A high-power laser transmitter for ground-based and airborne water-vapor measurements in the troposphere

A gain-switched high-power single-frequency Ti:sapphire laser was developed. It is pumped with a frequency-doubled diode-pumped Nd:YAG laser. The laser fulfills the requirements for a transmitter of a water-vapor differential absorption lidar (DIAL), intended for accurate high temporally- and spatially-resolved measurements from the ground to the upper troposphere. The laser was developed using thermal, resonator-design, spectral, and pulse-evolution models. There were layouts assembled for operation at 935 nm and 820 nm optimized for airborne and groundbased measurements, respectively. A birefringent filter and an external-cavity diode laser as an injection seeder are controlling the spectral properties of the transmitter. With a frequency stability of 99.7 %, the total error from the laser properties is smaller than 5 % for water-vapor measurements in the troposphere. The laser beam profile is near-Gaussian with M2 < 2. The achieved laser power was 4.5 W at 935 nm and 7 W at 820 nm at repetition rate of 250 Hz. These values are the highest reported for a single-frequency Ti:sapphire laser. As a part of a ground-based water-vapor DIAL system, the transmitter was deployed during the measurement campaign COPS (Convective and Orographically-induces Precipitation Study). Comparisons with radiosondes confirmed a high precision of the acquired water-vapor day- and nighttime measurements.Ein verstärkungsgeschalter leistungsstarker monofrequenter Ti:Saphir-Laser, der mit einem frequenzverdoppeltem diodengepumpten Nd:YAG Laser gepumpt ist, wurde entwickelt. Der Laser erfüllt die hohen Anforderungen eines Transmitters für ein Wasserdampf-Differential-Absorption-Lidar (DIAL), der mit hoher zeitlicher und räumlicher Auflösung Messungen innerhalb der Troposphäre durchführen soll. Für die Entwicklung des Lasers wurden Modelle für die thermischen Eigenschaften, das Resonatordesign, das Emissionspektrum sowie den Pulsaufbau verwendet. Es wurden Laseraufbauten gefertigt, die für den Einsatz bei 935 nm für Flugzeug-Plattformen bzw. 820 nm für bodengestützte Messungen optimiert sind. Ein doppelbrechender Filter und ein External-Cavity-Diodenlaser als Injection-seeder sorgen für die hohe Güte der spektralen Eigenschaften des Senders. Mit einer Frequenzstabilität 99,7 % ist der Gesamtfehler der Wasserdampfmessungen in der Troposphäre, der durch die Eigenschaften des Lasers bedingt ist, kleiner als 5 %. Werte der mittleren Ausgangsleistung von 4,5 W bei 935 nm und 7 W bei 820 nm sind die zur Zeit höchsten, die von einem monofrequenten Ti:Saphir-Laser mit nahezu gaussförmigem Strahlprofil und M2 < 2 erreicht wurden. Als Teil eines bodengestützten Wasserdampf DIALs, wurde der Transmitter während der Messkampagne COPS (Convective and Orographically-induces Precipitation Study) verwendet. Vergleiche von Messungen bei Tag und bei Nacht mit Radiosondenaufstiegen zeigten gute Übereinstimmungen

Students’ educational experiences and interaction with residents on night shifts

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/137686/1/tct12561.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/137686/2/tct12561_am.pd

Magnetism and morphology of Co nanocluster superlattices on GdAu2 /Au(111)- (13×13)

Under the terms of the Creative Commons Attribution License 3.0 (CC-BY).-- et al.We present a comprehensive study of the magnetism and morphology of an ultrahigh density array of Co nanoclusters self-assembled on the single atomic layer GdAu2 on Au(111) template surface. Combining scanning tunneling microscopy, x-ray magnetic circular dichroism, and magneto-optical Kerr effect measurements, we reveal a significant enhancement of the perpendicular magnetic anisotropy energy for noncoalesced single atomic layer nanoclusters compared to Co/Au(111). For coverages well beyond the onset of coalescence, we observe room-temperature in-plane magnetic remanence.We acknowledge funding from the Swiss National Science Foundation, from the Sino-Swiss Science and Technology Cooperation Project No. IZLCZ2 123892, from the Spanish Ministerio de Ciencia e Innovacion (MAT2010-21156-C03-03), from the Gipuzkoako Foru Aldundia, from the European Social Fund within the program JAE-Doc, the Basque Government (IT-621-13 and IT-627-13) and SAIOTEK (S-PE12UN095), as well as from the EU Calipso program for synchrotron access funding. The MBE chamber on DEIMOS was funded by the Agence National de la Recherche with Grant No. ANR-05-NANO-073.Peer Reviewe

Electronic structure of titanylphthalocyanine layers on Ag(111)

We have investigated the electronic structures of axially oxo functionalized titanylphthalocyanine (TiOPc) on Ag(111) by X-ray and ultraviolet photoelectron spectroscopies, two-photon photoemission, X-ray absorption spectroscopy, and X-ray magnetic circular dichroism. Furthermore, we use complementary data of TiOPc on graphite and planar copper phthalocyanine (CuPc) on Ag(111) for a comparative analysis. Both molecules adsorb on Ag(111) in a parallel orientation to the surface, for TiOPc with an oxygen-up configuration. The interaction of nitrogen and carbon atoms with the substrate is similar for both molecules, while the bonding of the titanium atom to Ag(111) in the monolayer is found to be slightly more pronounced than in the CuPc case. Ultraviolet photoemission spectroscopy reveals an occupation of the lowest unoccupied molecular orbital (LUMO) level in monolayer thick TiOPc on Ag(111) related to the interaction of the molecules and the silver substrate. This molecule-metal interaction also causes an upward shift of the Ag(111) Shockley state that is transformed into an unoccupied interface state with energies of 0.23 and 0.33 eV for the TiOPc monolayer and bilayer, respectively, at the Brillouin zone center.The authors acknowledge financial support from the Deutsche Forschungsgemeinschaft through SFB 1083 “Structure and Dynamics of Internal Interfaces”, the Spanish CSIC I-Link programm, the Spanish Ministry of Economy and Competitiveness, MINECO (under Contract No. MAT2016-78293-C6-2-R, and Severo Ochoa No. SEV-2013-0295.), and by the Secretariat for Universities and Research, Knowledge Department of the Generalitat de Catalunya (2014 SGR 715). M. Paradinas thanks the Spanish Government for financial support through PTA2014-09788-I fellowships. ICN2 is funded by the CERCA Programme/Generalitat de Catalunya.Peer Reviewe

Strain dependent light-off temperature in catalysis revealed by planar laser-induced fluorescence

Understanding how specific atom sites on metal surfaces lower the energy barrier for chemical reactions is vital in catalysis. Studies on simplified model systems have shown that atoms arranged as steps on the surface play an important role in catalytic reactions, but a direct comparison of how the light-off temperature is affected by the atom orientation on the step has not yet been possible due to methodological constraints. Here we report in situ spatially resolved measurements of the CO production over a cylindrical-shaped Pd catalyst and show that the light-off temperature at different parts of the crystal depends on the step orientation of the two types of steps (named A and B). Our finding is supported by density functional theory calculations, revealing that the steps, in contrast to what has been previously reported in the literature, are not directly involved in the reaction onset but have the role of releasing stress.The authors thank the Knut and Alice Wallenberg Foundation, the Swedish Research Council, the Swedish Foundation for Strategic Research, and the Crafoord Foundation. Support by the MAX IV staff is gratefully acknowledged. The calculations were performed at C3SE through a SNIC grant. J.E.O. acknowledges support from the Spanish Ministry of Economy (MAT2013-46593-C6-4-P) and the Basque Government (IT621-13).Peer Reviewe