Tuesday 4:30 pm (Freiburg) / 7:30 am (Vancouver)
16.04.25 – Josef Tiggesbäumker, University of Rostock
29.04.25 – Sitanath Mondal, University of Freiburg & Tobias Heldt, MPI Heidelberg
06.05.25 – Pascal Pessier, University of Kiel
13.05.25 – Dimitris Charalambidis, University of Crete, Greece
27.05.25 – Federico Vismarra, ETH Zurich, Switzerland
08.07.25 – Philipp Lunt, University of Heidelberg
06.05.25 – Pascal Pessier, University of Kiel
Taking Molecular Photoswitches to the Gas Phase – Insights into Ultrafast Dynamics of Azobenzene Derivatives
To observe the pure ultrafast dynamics of photochromic molecular switches following photoexcitation in the absence of any overshadowing solvent effects, systematic investigations of these photoswitches need to be conducted in the gas phase. Here, I will present parts of my research on two subclasses of molecular switches in the gas phase using femtosecond time-resolved time-of-flight mass spectrometry and photoelectron imaging. The selected photoswitches presented here were derived from alteration of the archetypical azobenzene structure: substitution of one phenyl ring by a pyridyl ring and bridging of the phenyl rings. The former, the three isomers of phenylazopyridine, 2-PAPy, 3-PAPy and 4-PAPy, were chosen as representatives of the class of heteroaryl azo dyes and will illustrate the importance of solvent-free investigations. The latter, the -C2H4-bridged diazocine, revealed fascinating behavior due to the influence of the bridging unit.
Chair: Lukas Bruder
29.04.25 – Sitanath Mondal, University of Freiburg & Tobias Heldt, MPI Heidelberg
Sitanath Mondal
Single and double ionization of pyridine and pyridine clusters:
Radiation damage on genetic materials is a very important field of research. Photoionization studies of small bio molecular building blocks and their analogues can contribute by giving insights into energetics and dynamics of formation pathways of secondary electrons and the corresponding cationic dissociation reactions. Here, I present a double imaging photoelectron photoion coincidence study of pyridine, pyridine clusters and pyridine-water complexes, mimicking in vivo environments. From our mass-selected photoelectron spectra different fragmentation channels can be assigned to the corresponding cationic states. An additional analysis of electron-ion-ion coincidences allows us to obtain similar data for dicationic states of the molecules, revealing metastable decay channels and initial insights into stepwise dissociation pathways. For pyridine-water complexes this approach allows distinguishing between different local and non-local double ionization mechanisms like Intermolecular Coulombic Decay (ICD).
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Tobias Heldt
Intra-cavity photoionization with intense transient standing waves
To study nonlinear light-matter interactions such as multiphoton or tunnel ionization, intense light fields are essential. Using a femtosecond enhancement cavity for a near-infrared frequency comb, we are able to achieve intensities exceeding 1013 W/cm2 at a repetition rate of 100 MHz. The bow-tie cavity supports counter-propagating pulses that form a transient standing wave at the focus. A gas nozzle and a velocity-map imaging (VMI) spectrometer are integrated to analyze the angular distribution of the emitted photoelectrons [1].
At the antinodes of the standing wave, constructive interference results in a doubling of the maximum intensity compared to single pulse operation. Additionally, the ionization region along the beam propagation is minimized as it is determined by the <200 fs pulse overlap rather than the Rayleigh length. This reduction of the focal volume allows momentum imaging without electrostatic focusing [2].
Furthermore, the electrons are diffracted by the structured ponderomotive potential of the standing wave. This phenomenon, known as the Kapitza-Dirac effect, changes the momentum distribution of the photoelectrons. I will discuss different regimes and descriptions of this effect, ranging from a classical perspective to an interference picture, and present recent experimental findings.
[1] J.-H. Oelmann et al., Rev. Sci. Instrum., 93(12), 123303 (2022)
[2] T. Heldt et al, Opt. Lett. 49, 6825-6828 (2024).Chair: Sebastian Hartweg & Andreas Buchleitner
16.04.25 – Josef Tiggesbäumker, University of Rostock
HS II, 10:00 am
It’s all about plasmons – From polyanionic nanoparticles to nanoscaled plasmas
Understanding the collective response of matter to the effect of light is important for basic research and also offers a wide range of possibilities for applications. Clusters as a link between atoms and solids are of particular interest in this context, as their physical and chemical properties can be adjusted almost arbitrarily via material and particle size. Using the example of the charge state and utilizing particle traps and high-resolution diagnostics, we will show what effects plasmons cause in strongly negatively and extremely positively charged systems and how these experiments contribute to our understanding of the underlying processes and their dynamics.
Chair: Frank Stienkemeier
