Holographic methods as local probes of the atomic order in solids

In the last 15 years, several techniques based on the holographic principle have been developed for the study of the 3D local order in solids. These methods use various particles: electrons, hard X-ray photons, gamma photons, or neutrons to image the atoms. Although the practical realisation of the various imaging experiments is very different, there is a common thread; the use of inside reference points for holographic imaging. In this paper, we outline the basics of atomic resolution holography using inside reference points, with particular emphasis on the hard X-ray case. Furthermore, we outline the experimental requirements and what has been practically realized in the last decade. Lastly, we give examples of applications and future perspectives.