Speaker
Dr
Taisia Gorkhover
(University of Hamburg)
Description
The adventvent of X-ray Free Electron Lasers (FELs) opens the door for unprecedented studies on non-crystallin nanoparticles with high spatial and temporal resolutions [1]. In the recent past, ultrafast X-ray imaging studies have elucidated hidden processes in individual fragile specimens, which are inaccessible with conventional imaging techniques. Examples include airborne soot particle formation [2], metastable states in the synthesis of metal nonaparticles [3], transient vortexes in superfluid quantum systems [4] and non-equilibrium dynamics of laser-superheated nanoparticles [5].
Theoretically, ultrafast coherent diffraction X-ray imaging (CDI) might achieve sub-nanometer resolution in combination with sub-femtosecond temporal precision. The best demonstrated spatial resolution of ultrafast X-ray CDI is still far away from the diffraction limit due to restrictions in X-ray scattering signal strength. The brightness of the diffraction patterns is determined by a combination of several factors such as X-ray photon flux, image imperfections and ultimately, sample damage [6,7]. Ionization through the FEL pulse during the exposure is generally considered detrimental to the quality of single shot images. In general, ionization can lead to increased transparency of the sample and even modify the structure of the sample during the imaging process.
In contrast, our study conducted at the Linac Coherent Light Source (LCLS) indicates that ionization might increase the brightness of the diffraction image prior to significant structural damage if the pulses are very short. In our experiment we observe that the X-ray coherent scattering cross section of Xe nanoparticles increases significantly above the 3d absorption edge for X-ray pulses as short as 0.5 - 10 fs.
A Monte-Carlo-simulation [8] attributes the observed increase to transient ionic resonances, which are created through X-ray absorption and subsequent electronic damage during the FEL exposure. If the FEL pulses are shorter than few femtoseconds, the electronic damage does not affect the ionic structure. Using the novel XLEAP mode at LCLS [9], we have demonstrated that it is possible to image individual nanoparticles with few nanometer and sub-fs temporal resolutions. Our model also suggests that transient ionic resonances can be exploited with intense sub-fs short pulses even for lighter elements. Overall transient resonances provide a novel avenue in improving the quality of images of in CDI.
[1] Neutze, Richard, et al. Nature 406.6797 (2000): 752-757
[2] Loh, N. D. et al. Nature 486, 513–517 (2012).
[3] Barke, I. et al. Nat. Commun. 6, (2015):6187.
[4] Gomez, L. F. et al. Science 345, 906–909 (2014).
[5] Gorkhover,T. et al. Nat. Phot. 10, (2016):93.
[6] Aquila, Andrew, et al. Structur. Dyn. 2.4
(2015).: 041701
[7] Ho, Phay J., et al. Nat. Commun 11 (2020).
[8] Ho, Phay J., et al. Phys. Rev A 94, no. 6 (2016): 063823.
[9] Duris, Joseph, et al. Nat. Phot. 14.1 (2020): 30-36.
Primary author
Dr
Taisia Gorkhover
(University of Hamburg)
