Aaron Ngai
A5008761314- Quantum, superfluid, helium dynamics
- Advanced Chemical Physics Studies
- Cold Atom Physics and Bose-Einstein Condensates
- Laser-Matter Interactions and Applications
- Quantum optics and atomic interactions
- Spectroscopy and Quantum Chemical Studies
- Atomic and Subatomic Physics Research
- Terahertz technology and applications
- Atomic and Molecular Physics
- Advanced Fiber Laser Technologies
- Laser-Plasma Interactions and Diagnostics
- Advanced X-ray Imaging Techniques
- Particle Accelerators and Free-Electron Lasers
- Mass Spectrometry Techniques and Applications
University of Freiburg
2021-2025
Abstract Roaming reactions involving a neutral fragment of molecule that transiently wanders around another before forming new bond are intriguing and peculiar pathways for molecular rearrangement. Such can occur example upon double ionization small organic molecules, have recently sparked much scientific interest. We studied the dynamics $$\hbox {H}_2$$ -roaming reaction leading to formation {H}_3^+$$ after two-photon ethanol 2-aminoethanol, using an XUV-UV pump-probe scheme. For ethanol,...
Abstract We present a compact, intrinsically stable common path interferometer for the seeding of free-electron lasers (FELs). The can handle required ultraviolet seed wavelengths and features an excellent phase stability 10 mrad at 265 nm. By FEL FERMI, we demonstrate generation extreme (XUV) pulse pairs with tunable delay 6 as 52.5 Prospective applications are Fourier transform spectroscopy, nonlinear spectroscopy coherent control experiments in XUV x-ray domain.
Bubbles in helium droplets form around excited atoms and greatly accelerate interatomic Coulombic decay, showing how environment enhances this biologically relevant energy-sharing process among molecules.
The relaxation dynamics of superexcited superfluid He nanodroplets is thoroughly investigated by means extreme-ultraviolet (XUV) femtosecond electron and ion spectroscopy complemented time-dependent density functional theory (TDDFT). Three main paths leading to the emission electrons ions are identified: Droplet autoionization, pump-probe photoionization, autoionization induced re-excitation droplets relaxing into levels below droplet ionization threshold. most abundant product both...
Tailored light-matter interactions in the strong coupling regime enable manipulation and control of quantum systems with up to unit efficiency
Superfluid helium nanodroplets are often considered as transparent and chemically inert nanometer-sized cryo-matrices for high-resolution or time-resolved spectroscopy of embedded molecules clusters. On the other hand, when resonantly excited with XUV radiation, a multitude ultrafast processes initiated, such relaxation into metastable states, formation nanoscopic bubbles excimers, autoionization channels generating low-energy free electrons. Here, we discuss full spectrum observed...
We present single-shot electron velocity-map images of nanoplasmas generated from doped helium nanodroplets and neon clusters by intense near-infrared mid-infrared laser pulses. report a large variety signal types, most crucially depending on the cluster size. The common feature is two-component distribution for each single-cluster event: A bright inner part with nearly circular shape corresponding to energies up few eV, surrounded an extended background more energetic electrons. total...
Tailored light-matter interactions in the strong coupling regime enable manipulation and control of quantum systems with up to unit efficiency, applications ranging from information photochemistry. While are readily induced at valence electron level using long-wavelength radiation, comparable phenomena have been only recently observed short wavelengths, accessing highly-excited multi-electron inner-shell states. However, strong-field processes wavelengths has not possible, so far, due lack...
We present a method for the reconstruction of ion kinetic energy distributions from time-of-flight mass spectra through trajectory simulations. In particular, this is applicable to complicated spectrometer geometries with largely anisotropic collection efficiencies. A calibration procedure using single peak allows accurate determination parameters related calibration, experimental alignment, and instrument response function, which improves agreement between simulations experiment. The...