For non-destructive imaging of three-dimensional (3D) materials and biological specimen, hard xray
in-line holography is particularly suitable, since it offers a phase-sensitive imaging scheme
which can cover large specimen in a full-field approach without the need for scanning.
Unfortunately, the resolution of holographic imaging is limited by the source size of the cone-beam
illumination, and does not reach values in the sub-20 nm regime which are routinely achieved by
ptychography or CDI. We have developed two novel imaging schemes for hard x-ray microscopy.
We have simulated the novel techniques and demonstrated sub-10 nm spatial resolution
experimentally.
First we demonstrate a new approach of full-field holographic x-ray imaging based on cone-beam
illumination, beyond the resolution limit given by the cone-beam numerical aperture. We therefore
refer to this approach as super-resolution in-line holography [1]. We demonstrate the improved
experimental capability by reconstruction of a test pattern with a field of view of 5×5 µm² and am² and a
resolution of 11 nm, using an illumination profile tailored by waveguide optics.
Secondly we demonstrate a new imaging scheme, to which we refer as reporter based imaging [2].
In this imaging scheme we use a multilayer zone plate (MZP) not as a focusing lens but as a
’reporting’ structure positioned in the near-field of the diffracted beam behind the sample. At first,
this configuration seems identical to a conventional transmission x-ray microscope or optical
microscope, but instead of recording a sharp image of the sample directly, we exploit the advantage
of the coherent illumination and of the propagation based phase contrast. This results in a better
image quality concerning both resolution and contrast compared to conventional transmission x-ray
microscopy. We demonstrate this new approach and obtain sub-10 nm spatial resolution.
[1] J. Soltau, M. Vassholz, M. Osterhoff and T.Salditt, In-line holography with hard x-rays at sub-15
nm resolution, Optica (2021), 8, 818-823
[2] Publication in preparation