Tabletop X-Ray Coherent Diffraction Imaging at the Nano-Femto-Limits

Figure: Laser-like, fully spatially coherent, high harmonic beams produce interferences patterns when used to illumunate a pair of Young’s Double Slits. These beams are ideal for x-ray coherent diffractive imaging.


The quest to understand structure, dynamics and function at the nanoscale continues to drive new ultrahigh-resolution imaging technologies. Rapid progress in the past five years has laid the foundation for revolutionary new optical microscopy technologies that combine coherent illumination with computer-aided image processing algorithms. X-ray imaging at the nanoscale is the most-recent technique to benefit from these new imaging modalities. Soft x-ray microscopy is a general-purpose nanoscale imaging technique that complements electron and IR/VIS/UV microscopies because it can penetrate thick (opaque) samples and achieve high spatial resolution, with the added advantage of elemental and chemical specificity. In the past, the spatial resolution of x-ray microscopes was limited to ≈ 15 nm because of the technical challenges of making zone plate lenses. Furthermore, the temporal resolution was limited by the long (ns-ps) pulse durations that could be generated in the x-ray region.
Recently however, both high harmonic generation and x-ray free electron lasers have made it possible to generate ultrafast coherent x-ray beams. When combined with new diffractive imaging techniques that essentially replace the imaging optics in a microscope with an iterative phase retrieval algorithm, wavelength-limited nano-imaging is possible. In x-ray coherent diffractive imaging (XCDI), an object is illuminated with a coherent beam of light, and the light scattered from the object is then recorded using a CCD detector. An iterative phase retrieval algorithm can recover an image from the scattered-light diffraction pattern, essentially replacing the objective lens with a computer algorithm.
In recent exciting work, we used bright 13 nm high harmonic beams to achieve a record 22 nm spatial resolution for any tabletop x-ray microscope using any imaging modality. We also demonstrated an ability to extract 3D information about the sample from a 2D scatter pattern. In the future, 3D XCDI will enable nanoscale dynamic imaging of thick samples, in 3D, with elemental and chemical specificity, inherent image contrast, and with simultaneously high spatial (sub-10nm) and temporal (1 – 100fs) resolution—all in a tabletop setup.

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