Abstract: We realized a solid-state-based vacuum ultraviolet frequency comb by harmonics generation in an external enhancement cavity. Optical conversions were so far reported by only using gaseous media. We present a theory that allows the most suited solid generation medium to be selected for specific target harmonics by adapting the material’s bandgap. We experimentally use a thin AlN film grown on a sapphire substrate to realize a compact frequency comb high-harmonic source in the Deep Ultraviolet (DUV)/Vacuum Ultraviolet/Deep Ultraviolet (VUV) spectral range. By extending our earlier VUV source [Opt. Express 26, 21900 (2018)] with the enhancement cavity, a sub-Watt level Ti:sapphire femtosecond frequency comb is enhanced to 24 W stored average power, its 3rd, 5th, and 7th harmonics are generated, and the targeted 5th harmonic’s power at 160 nm increased by two orders of magnitude. The emerging nonlinear effects in the solid medium, together with suitable intra-cavity dispersion management, support optimal enhancement and stable locking. To demonstrate the realized frequency comb’s spectroscopic ability, we report on the beat measurement between the 3rd harmonic beam and a 266 nm CW laser reaching about 1 MHz accuracy. [Link]
J. Seres, E. Seres, C. Serrat, E. C. Young, J. S. Speck, and T. Schumm

Abstract: This work studies the ability of laser-induced breakdown spectroscopy (LIBS) to improve the detection of light elements such as silicon (Si), boron (B), carbon (C), and sulfur (S). In this study, the plasma decay over time was simulated using the LIBS application provided by NIST, obtaining spectra in the spectral range ranging from the vacuum ultraviolet (VUV) to the near infrared (NIR) region. Since the electron density (ne) and plasma temperature (Te) decrease during the decaying process, the intensities of emission lines from neutral, singly ionized, and doubly ionized species were calculated. The results allowed us to determine the range of suitable ne and Te for experimental measurements, and to construct a Saha–Boltzmann (SB) plot using neutral, singly ionized, and doubly ionized species. Samples containing Si, B, C, and S were measured at delays of 100–1000 ns after the laser shot at low pressure (13 mbar) in a helium atmosphere. From the measured data, suitable lines were chosen in the VUV range to calculate the Te of plasma for each sample at different delays. The results demonstrate that due to the inclusion of multiple species across VUV–UV–NIR, an appreciable improvement in the accuracy of Te was obtained, which is an essential factor for calibration-free LIBS (CF-LIBS).. [Link]
Pavel Veis, Alicia Marín-Roldán and Jaroslav Krištof

Abstract: Time- and angle-resolved photoemission spectroscopy (trARPES) employing a 500 kHz extreme-ultraviolet light source operating at 21.7 eV probe photon energy is reported. Based on a high-power ytterbium laser, optical parametric chirped pulse amplification, and ultraviolet-driven high-harmonic generation, the light source produces an isolated high-harmonic with 110 meV bandwidth and a flux of more than 1011 photons/s on the sample. Combined with a state-of-the-art ARPES chamber, this table-top experiment allows high-repetition rate pump-probe experiments of electron dynamics in occupied and normally unoccupied (excited) states in the entire Brillouin zone and with a temporal system response function below 40 fs. [Link]
M. Puppin, Y. Deng, C. W. Nicholson, J. Feldl, N. B. M. Schröter, H. Vita, P. S. Kirchmann, C. Monney, L. Rettig, M. Wolf, and R. Ernstorfer

Abstract: Time- and angle-resolved photoelectron spectroscopy (trARPES) is a powerful method to track the ultrafast dynamics of quasiparticles and electronic bands in energy and momentum space. We present a setup for trARPES with 22.3 eV extreme-ultraviolet (XUV) femtosecond pulses at 50-kHz repetition rate, which enables fast data acquisition and access to dynamics across momentum space with high sensitivity. The design and operation of the XUV beamline, pump-probe setup, and UHV endstation are described in detail. By characterizing the effect of space-charge broadening, we determine an ultimate source-limited energy resolution of 60 meV, with typically 80-100 meV obtained at 1-2e10 photons/s probe flux on the sample. The instrument capabilities are demonstrated via both equilibrium and time-resolved ARPES studies of transition-metal dichalcogenides. The 50-kHz repetition rate enables sensitive measurements of quasiparticles at low excitation fluences in semiconducting MoSe2, with an instrumental time resolution of 65 fs. Moreover, photo-induced phase transitions can be driven with the available pump fluence, as shown by charge density wave melting in 1T-TiSe2. The high repetition-rate setup thus provides a versatile platform for sensitive XUV trARPES, from quenching of electronic phases down to the perturbative limit.
Jan Heye Buss, He Wang, Yiming Xu, Julian Maklar, Frederic Joucken, Lingkun Zeng, Sebastian Stoll, Chris Jozwiak, John Pepper, Yi-De Chuang, Jonathan D. Denlinger, Zahid Hussain, Alessandra Lanzara, Robert A. Kaindl

Abstract: Read at NATURE website A structurally simple dielectric barrier discharge based mercury-free plasma UV-light source has been developed for efficient water disinfection. The source comprises of a dielectric barrier discharge arrangement between two co-axial quartz tubes with an optimized gas gap. The outer electrode is an aluminium baked foil tape arranged in a helical form with optimized pitch, while the inner electrode is a hollow aluminium metallic rod, hermetically sealed. Strong bands peaking at wavelengths 172 nm and 253 nm, along with a weak band peaking at wavelength 265 nm have been simultaneously observed due to plasma radiation from the admixture of xenon and iodine gases. The developed UV source has been used for bacterial deactivation studies using an experimental setup that is an equivalent of the conventional house-hold water purifier system. Deactivation studies for five types of bacteria, i.e., E. coli, Shigella boydii, Vibrio, Coliforms and Fecal coliform have been demonstrated with 4 log reductions in less than ten seconds.
Ram Prakash, Afaque M. Hossain, U. N. Pal, N. Kumar, K. Khairnar & M. Krishna Mohan

Abstract: Application of multilayer technology is extended to high extinction coefficient materials, which is introduced into metal-dielectric filter design. Metal materials often have high extinction coefficients in far ultraviolet (FUV) region, so optical thickness of metal materials should be smaller than that of the dielectric material. A broadband FUV filter of 9-layer non-periodic Al/MgF2 multilayer was successfully designed and fabricated and it shows high reflectance in 140-180 nm, suppressed reflectance in 120-137 nm and 181-220 nm
Xiao-Dong Wang, Bo Chen, Hai-Feng Wang, Fei He, Xin Zheng, Ling-Ping He, Bin Chen, Shi-Jie Liu, Zhong-Xu Cui, Xiao-Hu Yang and Yun-Peng Li

Abstract: The photoinduced room-temperature-stable increase in the refractive index by ~5x10E4 at a wavelength of 1.55um was observed in phosphosilicate fibers without their preliminary loading with molecular hydrogen. It is shown that irradiation of preliminary hydrogen-loaded fibers by an ArF laser at 193 nm enhances the efficiency of refractive-index induction by an order of magnitude. The induced-absorption spectra of preforms with a phosphosilicate glass core and optical fibers fabricated from them are studied in a broad spectral range from 150 to 5000 nm. The intense induced-absorption band (~800 cm-1) at 180 nm is found, which strongly affects the formation of the induced refractive index. The quantum-chemical model of a defect related to this band is proposed.
A.A. Rybaltovsky, V.O. Sokolov, V.G. Plotnichenko, A.V. Lanin, S.L. Semenov, A.N. Gur'yanov, V.F. Khopin, E.M. Dianov

Abstract: The performance of cesium iodide as a reflective photocathode is presented. The absolute quantum efficiency of a 500nm thick film of cesium iodide has been measured in the wavelength range 150nm-200nm. The optical absorbance has been analyzed in the wavelength range 190nm-900nm and the optical and gap energy has been calculated. The dispersion properties were determined from the refractive index using an envelope plot of the transmittance data. The morphological and elemental film composition have been investigated by atomic force microscopy and X-ray photo-electron spectroscopy techniques.
Triloki, R. Rai, Nikita Gupta, Nabeel F.A. Jammal, B.K. Singh

Abstract: We demonstrated efficient generation of ultrafast extreme ultraviolet (XUV) pulses at 89 nm from an intense 267 nm UV femtosecond filamentation in argon gas. The XUV pulse generation efficiency was significantly enhanced through UV filament termination from the argon gas into the background vacuum that prevented backconversion of the generated third-harmonic XUV to the fundamental-wave UV pulses. This was further combined with noncollinear UV filament interaction that produced volume-plasma to pre-extract XUV pulses from the filament core, resulting in further XUV enhancement. The generated 89 nm XUV pulses reached what is so far, to our knowledge, the highest pulse energy of 190 nJ
Wang D, Li W, Ding L, Zeng H

Abstract: A large number of current and future experiments in neutrino and dark matter detection use the scintillation light from noble elements as a mechanism for measuring energy deposition. The scintillation light from these elements is produced in the extreme ultraviolet (EUV) range, from 60 - 200 nm. Currently, the most practical technique for observing light at these wavelengths is to surround the scintillation volume with a thin film of Tetraphenyl Butadiene (TPB) to act as a fluor. The TPB film absorbs EUV photons and reemits visible photons, detectable with a variety of commercial photosensors. Here we present a measurement of the re-emission spectrum of TPB films when illuminated with 128, 160, 175, and 250 nm light. We also measure the fluorescence efficiency as a function of incident wavelength from 120 to 250 nm.
V. M. Gehman, S. R. Seibert, K. Rielage, A. Hime, Y. Sun, D.-M. Mei, J. Maassen, D. Moore

Abstract: We report on the photoemission properties of 300 Å thick transmissive- and 5000 Å thick reflective UV-sensitive CsBr photocathodes. Following post-evaporation heat treatment at 70°C the absolute quantum efficiency is 35% at 150 nm, with a red boundary cut-off at about 195 nm. Extensive aging studies of CsBr and CsI photocathodes, under high photon flux and under ion bombardment in gas avalanche multiplication mode, were carried out for the first time without exposure to air. The results are compared with the previously published data on CsI aging and the methodology of the aging tests is discussed in details.
B. K. Singh, E. Shefer, A. Breskin, R. Chechik and N. Avraham

Abstract: We demonstrate compression of ultrashort light pulses in the ultraviolet (UV) by impulsively excited molecular wave-packets in nitrogen filled in a 25 cm long hollow waveguide of 128 µm diameter. After compression with CaF2 prisms the pulse duration was determined by XFROG to be 23 fs with a time-bandwidth product of 0.50. The advantages of our technique are high efficiency and the possibility to use it also for pulses at wavelength shorter than 200 nm. The experimental observations are explained by a theoretical model.
Noack, F.; Steinkellner, O.; Tzankov, P.; Ritze, H.-H.; Herrmann, J.; Kida, Y.

Abstract: Recent fluorescence studies suggest that ultrashort pulse laser excitation may be highly selective. Selective high-intensity laser excitation holds important consequences for the physics of multiphoton processes. To establish the extent of this selectivity, we performed a detailed comparative study of the vacuum ultraviolet fluorescence resulting from the interaction of N2 and Ar with high-intensity infrared ultrashort laser pulses. Both N2 and Ar reveal two classes of transitions, inner-valence ns←np and Rydberg np←n'l'. From their pressure dependence, we associate each transition with either plasma or direct laser excitation. Furthermore, we qualitatively confirm such associations with the time dependence of the fluorescence signal. Remarkably, only N2 presents evidence of direct laser excitation. This direct excitation produces ionic nitrogen fragments with inner-valence (2s) holes, two unidentified transitions, and one molecular transition, the N+2 :X 2∑+g←C 2∑+u . We discuss these results in the light of a recently proposed model for multiphoton excitation.
Coffee, Ryan N. and Gibson, George N.

Abstract: We develop and implement an experimental strategy for the generation of high-energy high-order harmonics (HHG) in gases for studies of nonlinear processes in the soft x-ray region. We generate high-order harmonics by focusing a high energy Ti:Sapphire laser into a gas cell filled with argon or neon. The energy per pulse is optimized by an automated control of the multiple parameters that influence the generation process. This optimization procedure allows us to obtain energies per pulse and harmonic order as high as 200 nJ in argon and 20 nJ in neon, with good spatial properties, using a loose focusing geometry (f#≈400) and a 20 mm long medium. We also theoretically examine the macroscopic conditions for absorption-limited conversion efficiency and optimization of the HHG pulse energy for high-energy laser systems
Rudawski P, Heyl CM, Brizuela F, Schwenke J, Persson A, Mansten E, Rakowski R, Rading L, Campi F, Kim B, Johnsson P, L'huillier A.

Abstract: The Southwest Research Institute Ultraviolet Reflectance Chamber (SwURC) is a highly capable UV reflectometer chamber and data acquisition system designed to provide bidirectional scattering data of various surfaces and materials. The chamber provides laboratory-based UV reflectance measurements of water frost/ice, lunar soils, simulants, and analogs to support interpretation of UV reflectance data from the Lyman Alpha Mapping Project (LAMP) Lunar Reconnaissance Orbiter (LRO). A deuterium lamp illuminates a monochromator with a nominal wavelength range of 115 nm to 210 nm. The detector scans emission angles -85° to +85°in the principal plane. Liquid nitrogen passed through the sample mount enables constant refrigeration of tray temperatures down to 78 K to form water ice and other volatile samples. The SwURC can be configured to examine a wide range of samples and materials through the use of custom removable sample trays, connectors, and holders. Calibration reference standard measurements reported here include Al/MgF2 coated mirrors for specular reflection and Fluorilon for diffuse reflectances. This calibration work is a precursor to reports of experiments measuring the far-UV reflectance of water frost, lunar simulants, and Apollo soil sample 10084 in support of LRO-LAMP.
Proc. SPIE 8859, UV, X-Ray, and Gamma-Ray Space Instrumentation for Astronomy XVIII, 88590R (September 26, 2013); doi:10.1117/12.2024460
Preston L. Karnes ; Kurt D. Retherford ; Gregory S. Winters ; Eric C. Bassett ; Stephen M. Escobedo ; Edward L. Patrick ; Amanda Richter ; Michael W. Davis ; Paul F. Miles ; Joel W. Parker ; G. Randall Gladstone ; Thomas K. Greathouse ; Eric R. Schindhelm ; Lori M. Feaga ; S. Alan Stern

Abstract: We study thorium-doped CaF2 crystals as a possible platform for optical spectroscopy of the 229Th nuclear isomer transition. We anticipate two major sources of background signal that might cover the nuclear spectroscopy signal: VUV-photoluminescence, caused by the probe light, and radioluminescence, caused by the radioactive decay of 229Th and its daughters. We find a rich photoluminescence spectrum at wavelengths above 260 nm, and radioluminescence emission above 220 nm. This is very promising, as fluorescence originating from the isomer transition, predicted at a wavelength shorter than 200 nm, could be filtered spectrally from the crystal luminescence. Furthermore, we investigate the temperature-dependent decay time of the luminescence, as well as thermoluminescence properties. Our findings allow for an immediate optimization of spectroscopy protocols for both the initial search for the nuclear transition using synchrotron radiation, as well as future optical clock operation with narrow-linewidth lasers.
Simon Stellmer, Matthias Schreitl, and Thorsten Schumm

Abstract: Read at NATURE website Novel table-top sources of extreme ultraviolet (XUV) light based on high-harmonic generation (HHG) yield unique insight into the fundamental properties of molecules, nanomaterials, or correlated solids, and enable advanced applications in imaging or metrology. Extending HHG to high repetition rates portends great experimental benefits, yet efficient XUV conversion of correspondingly weak driving pulses is challenging. Here, we demonstrate a highly-efficient source of femtosecond XUV pulses at 50-kHz repetition rate, utilizing the ultraviolet second-harmonic focused tightly into Kr gas. In this cascaded scheme, a photon flux beyond ≈3×1013 s-1 is generated at 22.3 eV, with 5×10-5 conversion efficiency that surpasses similar directly-driven harmonics by two orders-of-magnitude. This enhancement exceeds the predicted dipole wavelength scaling, evidencing improved phase-matching for ultraviolet-driven HHG under tight focusing as corroborated by simulations. Spectral isolation of a single sub-80 meV harmonic renders this bright, 50-kHz XUV source a powerful tool for ultrafast photoemission, nanoscale imaging and other applications.
He Wang, Yiming Xu, Stefan Ulonska, Predrag Ranitovic, Joseph S. Robinson and Robert A. Kaindl

Abstract: Specialized soft x-ray and vacuum ultraviolet ~VUV! diagnostics used to monitor impurity emissions from fusion plasmas are often placed in a very challenging experimental environment. Detectors in these diagnostics must be simple; mechanically robust; immune to electromagnetic interference, energetic particles, and magnetic fields up to several tesla; ultra-high-vacuum compatible; and able to withstand bakeout temperatures up to 300 °C. The design and the photometric calibration of a detector consisting of a P45 phosphor (Y2O2S:Tb), two incoherent fiber-optic bundles coupled with a vacuum feedthrough fiber-optic faceplate, and a photomultiplier tube (PMT) are reported.We have successfully operated the detectors of this type in novel soft x-ray and VUV diagnostics on several fusion plasma facilities. Measurements of the visible photon throughput of the silica/silica incoherent fiber-optic bundle, and the light loss associated with the coupling of the two fibers with the faceplate are presented. In addition, improved absolute measurements of the conversion efficiency of the P45/PMT photodetector based upon the use of a PMT with a bialkali photocathode instead of a multialkali one are presented for the soft x-ray and VUV range of photon wavelengths. The conversion efficiency is defined as the ratio of the photoelectrons ejected from the photocathode of a visible detector, which are excited by the scintillated photons that are emitted from the phosphor in a solid angle of 2p, to the number of soft x-ray photons incident on the phosphor. Sensitive electronic gain measurements of the PMT using the visible scintillated light from the P45 phosphor are compared with the gain measurements supplied by the manufacturer of the PMT, which were performed with a tungsten filament lamp operated at 2856 K.
V.A.Soukhanovskii, S.P.Regan, M.J.May, M.Finkenthal, and H.W. Moos

Abstract: We propose a simple approach to measure the energy of the few-eV isomeric state in 229Th. To this end, 233U nuclei are doped into VUV-transparent crystals, where they undergo α decay into 229Th, and, with a probability of 2%, populate the isomeric state. These 229mTh nuclei may decay into the nuclear ground state under emission of the sought-after VUV γ ray, whose wavelength can be determined with a spectrometer. Based on measurements of the optical transmission of 238U:CaF2 crystals in the VUV range, we expect a signal at least two orders of magnitude larger compared to current schemes using surface implantation of recoil nuclei. The signal background is dominated by Cherenkov radiation induced by β decays of the thorium decay chain. We estimate that, even if the isomer undergoes radiative de-excitation with a probability of only 0.1%, the VUV γ ray can be detected within a reasonable measurement time.
Simon Stellmer, Matthias Schreitl, Georgy A. Kazakov, Johannes H. Sterba, and Thorsten Schumm (see also nuClock.com)

Abstract: The monitoring of the solar spectral irradiance has important scientific significance and application value. This paper describes the principle, structure and performance of the UV-VUV solar spectrometer. The calibration principle and the calibration method of the spectral irradiance responsiveness are emphatically discussed, based on synchrotron radiation. The spectral irradiance responsiveness calibration of UV-VUV solar spectrometer in the 165 nm–320 nm spectral range is realized under vacuum environment with PTB transfer standard deuterium lamp as standard source. The results of the calibration are achieved, factors affecting the accuracy of the calibration are analyzed. The synthesized uncertainty of the calibration is 5.1%
.Hanshuang Li, Bo Li Shurong Wang, Zhigang Li, Futian Li

Abstract: The lunar surface (and other airless planetary bodies) undergoes space weathering by micrometeorite bombardment and charged particle irradiation. Space weathering produces submicroscopic iron (SMFe) particles that are deposited as either fine-grained rims on mineral grains or as larger particles within agglutinates. As a result of space weathering, visiblenear infrared (Vis-NIR) spectra display an increase in the continuum slope (redden a reduction in albedo (darken), and an attenuation of absorption features. There are also complexities in the manifestation of weathering in lunar spectra that are imposed as a result of Fe particle size; larger Fe particle sizes (<100-3000 nm) only darken, but do not redden the Vis-NIR spectra. Modeling techniques in the Vis-NIR have also advanced with knowledge of this by applying Mie theory to account for the variance in particle size. All of this information is relevant and critical towards interpreting lunar surface maturity and composition in the ultraviolet as well, but has yet to be fully explored in a similar manner to the Vis-NIR. The Lunar Reconnaissance Orbiter (LRO) features two ultraviolet instruments: the Lyman Alpha Mapping Project (LAMP) and the Lunar Reconnaissance Orbiter Camera Wide-Angle Camera (WAC). In order to examine the LRO ultraviolet data sets more effectively, we aim to perform complementary spectroscopy measurements and microscopy of lunar samples and analogs that provided guidance to the visible and near-infrared.
Karen R. Stockstill-Cahill, Joshua T.S. Cahill, Karl A. Hibbitts

Abstract: Ba2Mg(BO3)2 – Ba2Ca(BO3)2 solid-solution doped with Eu3+ has been synthesized by the conventional solid-state reaction. The symmetry is lower for Ba2Ca(BO3)2 (monoclinic) than Ba2Mg(BO3)2 (trigonal). The solid-solution has been prepared by substituting Mg2+ ions in Ba2Mg(BO3)2 (BaMBO) with larger Ca2+ ions in the whole percentage range. Eu3+ enters both Ba and Mg/Ca sites. As a result, the emission spectra and luminescent decay times differ under excitation at 395 nm, and 266 nm and the charge transfer band (CTB) energy is different for luminescence with a maximum at 594 and 616 nm (the 5D0 → 7F1 and 5D0 → 7F2 transition, respectively). Increasing Ca2+ concentration redshifts the higher-lying CTB, while simultaneously blue shifts the lower-lying CTB. For the Ba2Ca(BO3)2 the electric dipole to magnetic dipole ratio of the components of the 5D0 emission is smaller, and the luminescence decay time is longer than for the Ba2Mg(BO3)2 host. The Judd-Ofelt analysis shows that the Ωλ parameters do not change with Ca2+ concentration for Eu3+ at Mg/Ca site while changing significantly for Eu3+ at Ba site.
Bartosz Bondzior, Przemysław J.Dereń

Abstract: Europium-doped double perovskite Ba2MgWO6 (BMW) has been successfully obtained by a conventional high-temperature solid-state method. The Eu3+ ions enter only the Mg2+ sites with Oh symmetry, which causes the unit cell to expand. The emission spectra measured at 8 K consists predominantly of a very intense line at 597 nm corresponding to the 5D0 → 7F1 transition. No lines associated with f-f transitions are present on the excitation spectrum, which consists of a broad band centered at 301 nm, resulting from charge transfer transitions O2−→W6+. The emission decay curve for the sample with 0.1% Eu3+ at 10 K is single-exponential with decay time 4.23 ms.
Natalia Miniajluk, Bartosz Bondzior, Dagmara Stefańska, Przemysław J.Dereń

Abstract: The spectroscopic and structural properties of GdxLa1−xAlO3 nanocrystals doped with praseodymium(III) ions have been investigated. The absorption, excitation, and emission spectra and time decay profiles of the praseodymium(III) ions for different perovskite samples were measured and analyzed. The influence of annealing temperature, as well as the influence of the La/Gd ratio on the samples luminescent properties, were analyzed and discussed.
K. Lemański, B. Bondzior,a D. Szymańskia and P. J. Dereńa

Abstract: Intrinsic properties of optical ceramics of MgAl2O4 have been studied by means of low-temperature cathodo-, photo- and thermo-luminescence methods. Based on the excitation spectra for different emissions measured at 6 K, the UV luminescence at 4.5–5.8 eV is tentatively ascribed to bound excitons (formation energy about 7 eV) near antisite defects (cation in a “wrong” position) and electron-hole recombination in a spinel matrix. The complex UV luminescence band peaked around 5 eV undergoes thermal quenching from 6 to 200 K. The value of energy gap is experimentally estimated as 8.2 eV at 80 K. There is no saturation of the absorption connected with the radiation-induced F-type color centers at the rise of 100-keV proton fluence up to 7 × 1017 cm−2, while such irradiation is accompanied by the drastic suppression of cathodoluminescence, especially in UV spectral region. A further study of the origin of this luminescence attenuation still lies ahead.
Eduard Feldbach, Irina Kudryavtseva, Kenichiro Mizohata, Gatis Prieditis, Jyrki Räisänen, Evgeni Shablonin, Aleksandr Lushchik