Parallelization of Atomic Image Reconstruction from Holograms
209
4. reconstruction of atomic images and
5. display of them
Because it is known that low frequency noise called background wave is included
in hologram data obtained by XFH experiments, the noise is removed before
reconstruction.
In the experiment, the intensity of X-ray fluorescence emitted from sample is
measured, while it is slanted from θ = 0 to 75 ◦ and rotated from φ = 0 to 360 ◦ at
each θ in Fig. 1. For θ > 75 ◦ , the meaningful intensity is not measured because
the surface of the sample and the incident X-ray are nearly parallel. By making use
of symmetry of crystal structure of the sample, the hologram data on the sphere
ranging from θ = 0 to 180 ◦ are completed. An example of hologram on the sphere
shown in Fig. 3 is obtained by their pre-processes such as removal of background
waves and completion of sphere data.
The values on grid points of the reconstructed atomic images are merely
values proportional to existence probability of atom at each grid point on the xy-z rectangular coordinate system. For a grid point, the value of low existence
probability is noise and its atom image is not displayed if the value is less than
threshold value and reconstructed images are displayed as shown in Fig. 4.
Fig. 3 An example hologram obtained by an experiment
209
4. reconstruction of atomic images and
5. display of them
Because it is known that low frequency noise called background wave is included
in hologram data obtained by XFH experiments, the noise is removed before
reconstruction.
In the experiment, the intensity of X-ray fluorescence emitted from sample is
measured, while it is slanted from θ = 0 to 75 ◦ and rotated from φ = 0 to 360 ◦ at
each θ in Fig. 1. For θ > 75 ◦ , the meaningful intensity is not measured because
the surface of the sample and the incident X-ray are nearly parallel. By making use
of symmetry of crystal structure of the sample, the hologram data on the sphere
ranging from θ = 0 to 180 ◦ are completed. An example of hologram on the sphere
shown in Fig. 3 is obtained by their pre-processes such as removal of background
waves and completion of sphere data.
The values on grid points of the reconstructed atomic images are merely
values proportional to existence probability of atom at each grid point on the xy-z rectangular coordinate system. For a grid point, the value of low existence
probability is noise and its atom image is not displayed if the value is less than
threshold value and reconstructed images are displayed as shown in Fig. 4.
Fig. 3 An example hologram obtained by an experiment