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In this paper we examine the behavior of small cluster of atoms in a short (10-50 fs) very intense hard x-ray (10 keV) pulse. We use numerical modeling based on the non-relativistic classical equation of motion. Quantum processes are taken into account by the respective cross sections. We show that there is a Coulomb explosion, which has a different dynamics than one finds in classical laser driven cluster explosions. We discuss the consequences of our results to single molecule imaging by the free electron laser pulses.

The possibility of atomic-resolution X-ray holography is analysed. Based on numerical model calculations we show that direct threedimensional (3D) imaging of atoms is feasible by holographic reconstruction. The connection between the Kossel line pattern and the X-ray hologram of atoms in a single crystal is discussed.

A review of holographic methods using hard x-rays is presented. The main emphasis is put on those techniques which aim to produce atomic resolution. For this reason 'the inside source concept' and its experimental realizations are discussed in detail. Apart from the general description of holographic imaging with atomic resolution, specific features such as the effect of multiple scattering, translation periodicity and angular dependence of the atomic scattering factor are also given.

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The short and intense pulses of the new X-ray free electron lasers, now operational or under construction, may make possible diffraction experiments on single molecule-sized objects with high resolution, before radiation damage destroys the sample. In a single molecule imaging (SMI) experiment thousands of diffraction patterns of single molecules with random orientations are recorded. One of the most challenging problems of SMI is how to assemble these noisy patterns of unknown orientations into a consistent single set of diffraction data. Here we present a new method which can solve the orientation problem of SMI efficiently even for large biological molecules and in the presence of noise. We show on simulated diffraction patterns of a large protein molecule, how the orientations of the patterns can be found and the structure to atomic resolution can be solved. The concept of our algorithm could be also applied to experiments where images of an object are recorded in unknown orientations and/or positions like in cryoEM or tomography.