L Wöste

Publications (61)130.65 Total impact

• Article: Application of parametric time and frequency domain shaping

  S. M. Weber, A. Lindinger, F. Vetter, M. Plewicki, A. Merli, L. Wöste
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  ABSTRACT: We present two novel types of parameterizations for optical control experiments, executed by pulse shaping and evolution strategies on the NaK system. The first is a time domain approach with a pulse parameterization with few, intuitive parameters such as temporal subpulse distances, energies, chirps, and phase differences. It will address the reproducibility and complexity issues that occur when employing non-deterministic algorithms in complex search spaces. The second approach, a transition finder algorithm uses a parameterization in the frequency domain to expose the most important transition frequencies within the laser pulse spectrum, which would not be found otherwise.
  The European Physical Journal D 04/2012; 33(1):39-42. · 1.48 Impact Factor
• Article: Isotopomer selective optimization of 39K85Rb+ and 41K87Rb+ using optimal control

  A. Merli, F. Sauer, L. Wöste, A. Lindinger
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  ABSTRACT: We report on isotope selective three-photon ionization of two isotopomers of KRb by applying evolution strategies. The particularity of this experiment is based on the high resolution phase and amplitude modulation of the fs-laser pulses provided by a 2 × 640pixel pulse shaper. The optimization in a closed feedback loop performed with spectrally broad pulses centered at 840nm shows high enhancements of one isotopomer at the expense of the other isotopomer and vice versa. From the optimal laser field we aim to gain details about the selective ionization sequence and the wavepacket evolution on the involved vibrational states.
  The European Physical Journal D 04/2012; 42(2):217-220. · 1.48 Impact Factor
• Source

  Available from: Albrecht Lindinger

  Article: Spectrally resolved coherent transient signal for ultracold rubidium molecules

  F. Eimer, F. Weise, A. Merli, S. Birkner, F. Sauer, L. Wöste, A. Lindinger, R. Aǧanoǧlu, C. P. Koch, W. Salzmann, T. Mullins, S. Götz, R. Wester, M. Weidemüller
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  ABSTRACT: We present spectrally resolved pump-probe experiments on the photoassociation of ultracold rubidium atoms with shaped ultrashort laser pulses. The pump pulse causes a free-bound transition leading to a coherent transient signal of rubidium molecules in the first excited state. In order to achieve a high frequency resolution the bandwidth of the pump pulse is reduced to a few wavenumbers. The frequency dependence of the transient signal close to the D1 atomic resonance is investigated for characteristic pump-probe delay times. The observed spectra, which show a pronounced dip for pump-probe coincidence, are interpreted using quantum dynamical calculations.
  The European Physical Journal D 04/2012; 54(3):711-714. · 1.48 Impact Factor
• Article: Modelling of HNO3-mediated laser-induced condensation: a parametric study.

  P Rohwetter, J Kasparian, L Wöste, J-P Wolf
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  ABSTRACT: Based on both static (extended Köhler) and dynamic modelling, we investigate the influence of temperature, humidity, HNO(3) initial concentration, as well as of the particle concentration, on the efficiency of HNO(3)-mediated laser-induced condensation. This mechanism is most efficient for low temperatures, high HNO(3) concentration, and relative humidities. It is, however, still active up to 30 °C, down to 70% relative humidity, and below the ppm level of HNO(3). Furthermore, lower particle concentration minimizing the depletion of both HNO(3) and water vapor is more favourable to particle growth.
  The Journal of chemical physics 10/2011; 135(13):134703. · 3.09 Impact Factor
• Article: Influence of pulse duration, energy, and focusing on laser-assisted water condensation

  Y. Petit, S. Henin, J. Kasparian, J. P. Wolf, P. Rohwetter, K. Stelmaszczyk, Z. Q. Hao, W. M. Nakaema, L. Wöste, A. Vogel, T. Pohl, K. Weber
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  ABSTRACT: We investigate the influence of laser parameters on laser-assisted water condensation in the atmosphere. Pulse energy is the most critical parameter. Nanoparticle generation depends linearly on energy beyond the filamentation threshold. Shorter pulses are more efficient than longer ones with saturation at ∼ 1.5 ps. Multifilamenting beams appear more efficient than strongly focused ones in triggering the condensation and growth of submicronic particles, while polarization has a negligible influence on the process. The data suggest that the initiation of laser-assisted condensation relies on the photodissociation of the air molecules rather than on their photoionization.
  Applied Physics Letters 01/2011; 98(4):041105-041105-3. · 3.84 Impact Factor
• Source

  Available from: Stefano Henin

  Article: Field measurements suggest the mechanism of laser-assisted water condensation.

  S Henin, Y Petit, P Rohwetter, K Stelmaszczyk, Z Q Hao, W M Nakaema, A Vogel, T Pohl, F Schneider, J Kasparian, K Weber, L Wöste, J-P Wolf
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  ABSTRACT: Because of the potential impact on agriculture and other key human activities, efforts have been dedicated to the local control of precipitation. The most common approach consists of dispersing small particles of dry ice, silver iodide, or other salts in the atmosphere. Here we show, using field experiments conducted under various atmospheric conditions, that laser filaments can induce water condensation and fast droplet growth up to several μm in diameter in the atmosphere as soon as the relative humidity exceeds 70%. We propose that this effect relies mainly on photochemical formation of p.p.m.-range concentrations of hygroscopic HNO(3), allowing efficient binary HNO(3)-H(2)O condensation in the laser filaments. Thermodynamic, as well as kinetic, numerical modelling based on this scenario semiquantitatively reproduces the experimental results, suggesting that particle stabilization by HNO(3) has a substantial role in the laser-induced condensation.
  Nature Communications 01/2011; 2:456. · 7.40 Impact Factor
• Article: Time‐resolved TPI‐Spectroscopy of the B‐ and D‐State of Na3‐Clusters

  E. Schreiber, H. Kühling, K. Kobe, S. Rutz, L. Wöste
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  ABSTRACT: The dynamical behaviour of excited states of cold Na3-clusters in the gas phase was investigated in a transient two-photon-ionization (TPI)-experiment, employing picosecond pump technique followed by mass-selective detection. The results exhibit for the first time the pseudo-rotational motion of the B-state as a temporal sequence. The precise measurement of the beat frequencies affirms a pseudo-Jahn-Teller-model for the interpretation of the spectroscopic data. For the D-state, known to predissociate very rapidly the temporal evolution of fragmentation directly could be observed. Decay-times of the TPI-signal were estimated to be in the order of 5 picoseconds.
  Berichte der Bunsengesellschaft für physikalische Chemie. 05/2010; 96(9):1301 - 1305.
• Article: Saturation of the filament density of ultrashort intense laser pulses in air

  S. Henin, Y. Petit, J. Kasparian, J.–P. Wolf, A. Jochmann, U. Schramm, S. Bock, S. D. Kraft, R. Sauerbrey, W. M. Nakaema, K. Stelmaszczyk, P. Rohwetter, L. Wöste, Ch.-L. Soulez, S. Mauger, L. Bergé, S. Skupin
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  ABSTRACT: We experimentally and numerically characterize multiple filamentation of laser pulses with incident intensities of a fewTW/cm2. Propagating 100 TW laser pulses over 42 m in air, we observe a new propagation regime where the filament density saturates. As also evidenced by numerical simulations in the same intensity range, the total number of filaments is governed by geometric constraints and mutual interactions among filaments rather than by the available power in the beam.
  Applied Physics B 03/2010; 100:77. · 2.19 Impact Factor
• Article: Matrix-assisted laser desorption/ionization by using femtosecond laser pulses in the near-infrared wavelength regime.

  J M Wichmann, C Lupulescu, L Wöste, A Lindinger
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  ABSTRACT: We observe a substantial matrix-assisted laser desorption/ionization (MALDI) signal when irradiating femtosecond laser pulses in the near-infrared spectral range centered around 800 nm and using standard MALDI matrices with absorption bands in the ultraviolet (UV) regime. The laser pulse energy dependence of this novel phenomenon is investigated in comparison with MALDI with near-UV laser pulses. Our observations show that multiphoton absorption/ionization could be a major issue among the MALDI processes when the sample is irradiated with ultra-short laser pulses.
  Rapid Communications in Mass Spectrometry 04/2009; 23(8):1105-8. · 2.79 Impact Factor
• Article: Towards Supercontinuum Cavity Ring-Down Spectroscopy

  K. Stelmaszczyk, M. Fechner, P. Rohwetter, M. Queißer, A. Czyżewski, T. Stacewicz, L. Wöste
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  ABSTRACT: We report on measurements performed with the broadband variant of Cavity Ring-Down Spectroscopy based on white-light Supercontinuum. Generated by filaments in a quartz block, the Supercontinuum was coupled into the stable optical cavity characterized by a high Q-factor of 104. The ring-down transients of selectively chosen wavelengths were registered sequentially, revealing a difference of their decay times. The demonstrated high precision of decay time measurement (10−4 relative error) opens the perspective for multiwavelength detection of absorbing species with sub ppb (10−9) sensitivity in the unprecedented broad spectral range of Supercontinuum. This is why we intend to call this technique Supercontinuum Cavity Ring-Down Spectroscopy. Finally, we used the Supercontinuum to quantify variations of the wavelength-dependent reflection coefficient of cavity mirrors; as we show, with an absolute accuracy of 10−6.
  Applied Physics B 02/2009; 94(3):369-373. · 2.19 Impact Factor
• Chapter: Filament-induced electric events in thunderstorms

  J. Kasparian, R. Ackermann, Y. -B. André, G. Méchain, G. Méjean, B. Prade, P. Rohwetter, E. Salmon, L. A. Schlie, K. Stelmaszczyk, J. Yu, A. Mysyrowicz, R. Sauerbrey, L. Wöste, J. -P. Wolf
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  ABSTRACT: Under conditions of high electric field during two thunderstorms, we observed a statistically significant number of electric events synchronized with the ionized filaments generated by ultrashort laser pulses in the atmosphere. This observation suggests that corona discharges have been triggered by filaments.
  12/2008: pages 967-969;
• Article: Coherent transients in the femtosecond photoassociation of ultracold molecules.

  W Salzmann, T Mullins, J Eng, M Albert, R Wester, M Weidemüller, A Merli, S M Weber, F Sauer, M Plewicki, F Weise, L Wöste, A Lindinger
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  ABSTRACT: We demonstrate the photoassociation of ultracold rubidium dimers using coherent femtosecond pulses. Starting from a cloud of ultracold rubidium atoms, electronically excited rubidium molecules are formed with shaped photoassociation pump pulses. The excited state molecules are projected with a time-delayed probe pulse onto molecular ion states which are detected in a mass spectrometer. Coherent transient oscillations of the excited state population are observed in the wings of the pump pulse, in agreement with the time-dependent solution of the Schrödinger equation of the excitation process.
  Physical Review Letters 06/2008; 100(23):233003. · 7.37 Impact Factor
• Article: Laser multiple filamentation control in air using a smooth phase mask

  P. Rohwetter, M. Queißer, K. Stelmaszczyk, M. Fechner, L. Wöste
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  ABSTRACT: We report on experimental results revealing the important role of linear diffraction in multiple filamentation of intense laser pulses propagating in air. We show that during the early stages of propagation the transverse energy redistribution is governed by the laws of classical optics, defining the initial conditions for subsequent filamentary breakup of the beam. This is done by introducing a smoothly varying transverse phase, resulting in deterministic multiple filamentation. The observations presented here indicate precise wave-front shaping as a way to control the highly nonlinear and otherwise turbulent aforesaid process, which is a prerequisite for a number of applications.
  Phys. Rev. A. 01/2008; 77(1).
• Article: Gas Phase Infrared Spectroscopy of Mass-Selected Vanadium Oxide Cluster Anions

  G. Santambrogio, M. Brümmer, L. Wöste, J. Döbler, M. Sierka, J. Sauer, G. Meijer, K. R. Asmis
  Phys. Chem. Chem. Phys. 01/2008; 10:3992-4005.
• Article: Multi-objective optimization on alkali dimers

  S. M. Weber, F. Sauer, M. Plewicki, A. Merli, L. Wöste, A. Lindinger
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  ABSTRACT: We present experimental results of a multi-objective evolutionary algorithm that controls the ionization of the NaK molecule and the fragmentation/ionization of potassium dimers. The two physically contradictive goals are dimer ionization and fragmentation into the atomic isotopes. In the NaK case, we use an approach to simplify the usually complex results of feedback-loop coherent control experiments and implement the ‘pulse cleaning’ method. It defines the objective function in a way that unnecessary spectral features are reduced and the most important vibronic transitions are enhanced. This method will be developed in terms of a classical multi-objective optimization and we present some corresponding Pareto-optimal solutions.
  Journal of Modern Optics 11/2007; 54(Nos. 16-17):2659-2666. · 1.17 Impact Factor
• Article: High resolution coherent control measurements on KRb

  F. Sauer, A. Merli, L. Wöste, and A. Lindinger
  Chemical Physics 01/2007; 334:138. · 1.90 Impact Factor
• Article: Optimal control of multiphoton ionization of Rb2 molecules in a magneto-optic trap

  F. Weise, S. Birkner, A. Merli, S. M. Weber, F. Sauer, L. Wöste, A. Lindinger, W. Salzmann, T. G. Mullins, J. Eng, M. Albert, R. Wester, and M. Weidemüller
  Physical Review A 01/2007; 76:063404. · 2.88 Impact Factor
• Article: Isomorphous substitution in bimetallic oxide clusters.

  E Janssens, G Santambrogio, M Brümmer, L Wöste, P Lievens, J Sauer, G Meijer, K R Asmis
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  ABSTRACT: The geometric and electronic structure of bimetallic oxide clusters is studied as a function of their composition with gas phase vibrational spectroscopy. Infrared multiple photon dissociation spectra of titanium-vanadium oxide cluster anions are measured in the 500 to 1200 wave number range and assigned on the basis of harmonic frequencies calculated using density functional theory. Singly substituted (V(2)O(5))(n-1)(VTiO(5))(-) (n=2-4) cluster anions are shown to form polyhedral caged structures similar to those predicted for their isoelectronic counterparts, the neutral (V(2)O(5))(n) clusters. Upon systematic exchange of V by Ti atoms in V(4-n)Ti(n)O(-)(10) (n=1-4), the structure does not change. The stress induced by the isomorphous substitution results in an increased number of unpaired electrons (n-1) for the Ti-rich systems, leading to a quartet ground state for Ti(4)O(-)(10).
  Physical Review Letters 07/2006; 96(23):233401. · 7.37 Impact Factor
• Source

  Available from: Guillaume Méjean

  Article: Influence of negative leader propagation on the triggering and guiding of high voltage discharges by laser filaments

  R. Ackermann, G. Méchain, G. Méjean, R. Bourayou, M. Rodriguez, K. Stelmaszczyk, J. Kasparian, J. Yu, E. Salmon, S. Tzortzakis, Y.-B. André, J.-F. Bourrillon, L. Tamin, J.-P. Cascelli, C. Campo, C. Davoise, A. Mysyrowicz, R. Sauerbrey, L. Wöste, J.-P. Wolf
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  ABSTRACT: The triggering and guiding of negative discharges using filaments induced by a femtosecond-terawatt laser pulse have been studied in sphere-plane gaps up to 4.5meters. Fast-frame camera pictures allow the evaluation of the influence of the negative leader propagation on the triggering and guiding process. We show that the plasma channel can either trigger a space-leader discharge or act as a guiding path for the negative leader head. For the latter case the results suggest a linear dependence of the guided lengths up to 2.4m, while the formation of a space-leader reduces this guided length by up to 50%. This effect is explained by the limited plasma lifetime of the filament that is measured to be about 1μs.
  Applied Physics B 02/2006; 82(4):561-566. · 2.19 Impact Factor
• Source

  Available from: Guillaume Méjean

  Article: Propagation of fs TW laser filaments in adverse atmospheric conditions

  G. Méchain, G. Méjean, R. Ackermann, P. Rohwetter, Y.-B. André, J. Kasparian, B. Prade, K. Stelmaszczyk, J. Yu, E. Salmon, W. Winn, L. A. Schlie, A. Mysyrowicz, R. Sauerbrey, L. Wöste, J.-P. Wolf
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  ABSTRACT: The propagation of femtosecond terawatt laser pulses at reduced pressure (0.7 atm) is investigated experimentally. In such conditions, the non-linear refractive index n 2 is reduced by 30%, resulting in a slightly farther filamentation onset and a reduction of the filament number. However, the filamentation process, especially the filament length, is not qualitatively affected. We also show that drizzle does not prevent the filaments from forming and propagating.
  Applied Physics B 01/2005; 80(7):785-789. · 2.19 Impact Factor