasmas in the warm dense matter (WDM) regime at near solid-density in an ultra-fast laser target interaction process. Plasmas under these conditions can serve as targets to develop X-ray Thomson scattering as a plasma diagnostic tool, e.g., using the Vacuum ultraviolet (VUV) free-electron laser (FLASH) at Dentsches Elektronen-Synchrotron (DESY) Hamburg. [ABSTRACT FROM AUTHOR]

A theory is presented of the generation of low-frequency transition radiation by a short laser pulse at a plasma-vacuum interface. The wave electromagnetic fields are excited by the vortex electric current that is generated at the plasma boundary by the ponderomotive force of the laser field. The spectral, angular, and energy parameters of the transition radiation, as well as the spatiotemporal structure of the emitted waves in vacuum and in plasma, are investigated. It is shown that the parameters of the transition radiation depend essentially on the ratio of the laser pulse duration to the plasma oscillation period. Under conditions typical of present-day laser-plasma experiments, the transition electromagnetic radiation is generated in the terahertz frequency range and its power can reach several megawatts. [ABSTRACT FROM AUTHOR]

We investigated the effect of Xe content variation on the luminous efficiency of two different subpixel types, i.e., segmented electrode in delta color arrayed, enclosed subpixel (SDE) and conventional stripe barrier type, in an alternating current plasma display panel through three-dimensional (3-D) numerical simulations. The simulation result agreed well with the experimental result where the SDE structure showed to have higher luminous efficiency improvement with increasing Xe content than the conventional structure did. The conventional cell type was found to have higher vacuum ultraviolet (VUV) generation efficiency at low Xe content as compared with SDE structure, but as the Xe content increased, the SDE type showed a higher improvement in efficiency due to the lower plasma loss to the enclosing surfaces. Using the ray-optics code in conjunction with the 3-D plasma simulation, the transport efficiency of visible light from phosphor through the front plate in the SDE structure, which has a higher aperture ratio, was higher than that of the conventional structure with much increased improvement with the increase of Xe content. [ABSTRACT FROM AUTHOR]

Processes of cluster formation in a supersonic argon-krypton jet at low concentrations of the krypton impurity (down to 1×10-3%) are investigated by a luminescence method. VUV diagnostics of the picture of heterogeneous nucleation, including its earliest stages, is employed for the first time. Attention is focused mainly on the behavior of the emission bands belonging to the neutral excimers Ar2* and Kr2* and the charged homoatomic complexes (Ar4+)* and (Kr4+)* and the heteroatomic exciplexes (Ar/Kr)*. In the first stage of heterogeneous nucleation the nuclei can be krypton atoms (dimers). Beginning at krypton concentrations in the gas mixture of 0.02% and higher a multiatomic krypton core is formed in the cluster. When such clusters are ionized the ion is located in the krypton core, and its electric field has a substantial influence on the parameters of the emission band of an Ar/Kr molecule found at the argon/krypton boundary. The results of this study demonstrate the high efficiency of VUV spectroscopy for studying processes of heteroatomic cluster formation in supersonic jets. [ABSTRACT FROM AUTHOR]

A methanol actinometer is used for measuring the intensity of vacuum UV radiation of a Xe excilamp. The absorbed radiation dose is determined by measuring the concentration of formaldehyde, which is the decay product of methanol illuminated by UV radiation, with the use of amperometric titration. [ABSTRACT FROM AUTHOR]

Multichannel surface discharges possess a number of advantageous characteristics for the optical pumping of photochemically driven lasers. This work reports on a type of large-area low-inductance sources of intense UV-VUV (vacuum-ultraviolet) radiation based on spatially stabilized multichannel discharges in gases. The discharges consist of several dozens of closely located parallel plasma channels initiated synchronously along a dielectric surface on the area of several hundred square centimeters. In comparison with a large-area diffuse surface discharge, the plasma confinement within relatively thin channels greatly improves the efficiency of the discharge emission in the VUV spectral range. Several techniques are introduced, which allow a synchronous formation and homogeneous development of multiple spatially stabilized discharge channels. Technical efficiency of the discharge radiation within the spectral range of 120–200 nm reaches 5% and an effective brightness temperature of the radiating plasma exceeds 20 kK. Synchronous operation of a number of multichannel discharge modules producing high-intensity submicrosecond optical pulses is demonstrated, which is of importance for the pump source scaling and geometrical adaptation. [ABSTRACT FROM AUTHOR]

We have studied the action of pulsed vacuum ultraviolet (VUV) radiation of an ArF excimer laser (wavelength, 193 nm; pulse duration, 20 ns; pulse energy density, 40–50 J/cm2) on thin amorphous films of titanium oxide (TiO2) grown by light-assisted molecular beam epitaxy. A comparison of the Raman spectra of samples measured before and after exposure shows that VUV irradiation at increasing fluence induces the crystallization of amorphous TiO2 to anatase, which is further transformed into rutile. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]