Although a lot of experiments have been done using superfluid helium nanodroplets, as cold matrices for atomic and molecular clusters, very little is known about the shapes and sizes of individual droplets. These were previously only determined indirectly by droplet scattering experiments. Here, we report on the measurements of the shapes and sizes of single He droplets via diffraction imaging using femtosecond X-ray pulses from the Linac Coherent Light Source (LCLS) at SLAC National Accelerator Laboratory. The intensity distribution in the diffraction images was modeled using scattering intensity formula for spheroids. The scattering intensities, radii, aspect ratio and orientation of the helium droplets in the beam will be discussed. We assign the spheroid shape of the droplets to rotational excitation, which in superfluid droplets involves several quantum vortices.

https://conf-slac.stanford.edu/ssrl-lcls-2013/sites/conf-slac.stanford.e...