High Harmonic Generation (HHG)
High harmonic generation (HHG) is a laser-driven process which allows for creating extreme-UV and X-ray radiation while preserving the high quality of the laser beam. In our lab, we employ HHG as a source for lensless microscopy, where nanoscale images of investigated samples are retrieved from scattering diffraction signals via a computer algorithm, without the need for optical elements.
We employ a two-color generation scheme to control the polarization state of the emitted harmonics [Kfir et al., Appl. Phys. Lett. 108 (2016) ] and thus can investigate chiral systems or magnetic materials via x-ray magnetic circular dichroism (XMCD).
Recently, we demonstrated the first magnetic imaging using high-harmonic radiation [Kfir et al., 2017]. By employing an advanced detection scheme for weak scattering signals, we are currently reaching sub-20 nm spatial resolution, below the illuminating wavelength. Our combination of dichroic imaging with holographically-enhanced diffractive imaging allows us to extract the small dichroic signals independently from waveguiding effects in the sample [Zayko et al., 2016; Kfir et al., 2017]. With this approach, we reach spatial resolutions and image qualities competitive to those obtained at large-scale facilities such as synchrotrons, free-electron lasers for much shorter wavelengths.
This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 752533