Extending single attosecond pulse technology from currently sub-200 eV to the so called 'water window' spectral range may enable for the first time the unique investigation of ultrafast electronic processes within the core states of bio-molecules as proteins or other organic materials. Aperiodic multilayer mirrors serve as key components to shape these attosecond pulses with a high degree of freedom and enable tailored short pulse pump-probe experiments. Here, we report on chirped CrSc multilayer mirrors, fabricated by ion beam deposition with sub-angstrom precision, designed for attosecond pulse shaping in the 'water window' spectral range.

Recent advances in the development of attosecond soft X-ray sources ranging into the water window spectral range, between the 1s states of carbon and oxygen (284 eV-543 eV), are also driving the development of suited broadband multilayer optics for steering and shaping attosecond pulses. The relatively low intensity of current High Harmonic Generation (HHG) soft X-ray sources calls for an efficient use of photons, thus the development of low-loss multilayer optics is of uttermost importance. Here, we report about the realization of broadband Cr/Sc attosecond multilayer mirrors with nearly atomically smooth interfaces by an optimized ion beam deposition and assisted interface polishing process. This yields to our knowledge highest multilayer mirror reflectivity at 300 eV near normal incidence. The results are verified by transmission electron microscopy (TEM) and soft/hard X-ray reflectometry.

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Recent advances in the development of attosecond soft X-ray sources ranging into the 'water window' spectral range, between the carbon 1s and oxygen 1s states (284 eV -543 eV), are also driving the development of suited broadband multilayer optics for attosecond beam steering and dispersion management. The relatively low intensity of current High Harmonic Generation (HHG) soft X-ray sources calls for an efficient use of photons, thus the development of low-loss multilayer optics is of uttermost importance. Here, we report about the realization of atomically smooth interfaces in broadband CrSc multilayer mirrors by an optimized ion beam deposition and assisted interface polishing process.