Digital in-line holography with photons and electrons

We review the status of digital in-line holography with numerical reconstruction. Its application in optics with a laser as a source of coherent radiation has been perfected in recent years with optimal resolution achievable on a routine basis in such diverse areas as three-dimensional mapping and tracking of micron-sized particle distributions, growth of polymer spherulite, and structural studies of cells and micro-organisms. Digital in-line holography with coherent low-energy electron beams from an atomic-sized field emitter tip has now achieved nanoscale resolution and can, according to theoretical simulations and estimates, achieve atomic resolution, one hopes in the near future.