Laser-Induced Transient Opacity in Helium Nanodroplets Probed by Single-Shot Coherent Diffraction

Single-shot coherent diffractive imaging with intense short-wavelength light pulses enables the structural characterization of individual nanoparticles in free flight with high spatial and temporal resolution. Conventional coherent diffractive imaging assumes that the target object exhibits a linear scattering response and static electronic properties. Here, we extend this approach to investigating transient-laser-driven modifications of the electronic structure in individual nanoparticles, imprinted in their time-resolved diffraction patterns. In the presence of a near-infrared laser pulse, we observe a pronounced reduction in the diffraction signal from helium nanodroplets when probed with ultrashort extreme ultraviolet pulses. This effect is attributed to a light-field-induced modification of the electronic structure of the droplets, which substantially increases their extreme ultraviolet absorption. Our results demonstrate the possibility to capture ultrafast light-driven electron dynamics in nanoscale systems with single-particle diffraction. This opens a pathway toward the spatiotemporal tracking of reversible changes in the electronic properties of nanoscale structures with potential applications in ultrafast x-ray optics, materials science, and all-optical signal processing.