Coherent diffractive imaging (CDI) with x-ray free-electron laser (XFEL) pulses holds the promise to probe the structure and follow the dynamics of entities with atomic resolution. Despite continuous progress, it has remained a challenge to achieve nanometer resolution and elemental contrast with CDI due to sample damage. To circumvent these challenges, new XFEL imaging modalities are being developed for Single Particle Imaging (SPI). Recently, single-shot fluorescence intensity correlation (FIC) was proposed to measure the 3-D distribution of fluorescence emitting heavy elements excited by intense x-ray pulses. I will discuss the feasibility of using FIC for single particle imaging with intense XFEL pulses. I will present the results of fluorescence dynamics of non-periodic systems subject to femtosecon (fs) and XFEL pulses over a range of x-ray pulse parameters. Our approach is the Monte-Carlo/Molecular-Dynamics (MC/MD) method, which can account for the time-dependent transient electronic dynamics and structural modification of nanosized systems during and after the pulse. Using MC/MD method, we investigated the effectiveness of the FIC [P. J. Ho, et. al., Phys. Rev. A <b>101</b>, 043413 (2020); Structural Dynamics <b>8</b>, 044101 (2021)] for achieving high spatial resolution and elemental contrast in Ar clusters and Mo-doped iron oxide nanoparticles (NPs) with intense, fs and sub-fs XFEL pulses. We showed that the temporal emission profiles, as well as the FICs, depend strongly on the XFEL pulse duration, suggesting that the pulse duration can serve as a control knob to optimize FIC imaging. We found that few-fs pulses may be sufficient for achieving high-resolution information with FIC. More interestingly, we showed that the FICs from La of Mo illuminate the Mo distribution in Mo-doped iron oxide NPs (see Fig. 1).

Fluorescence intensity correlation imaging of single nanosized particles with intense X-ray pulses

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