Broadband holography-assisted coherent imaging -- towards attosecond imaging at the nanoscale

In recent years nanoscale coherent imaging has emerged as an indispensable imaging modality allowing to surpass the resolution limit given by classical imaging optics. At the same time, attosecond science has experienced enormous progress and has revealed the ultrafast dynamics in atoms, molecules, and complex materials. Combining attosecond temporal resolution of pump-probe experiments with nanometer spatial resolution would allow studying ultrafast dynamics on the smallest spatio-temporal scales but has not been demonstrated yet. Unfortunately, the large bandwidth of attosecond pulses usually hinders high-resolution coherent imaging. Here we present a robust holography-enhanced coherent imaging method, which allows combining high quality and high spatial resolution coherent imaging with a large spectral bandwidth. By implementing our method at a high harmonic source we demonstrate, for the first time, a spatial resolution of 34 nm (2.5 {\lambda}) in combination with a spectral bandwidth supporting a Fourier limited pulse duration of only 380 as. The method is single-shot capable, additionally retrieves the spectrum from the measured diffraction pattern, and is thus immune against shot-to-shot fluctuations. This paves the way for an ultrafast view on nanoscale dynamics e.g. ultrafast charge transfer or ultrafast spin currents being relevant for Petahertz electronics and future data storage.