Single shot 3D imaging using free electron laser radiation

The ability to perceive the three-dimensional (3D) structure of objects is integral to our everyday interaction with the world. In microscopy this ability has profound implications, which can be profitably exploited in several fields, ranging from materials science to medical diagnostics. Traditionally, 3D X-ray microscopy is achieved at synchrotrons using tomographic techniques, where multiple images of an object are collected from different angles and then combined to create a 3D rendering of the sample. However, this method is intrinsically time-consuming and the need to acquire multiple views limits our ability to capture rapid dynamical processes, confining the application of 3D X-ray imaging to static studies.

In a recent breakthrough, we have developed a new way to capture 3D information by an isolated object using ultrashort and ultrabright flashes of extreme ultraviolet (EUV) radiation generated by a free electron laser (FEL). The experiment has been carried out at the DiProI beamline, the end-station of the FERMI FEL dedicated to dynamical coherent and diffraction imaging. Novel data analysis algorithms were developed in collaboration with the Scientific Computing Team (SciComp). In our approach, instead of acquiring multiple serial images from different view angles, two “twin” EUV pulses simultaneously hit the object (Figure 1b) from different directions. This instantaneous illumination led to two diffraction patterns (Figures 1a and 1c) containing the light scattered by the object and by reference structures (i.e., pinholes and a slit) purposely realized into the sample. This permitted to straightforwardly obtain holographic images of the sample from the two different view angles; see Figures 1d and 1e. This information is then used as an input guess for a coherent diffraction imaging (CDI) reconstruction, which finally provides us with two independent and high resolution (sub-100 nm) bidimensional images of the sample from the two view angles; see Figure 1f and 1g. By combining these images in an ad-hoc developed algorithm, based on ray tracing and on the physical constraints of the illumination geometry, we were able to retrieve 3D stereoscopic rendering of various objects. An example is reported in Figure 1h, corresponding to the sample shown in Figure 1b. An interactive version of the Table of Contents graphics shown in homepage is avaialble here.

Figure 1: panels a) and c) are the diffraction patterns from the object shown in panel b), simultaneously collected at 0° and 40° view angles; the image in panel b) was obtained by scanning electron microscopy. Panels d) and e) are the holographic reconstruction of the sample and reference slit; see the red circle and the red rectangle in panel d). Such holograms are thus used to yield the CDI reconstructed images depicted in panels f) and g). Panel h) displays the 3D reconstruction of the sample shown in panel b).

The developed approach is very similar to how our eyes work in tandem to provide depth perception. The investigated objects were specifically designed to facilitate this demonstrative experiment, but their dimension and fine details represent typical 3D structures that we might encounter in real life, like tiny magnetic memories used in hard disc or biological samples. What's exciting is that this approach provides very fine details, down to about 100 nm, which is smaller than most bacteria. The visualization of the 3D structure at such tiny scales is also crucial for improving micro-devices and batteries. Most importantly, the 3D image can be collected within a single FEL laser pulse, allowing us to capture even very fast events (the FEL pulse duration is as short as a few 10s of fs), possibly circumventing the issue of radiation damage.

This result paves the way for time-domain 3D imaging, meeting the demands of capturing quickly evolving structural changes within individual 3D objects, like in chemical reactions, biological processes and phase transitions. Such processes can be triggered by an ultrafast optical pulse, whose integration in this setup is already available. The potential of the technique also encompasses higher photon energies, accommodating broader spectral ranges and enabling the incorporation of multiple viewing angles through a more complex optical setup. This could bring us closer to capturing the finer details of our world in a way that was not possible before.

This research was conducted by the following research team:

Danny Fainozzi^1,†, Matteo Ippoliti^1,†, Fulvio Bille¹, Dario De Angelis¹, Laura Foglia¹, Claudio Masciovecchio¹, Riccardo Mincigrucci¹, Matteo Pancaldi¹, Emanuele Pedersoli¹, Christian M. Günther², Bastian Pfau³, Michael Schneider³, Clemens Von Korff Schmising³, Stefan Eisebitt^3,4, George Kourousias¹, Filippo Bencivenga¹, and Flavio Capotondi^1
1 Elettra - Sincrotrone Trieste S.C.p.A., Trieste, Italy
² Technische Universität Berlin, Zentraleinrichtung Elektronenmikroskopie (ZELMI), Berlin, Germany
³ Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie, Berlin, Germany
⁴ Technische Universität Berlin, Institut für Optik und Atomare Physik, Berlin, Germany
^† These authors contributed equally to this work

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