Browsing by Author "Rohwer, Erich G."

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    Accurate Laboratory Wavelengths of the A1Π(υ' = 0-5)-X1Σ+(υ'' = 0) Vibronic Bands of 12C17O and 12C18O
    (IOP Science, 2006) Du Plessis, Anton; Rohwer, Erich G.; Steenkamp, Christine M.
    Twenty nine rovibronic lines of 12C17O for which laboratory wavelengths were previously unavailable were detected in laser-induced fluorescence excitation spectra of the six vibronic bands A1Π(υ' = 0-5)-X1Σ+(υ'' = 0). Rovibronic lines of 12C16O, 13 C16O, 12C17O, and 12C 18O were detected in each band, allowing accurate determination of the unknown wavelengths using neighboring 12C16O and 13C16O lines as reference. The new wavelength data yield consistent heliocentric velocity values when applied to vacuum ultraviolet observations of 12C17O and 12C 18O in the interstellar medium.
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    Accurate laboratory wavelengths of the vacuum ultraviolet A(v'=3)-X(v''=0) band of 12C17O and 12C18O
    (IOP Science, 2003) Steinmann, Christine M.; Rohwer, Erich G.; Stafast, Herbert
    Six individual rotational lines (J'' ≤ 3) of 12C17O, as well as four of 12C18O, were detected in the A 1Π(v' = 3)-X 1Σ+(v'' = 0) vibronic band, and their wavelengths determined using neighboring 12C16O and 13C16O lines as reference. The measurements (fluorescence excitation spectra) were performed in a pulsed supersonic jet (Ar or Ne as carrier gas) employing a tunable pulsed vacuum ultraviolet radiation source with a narrow bandwidth (~5 GHz). The new spectral data on 12C17O and 12C18O are applied to the interpretation of recent vacuum ultraviolet observations of 12C17O and 12C18O in the interstellar medium.
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    Efficiency of Tm3+ -doped silica triple clad fiber laser
    (Optical Society of America, 2011) Ndebeka, Wilfrid Innocent; Heidt, A.; Schwoerer, Heinrich; Rohwer, Erich G.
    We present measurements of the slope efficiency and the pump power at threshold of a Tm3+ -doped silica triple clad fiber laser emitting at 2.02 μm using different cooling techniques. The slope efficiency of 53.6 % was obtained at a temperature of 25oC with a maximum output power of 5 W for 19 W of absorbed power at the pump wavelength of 800 nm and 9.9 W threshold. In a slightly different setup, the output power could be increased to 10 W for an absorbed pump power of 32 W.
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    Investigation of four carbon monoxide isotopomers in natural abundance by laser-induced fluorescence in a supersonic jet
    (Elsevier, 2007) Du Plessis, Anton; Rohwer, Erich G.; Steenkamp, Christine M.
    The four carbon monoxide (CO) isotopomers 12C16O, 13C16O, 12C18O and 12C17O have been detected simultaneously in a CO gas sample of natural isotopic abundance by measuring rovibronic excitation spectra of six vibronic bands in the Fourth Positive System. The CO sample was flow cooled by adiabatic expansion in a pulsed supersonic jet. The rovibronic excitation spectra were obtained using a novel pulsed laser source (pulse duration ∼25 ns, spectral bandwidth ∼5 GHz) continuously tunable in the 139–155 nm vacuum ultraviolet wavelength region for excitation and recording the total fluorescence. In the present paper we report on the spectroscopic results obtained, including transition wavelengths of three forbidden rovibronic bands (e3Σ− − X1Σ+(1, 0), d3Δ − X1Σ+(5, 0), a′3Σ+ − X1Σ+(14, 0)) of 12C16O and band origins of six rovibronic bands (A1Π(v′ = 0–5) − X1Σ+(v″ = 0)) of the rare isotopomer 12C17O, and on the experimental conditions facilitating the high sensitivity of the measurements. The exceptional sensitivity demonstrated by the results has been achieved by fine tuning experimental conditions including the conditions in the supersonic expansion, the jet pulse duration and the laser pulse timing.
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    An overview of the first decade of PollyNET : an emerging network of automated Raman-polarization lidars for continuous aerosol profiling
    (Copernicus Publications on behalf of the European Geosciences Union, 2016) Baars, Holger; Kanitz, Thomas; Engelmann, Ronny; Althausen, Dietrich; Heese, Birgit; Komppula, Mika; Preißler, Jana; Tesche, Matthias; Ansmann, Albert; Wandinger, Ulla; Lim, Jae-Hyun; Ahn, Joon Young; Stachlewska, Iwona S.; Amiridis, Vassilis; Marinou, Eleni; Seifert, Patric; Hofer, Julian; Skupin, Annett; Schneider, Florian; Bohlmann, Stephanie; Foth, Andreas; Bley, Sebastian; Pfüller, Anne; Giannakaki, Eleni; Lihavainen, Heikki; Viisanen, Yrjo; Hooda, Rakesh Kumar; Pereira, Sergio Nepomuceno; Bortoli, Daniele; Wagner, Frank; Mattis, Ina; Janicka, Lucja; Markowicz, Krzysztof M.; Achtert, Peggy; Artaxo, Paulo; Pauliquevis, Theotonio; Souza, Rodrigo A. F.; Sharma, Ved Prakesh; Van Zyl, Pieter Gideon; Beukes, Johan Paul; Sun, Junying; Rohwer, Erich G.; Deng, Ruru; Mamouri, Rodanthi-Elisavet; Zamorano, Felix
    The paper gives an overview of the observations on four continents and two research vessels obtained with eight Polly systems. The specific aerosol types at these locations (mineral dust, smoke, dust-smoke and other dusty mixtures, urban haze, and volcanic ash) are identified by their Ångström exponent, lidar ratio, and depolarization ratio. The vertical aerosol distribution at the PollyNET locations is discussed on the basis of more than 55 000 automatically retrieved 30 min particle backscatter coefficient profiles at 532 nm as this operating wavelength is available for all Polly lidar systems. A seasonal analysis of measurements at selected sites revealed typical and extraordinary aerosol conditions as well as seasonal differences. These studies show the potential of PollyNET to support the establishment of a global aerosol climatology that covers the entire troposphere.
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    White light wavefront control with a spatial light modulator
    (Optical Society of America, 2014-05) Dirk-Mathys, Spangenberg; Dudley, Angela; Neethling, Pieter H.; Rohwer, Erich G.; Forbes, Andrew
    Spatial light modulators are ubiquitous tools for wavefront control and laser beam shaping but have traditionally been used with monochromatic sources due to the inherent wavelength dependence of the calibration process and subsequent phase manipulation. In this work we show that such devices can also be used to shape broadband sources without any wavelength dependence on the output beam’s phase. We outline the principle mathematically and then demonstrate it experimentally using a supercontinuum source to shape rotating white-light Bessel beams carrying orbital angular momentum.