Tuesday 5 pm (Freiburg) / 8 am (Vancouver)
26.07.2022 – Mengxing Na & Alex Wang, UBC Vancouver (Canada)
Mengxing (Ketty) Na
Evolution of non-thermal electrons in pump-probe electron relaxation dynamics
Time- and angle-resolved photoemission spectroscopy (TR-ARPES) accesses the electronic structure of solids under optical excitation, and is a powerful technique for studying the coupling between electrons and collective modes. Using TR-ARPES, it has been recently demonstrated that electron-phonon coupling can be extracted from the non-thermal occupation of electrons arising from photoexcitation and subsequent phonon scattering. It is therefore desirable to make a precise estimation of the non-thermal window within which such features arise, and effective temperature models may not be applied. We show that Boltzmann rate equations can be used to calculate the time-dependent electronic occupation function, and reproduce experimental features given by non-thermal electron occupation. Using this model, we define a quantitative measure of non-thermal electron occupation and use it to define distinct phases of electron relaxation in the fluence-delay phase space. More generally, this approach can be used to inform the non-thermal-to-thermal crossover in pump-probe experiments.
Chair: David Jones
Alex Wang
Computational Studies of Extreme Bonding: Fringe Bonds, σ Conductance, and Unconventional Aromaticity
This talk will provide answers to the following seven questions theoretically:
1) How long a C-C s single bond can be?
2) Can two sp2 C atoms form only s bonds?
3) Are antibonding orbitals always more stable than bonding orbitals?
4) Can a saturated organic material have good electric conductivity through a σ network?
5) Can a H atom participate in an aromatic p bond?
6) Is the transition state (activated complex) always unobservable?
7) What can such crazy ideas have anything to do with the real world?
Historical Background of the Aforementioned Seven Questions
Several years ago, my group studied the intramolecular hydrogen-bond (IHB) systems in acetylacetone and its α-halo derivatives [PCCP 18, 344 (2016)]. We found that the IHB proton transfer is an early, sudden quantum tunneling process without going through the classical C2v transition state whereas virtually all textbooks have been claiming the opposite on this subject. More amazingly, the classical C2v transition state of the IHB proton transfer is aromatic! What is its significance? It is the first ever identified aromatic π system (albeit only a transition state) involving a H atom! Since then, we have designed several new ground-state aromatic H-π systems.
Inspired by our expedition in unconventional aromaticity, we have been wondering how extremely we can push the length limit of a common chemical bond without breaking it. For instance, the longest C−C single σ bond that has been realized experimentally is slightly above 2.04 Å in length [JACS 143, 14360 (2021)] whereas the predicted longest C−C bond is about 2.33 Å in drum-shaped propellanes [JACS 119, 1449 (1997)]. Very recently, we have successfully designed a series of new saturated organic molecules [JPCA 125, 933 (2021)], in which two sp2 C atoms can form an extremely long C−C σ bond with a world-record ca. 3.39 Å bond length. Computational studies have predicted the band gaps of corresponding saturated organic polymers (made from the monomers with the long C−C σ bond) to be within 0.28~12.23 eV, which encloses nearly the entire range of band gaps of those unsaturated conducting organic polymers currently in use.
Chair: Takamasa Momose
19.07.2022 – Klaus Bartschat, Drake University, Iowa (USA)
Klaus Bartschat
Coherent Control and Attosecond Dynamics with Pulsed XUV and IR Radiation
The enormous advances in the generation of advanced light sources have enabled the exploration of the ultrafast dynamics in atoms and molecules, thereby promising a rich field of possibilities in the control of matter. One aim of quantum coherent control is to steer electronic motion in atoms and molecules in specific directions or locations. This might be achieved by introducing a controlled delay between two or more pulses. Other applications of such delays are RABBITT (Reconstruction of Attosecond Beating By Interference of Two-photon Transitions) setups, which have also been extended to more than two photons.
We discuss a variety of schemes by which control of the PAD asymmetry can be achieved, such as interfering one-photon and two-photon ionization pathways in a region of an intermediate resonance, overlapping the XUV pulse with an infrared (IR) field as in RABBITT, or using circularly polarized light. Employing circularly polarized light opens up a number of particularly interesting possibilities in the study of multi-photon ionization processes, such as the investigation of circular dichroism when two fields can either be co-rotating or counter-rotating.
Finally, few-cycle elliptically polarized pulses can be employed in so-called “attoclock setups” to investigate the tunneling time in strong-field ionization to test whether tunneling ionization is instantaneous or how one might define a delay. Given that time is a parameter rather than an observable in standard Quantum Mechanics, this is a fundamental question that has raised significant interest in recent years.
12.07.2022 – Ilsa Cooke, UBC Vancouver (Canada)
Ilsa Cooke
Probing chemical reactions in the interstellar molecular cloud TMC-1 – combined observational and laboratory efforts
Molecules are not limited to our solar system but exist in the extreme environments found in interstellar space. Astrochemistry is the study of this rich and diverse chemistry that occurs throughout the universe. Our picture of the molecular universe is becoming increasingly complex with around 250 molecules identified in the interstellar medium, and the rate of new detections is still growing.
Dense molecular clouds are the earliest stage of star formation and provide the molecular material that will make up new planets and solar systems. I will present our recent observations of a particular molecular cloud in Taurus, TMC-1, including the detection of the first interstellar polycyclic aromatic hydrocarbons. In order to understand how these molecules can form in TMC-1, laboratory experiments must be conducted down to temperatures below 10 K to measure the kinetics of key reactions. The study of reactions at these low temperatures, including measurements of the reaction rate coefficients and product-branching-ratios, presents substantial experimental challenges. I will discuss the implementation of the CRESU technique (a French acronym for Reaction Kinetics in Uniform Supersonic Flow) as a method to measure low-temperature reaction kinetics relevant to interstellar space.
05.07.2022 – Cristian Manzoni, IFN-CNR Politecnico Milano (Italy)
Cristian Manzoni
Hyperspectral Imaging and Microscopy
Spectral imaging, also known as imaging spectroscopy, refers to methods and devices for acquiring a complete light spectrum for each point in the image of a scene. It provides much richer information with respect to standard imaging, enabling to identify materials or detect dynamical processes. Spectral imaging has been applied to a wide range of scientific investigations, such as remote sensing, pigment determination in biology, medicine, coastal ocean imaging, water analysis, agriculture, cultural heritage and archaeology, just to cite a few. In particular, hyperspectral imaging aims at acquiring the whole continuous spectrum of each point of the scene. A powerful approach to this aim is to combine classical imaging with Fourier-transform spectrometry [1].
In this talk, I will describe the main properties of the spectral imaging and the current acquisition approaches. I will also show the most recent advancements obtained at the Istituto di Fotonica e Nanotecnologie (IFN-CNR), based on an innovative optical device [2].
Our compact hyperspectral system is able to acquire spectral reflectance and fluorescence images with high sensitivity, broad spectral coverage and high spectral resolution. Examples of hyperspectral remote-sensing and microscopy images will be provided and discussed [3].
References
[1] S.P. Davis, M.C. Abrams, and J.W. Brault, Fourier Transform Spectrometry (Academic Press, 2001)
[2] D. Brida, C. Manzoni, and G. Cerullo, “Phase-locked pulses for two-dimensional spectroscopy by a birefringent delay line,” Opt. Lett. 37, 3027-3029 (2012)
[3] A. Perri, B. E. Nogueira de Faria, D. C. Teles Ferreira, D. Comelli, G. Valentini, F. Preda, D. Polli, A. M. de Paula, G. Cerullo, and C. Manzoni, “Hyperspectral imaging with a TWINS birefringent interferometer,” Opt. Express 27, 15956-15967 (2019)
Chair: Giuseppe Sansone
28.06.2022 – Nadine Borduas-Dedekind, UBC Vancouver (Canada)
Nadine Borduas-Dedekind
On the photophysics of molecular oxygen (O2) at ambient temperature and pressure: The production of singlet oxygen and its presence in outdoor and indoor atmospheric organic aerosols
Molecular oxygen (O2), in its triplet ground state 3Σ−g, accounts for 21% of our atmosphere and is at the origin of life on Earth. O2 therefore creates an oxidative atmosphere where volatile organic compounds and atmospheric aerosols are oxidized and aged. O2 is involved in major atmospheric chemistry cycles such as generation of the ozone layer, smog ozone production, OH radical formation and photosynthesis.
The first excited state of triplet state O2 is singlet state 1O2 (1Δg), requiring an energy of 95 kJ/mol. This oxidant is formed naturally in the environment, for example during photosynthesis as well as in sunlit waters from indirect photochemistry of dissolved organic matter. Based on this latter mechanism, we speculated that 1O2 could also be formed in the atmosphere from atmospheric organic aerosols, specifically containing chromophoric moieties termed atmospheric brown carbon.
To study the photo-production of 1O2 in the atmosphere, we generated secondary organic aerosols from aromatic anthropogenic precursors in a laboratory smog chamber as a proof-of-concept. We then extracted the collected aerosol filters and submitted the soluble extracts to atmospherically-relevant photochemical conditions of UVA and UVB light at room temperature. Using furfuryl alcohol as a probe for 1O2, we determined steady-state concentrations of this oxidant using liquid chromatography and calculated 1O2 quantum yields for each aerosol sample. We find that molecules such as amino acids, organo-nitrogen compounds and phenolic compounds have a shortened lifetime by more than half when 1O2 reactivity is taken into consideration. We recently extended our work to the photoproduction of 1O2 in ambient PM10 filter samples in Switzerland and its source apportionment. We demonstrate a seasonality of 1O2 that peaks in the wintertime and coincides with peak absorbance of brown carbon emitted from biomass burning processes. In addition, we identified sources of 1O2 in indoor air in cooking aerosols. The aim of this research program on atmospheric 1O2 is to characterize its understudied role in atmospheric chemistry and determine its role in the oxidative capacity of the atmosphere for predictive capabilities.
21.06.2022 – Fabian Meyer, Fraunhofer ISE, Freiburg
Fabian Meyer
Observing femtosecond laser ablation of Silicon with pump-probe microscopy
Laser ablation with ultrashort pulsed lasers is a means to controllably remove material from the surface of virtually any substrate in order to micromachine, to structure or to functionalize its surface. For the manufacture of silicon solar cells it is a now widespread technology to locally open thin dielectric layers as a cost-effective and eco-friendly alternative to mask-and-etch techniques. However, the temporarily high temperatures, high pressures and high excitation levels that are reached in the process can damage the solar cell and lower its efficiency. In this talk, I would like to show how we use pump-probe microscopy to observe the sample in-situ during laser ablation with sub-picosecond resolution. We analyze the excitation of the silicon surface, melting and rapid solidification as well as different modes of ablation. The method has proven valuable to measure transient side-effects of the ablation process and has enabled us to tune the laser process towards the application in a more educated manner.
Chair: Katrin Erath
14.06.2022 – Brendan Moore & Pinrui Shen
Brendan Moore, UBC Vancouver
„UV Photodissociation of Amino Acids in a Solid Parahydrogen Matrix“
Chair: Takamasa Momose
Pinrui Shen, UBC Vancouver
„Precision measurement of the velocity averaged collision cross-section with cold atom sensors“
Chair: Kirk Madison
31.05.2022 – Ian MacPhail-Bartley
Ian MacPhail-Bartley, UBC Vancouver
„Rotational control of molecular systems for the study of many-body quantum dynamics“
Chair: Valery Milner
26.04.2022 – Eric Brunner & Cristian Medina Hernandez
Eric Brunner, University of Freiburg
„Many-body coherence and entanglement from randomized correlation measurements“
Chair: Andreas Buchleitner / Christoph Dittel
Cristian Medina Hernandez, University of Freiburg
„Strong-field nanoplasma ignition of doped He clusters using extreme light sources.“
Chair: Frank Stienkemeier
05.04.2022 – Samuel Kellerer
Samuel Kellerer, University of Feiburg
„Nonlinear Attosecond XUV Coincidence Spectroscopy“
Chair: Giuseppe Sansone
29.03.2022 – Ioannis Makos
Ioannis Makos, University Freiburg
„Probing electronic correlation with attosecond XUV pulses using a Reaction Microscope“
Chair: Giuseppe Sansone
22.03.2022 – Mathieu Isoard
Mathieu Isoard, University Freiburg
„Analogue gravity in a nutshell„
Chair: Andreas Buchleitner
15.03.2022 – Timur Tscherbul
Timur Tscherbul
„Robust nuclear spin entanglement via electric dipolar interactions in polar molecules“
Chair: Roman Krems / UBC
08.03.2022 – Olesya Ablyasova & Moritz Michelbach
Olesya Ablyasova
„Electronic states of manganese oxide and calcium manganese oxide clusters“
Chair: Tobias Lau
Moritz Michelbach
„Cluster isolation spectroscopy of polyacenes“
Chair: Frank Stienkemeier
01.03.2022 – Max Flach & Dominik Lentrodt
Max Flach
„Diatomic gas phase iron halide cations, a model system to reveal chemical shifts beyond the oxidation state“
Chair: Tobias Lau
Dominik Lentrodt
„X-ray quantum optics with Mössbauer nuclei“
Chair: Andreas Buchleitner
15.02.2022 – R.K. Kathir
R. K. Kathir
„Theoretical studies on dynamics of spin-states in singlet fission“
Chair: Michael Thoss
08.02.2022 – Aleksandr Demianenko and Sarang Dev Ganeshamandiram
Aleksandr Demianenko
„Photo-activated processes and charge transfer in aggregates of organic molecules attached to rare gas clusters„
Chair: Frank Stienkemeier
Sarang Dev Ganeshamandiram
„Extreme ultraviolet wavepacket interferometry using table-top high harmonic generation„
Chair: Lukas Bruder
01.02.2022 – Barbara Merzuk and Andreas Woitzik
Barbara Merzuk
„Investigating the formation of multi charger Krypton ions in resonant and non-resonant Auger decay“
Chair: Giuseppe Sansone
Andreas Woitzik
„Quantum state preparation in a micromaser„
Chair: Andreas Buchleitner
25.01.2022 – Daniel Hönig and Aaron Ngai
Daniel Hönig
„Trapping Barium Ions and Ion-Coulomb-Crystals with Optical Fields“
Chair: Tobias Schätz/Amir Mohammadi
Aaron Ngai
„Coherent control of molecularphotoionization at the FERMI Free-Electron-Laser“
(Chair: Frank Stienkemeier)
18.01.2022 – Friedemann Landmesser and Fabian Thielemann
Friedemann Landmesser
„Multiple-quantum fluorescence signals in thermal alkali vapors“
Chair: Frank Stienkemeier
Fabian Thielemann
Ultracold interaction between a single Barium ion and an atomic gas of Lithium“
Chair: Tobias Schätz
11.01.2022 – Meet & Greet / Tobias Sixt
Tobias Sixt
„Quantum-state-controlled Penning collisions between metastable helium and lithium atoms“
Chair: Katrin Erath
