Broadband coherent diffractive imaging Recent advances in attosecond science VUV free-electron lasers [2] with /home/webapps/asp_fr/data/asp/publications/synchrotron-soleil/synchrotron-soleil-2020/soleil-highlights-2020-hd-ss-tc0.5%, bandwidths allow raise the demand for ultrafast imaging CDI convergence [3]. However, performing CDI with current attosecond pulses poses a real challenge due to their extremely methods for tracking different processes at broad ≥10% spectra. Here we present a novel method that the shortest space and time scales. However, allows to overcome the blurring of coherent diffractive patterns such methods combining nanometre spatial due to the broadband illumination and to perform phase retrieval of a single broadband diffraction pattern. This opens the way resolutions with the extremely broad nature towards single-shot attosecond flash imaging, as is shown by of attosecond spectra are still lacking. the experimental validation in the visible and hard X-ray range. Here, we present an approach that enables NUMERICAL MONOCHROMATIZATION nanometre spatial resolution coherent diffractive imaging, an up-to-now quasi- In a conventional CDI experiment, the sample is reconstructed by the use of an iterative phase retrieval algorithm, which iterates monochromatic method, to be applied with between the measured diffraction pattern and the sample broadband illumination. Proof of principle plane—with constraints on typically the isolation of the object in tests validated the method in the visible and real space—to converge to the solution. For the broadband case we introduced a numerical monochromatization step before the hard X-ray ranges. Moreover, the generality iterative process. As the broadband diffraction pattern is given and easy implementation of this method is by the incoherent superposition of monochromatic diffraction expected to result in widespread applications, patterns weighted by the spectrum of the diffracted radiation, the retrieval of the monochromatic pattern is reduced to a such as synchrotron pink beam coherent linear inverse problem. The proposed method, based on this diffraction imaging. mathematical inversion, depends solely on the knowledge of the energy spectrum of the incident illumination. It can be used Coherent diffractive imaging (CDI) is a powerful single-shot with standard phase retrieval algorithms, as shown here, or femtosecond nanoscale imaging technique [1].It is based on integrated as a module in algorithms for other types of lensless solving the so-called phase problem using a phase retrieval imaging (holography, ptychography) to allow them to cope with algorithm and thus the achievable best spatial resolution is onlybroadband sources. limited by the wavelength. CDI is based on the fundamental assumption of spatial and temporal coherence, the latter EXPERIMENTAL VALIDATION imposing the quasi-monochromaticity of the illumination. In BROADBAND VISIBLE-LIGHT ILLUMINATION practice, successful phase retrieval can be obtained for finiteA gold-coated silicon nitride membrane sample with etched features bandwidth illumination. For example, soft X-ray femtosecond (Fig. 1.e), was sequentially exposed to narrow (Δλ/λ = 1.2%) pulses from table-top high-harmonic generation (HHG) and and broadband (Δλ/λ = 11%) visible light femtosecond beams FIGURE 1 86