Femtosecond time-delay X-ray holography

Dusting off an old technique Inspired by the 'dusty mirror' experiment that Isaac Newton used to demonstrate interference, Chapman et al . have devised a scheme to study microscopic particles with ultrafast and intense X-ray pulses. Newton's experiment involved visible light scattering from dust particles on the front of a back-quicksilvered mirror twice (once going into the mirror, once on its way out), and the corresponding circular interference patterns. In the modern version, X-ray pulses are focused on a thin membrane with polystyrene particles placed in front of an X-ray mirror. A pulse passes through the sample, triggering the explosion of a particle, and is then reflected back on to the sample by the mirror. The resulting diffraction pattern contains accurate time and spatially resolved information about the exploding particles. This type of X-ray 'flash' imaging may be used to explore the three-dimensional dynamics of materials at the timescale of atomic motion. A modern version of Newton's 'dusty 'mirror' experiment is made, whereby X-ray pulses are focused on a thin membrane with polystyrene particles placed in front of an X-ray mirror. After a pulse traverses through the sample, triggering the explosion of a particle, it is reflected back on to the sample by the mirror to probe this reaction. The resulting diffraction pattern contains accurate time and spatially resolved information about the exploding particles. 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’ experiment 1 , 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 intens