1. University of California, Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, California 94550, USA
   
2. Center for Biophotonics Science and Technology, University of California, Davis, 2700 Stockton Boulevard, Suite 1400, Sacramento, California 95817, USA
   
3. Stanford Synchrotron Radiation Laboratory, Stanford Linear Accelerator Center, 2575 Sand Hill Road, Menlo Park, California 94305, USA
   
4. Laboratory of Molecular Biophysics, Department of Cell and Molecular Biology, Uppsala University, Husargatan 3, Box 596, SE-75124 Uppsala, Sweden
   
5. Institut für Optik und Atomare Physik, Technische Universität Berlin, Hardenbergstrae 36, PN 3-1, 10623 Berlin, Germany
   
6. Deutsches Elektronen-Synchrotron, DESY, Notkestrae 85, D-22607 Hamburg, Germany
   
7. Present address: Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA (S.M., D.A.S.).

Correspondence to: Henry N. Chapman^1,2 Correspondence and requests for materials should be addressed to H.N.C. (Email: henry.chapman@llnl.gov).

Extremely intense and ultrafast X-ray pulses from free-electron lasers offer unique opportunities to study fundamental aspects of complex transient phenomena in materials. Ultrafast time-resolved methods usually require highly synchronized pulses to initiate a transition and then probe it after a precisely defined time delay. In the X-ray regime, these methods are challenging because they require complex optical systems and diagnostics. Here we propose and apply a simple holographic measurement scheme, inspired by Newton's 'dusty mirror' experiment¹, to monitor the X-ray-induced explosion of microscopic objects. The sample is placed near an X-ray mirror; after the pulse traverses the sample, triggering the reaction, it is reflected back onto the sample by the mirror to probe this reaction. The delay is encoded in the resulting diffraction pattern to an accuracy of one femtosecond, and the structural change is holographically recorded with high resolution. We apply the technique to monitor the dynamics of polystyrene spheres in intense free-electron-laser pulses, and observe an explosion occurring well after the initial pulse. Our results support the notion that X-ray flash imaging^{2, 3} can be used to achieve high resolution, beyond radiation damage limits for biological samples⁴. With upcoming ultrafast X-ray sources we will be able to explore the three-dimensional dynamics of materials at the timescale of atomic motion.