In Brief
Fastest Film of the World Recorded
Chemical and biological reactions take place with such speed that so far they could not be recorded in real time. A "molecular film" illustrating how a molecule behaves at the most important moment of a chemical reaction would help to better understand fundamental processes in the natural sciences. Such processes often last only a few femtoseconds. This time frame allows for capturing one image by way of an ultra-short light flash – but not several images. The images would superimpose each other on the detector reproducing the image and thus produce a washy effect. Even if one was to exchange the detector alternating between two images with the speed of light, the process would take too long.
In spite of these difficulties, the joint research group "Functional Nanomaterials" of the HZB and the Technical University Berlin at the Free-Electron Laser of DESY Hamburg managed to capture such ultra-fast image sequences of objects in the micrometre range using X-ray laser pulses. The researchers developed an elegant idea as to how to decipher the superimposed images: An X-ray hologram serving as detector allows to capture two images at the same time. To obtain the final image sequence, several steps are necessary: First the scientists divide individual bundles of rays from an X-ray laser beam into two separate light pulses. They force one of these light pulses to take a small detour, thus causing the two light pulses to hit the object they intend to capture with a minimal delay in time. This results in two holograms. On the basis of these, both images can be reconstructed using a mathematical function. In doing so, the position of the reconstructed images relative to the depicted object is different and depends on which laser beam created them. The researchers simply allocate the images to the respective light pulses and thereby obtain the chronological correct sequence of images. "The long-term goal is to be able to follow the movement of molecules and nanostructures in real time", says project manager Prof. Dr Stefan Eisebitt. The extremely high temporal resolution coupled with the possibility of seeing the tiniest of objects was the motivation behind developing the procedure.
