Unlike traditional outside-source holography

X-ray fluorescence holography is carried out with fluorescent atoms in a sample as source light for holographic imaging. With the method

three-dimensional arrangement of atoms into crystals can be observed obviously. However

just like traditional outside-source holography

X-ray fluorescence holography suffers from the inherent twin-image problem

too. With a 27-Fe-atoms cubic lattice as model

we discuss in this paper influence of the photon energy of incident source in removing twin images in reconstructed atomic images by numerical simulation and reconstruction with two-energy X-ray fluorescence holography. The results indicate that incident X-rays of nearer energies have better effect of removing twin images. In the detector of X-ray holography

minimum difference of the two incident energies depends on energy resolution of the monochromator and detector

and for inside source X-ray holography

minimum difference of the two incident energies depends on difference of two neighboring fluorescent energies emitting from the element and energy resolution of detector. The spatial resolution of atomic images increases with the incident energies. This is important for experiments of X-ray fluorescence holography

which is being developed on Shanghai Synchrotron Radiation Facility.