Speaker
Description
Recent advances in ultrafast laser technology have facilitated the development of high-brightness, high-order harmonic generation (HHG) sources. These compact tabletop systems now enable high-resolution coherent diffractive imaging (CDI) experiments previously restricted to large-scale facilities [1, 2]. To date, HHG-based imaging has been largely confined to the EUV spectral range (<100 eV), as these sources often lack sufficient brightness and stability in the soft X-ray regime (>100 eV). However, numerous applications would benefit from soft X-ray radiation, including the imaging of biological samples in their natural aqueous environments (the "water window", 280–530 eV) and the investigation of magnetic materials at L-edges (∼700 eV).
In this contribution, we demonstrate what is, to our knowledge, the first soft X-ray ptychography measurements acquired using a high-harmonic generation (HHG) source at 185 eV photon energy. These results are enabled with a custom-engineered, ultrahigh-stability infrared laser system [3]. Operating at a central wavelength of 1.58 μm, this driver facilitates uninterrupted, 24/7 generation of soft X-ray harmonics. When driven in helium, the source produces a broadband X-ray continuum spanning from 150 eV to beyond 350 eV. Multilayer mirrors are typically used to select a narrow bandwidth (~1%) from the broadband continuum to meet the temporal coherence requirements of coherent diffractive imaging. However, this approach leaves the majority of generated soft X-ray photons unused and, therefore, leads to long exposure times for soft X-ray imaging. To address this, we have developed strategies to utilize a significantly broader spectral bandwidth, thereby maximizing usable photon flux. In a proof-of-concept experiment at 92 eV, we demonstrate broadband ptychography with 10% bandwidth without significant degradation of spatial resolution. Applying this approach to the soft X-ray regime offers a substantial increase in photon flux, promising sub-100 nm spatial resolution for biological specimens within the water window.
[1] R. Sandberg et al., Phys. Rev. Lett. 99, 098103 (2007)
[2] M. Seaberg et al., Optica 1, (2014)
[3] D. Morrill, et al., APL Photonics 1 2025; 10 (11): 116101