Imaging the shapes and dynamics of superfluid helium nanodroplets

This thesis addresses the three-dimensional (3D) structure determination of individual nanoparticles or, more precisely, helium nanodroplets, via scattering of extreme-ultraviolet light pulses. In particular, the recent development of free-electron lasers (FELs) delivering intense short-wavelength light pulses of femtosecond duration is a promising prospect for the study of unsupported particles such as proteins, nucleic acids, viruses, and also droplets on the nanometer scale. Motivated by this potential application in imaging of biomolecules, the thesis investigates superfluid helium nanodroplets in an experiment at the FERMI FEL that is focused on the interaction of intense light pulses with matter by analyzing wide-angle scattering patterns. The experiment can be divided in two parts: In the first part, the complete 3D droplet shapes are retrieved from the diffraction patterns, enabling a comparison with theory. Despite the absence of friction in a superfluid, it is shown that the shapes of spinning superfluid helium nanodroplets resemble those of rotating normal liquid drops. Also the evolution of the droplet shapes from spherical to oblate, prolate, and even two-lobed configurations is observed. In the second part of the experiment, scattering images of xenon doped helium nanodroplets are recorded after irradiating the droplets with intense near-infrared laser pulses to study the light induced dynamics. The diffraction patterns indicate density fluctuations in the droplets that occur as the energy of the laser pulse is deposited at the locations of the dopant atoms. The density fluctuations are further explored for two selected cases: (i) A random distribution of the fluctuations when the dopants are also randomly distributed in the droplet, and (ii) a structured distribution of the fluctuations when the dopants accumulate at specific sites, which is probably connected to the occurrence of quantized vortices in the spinning superfluid droplet.

Author dc:creator

• Langbehn, Bruno

Advisors dc:contributor.advisor

• Möller, Thomas
• Rupp, Daniela

Licence dc:rights.uri

• https://creativecommons.org/licenses/by/4.0/

Language dc:language.iso

en

Identifier URI

http://dx.doi.org/10.14279/depositonce-11984

OAI identifier oai:identifier

oai:depositonce.tu-berlin.de:11303/13189