Dose constraints for high-resolution imaging of biological specimens with extreme ultraviolet and soft X-ray radiation

We present a theoretical evaluation of radiation dose constraints for extreme ultraviolet (EUV) and soft X-ray microscopy. Our work particularly addresses the long-standing concern regarding strong absorption of EUV radiation in biological specimens. Using an established dose-resolution model, we compare hydrated and dehydrated cellular states and quantify the fluence required for nanoscale imaging. Our analysis identifies a protein window spanning photon energies from ∼70 eV up to the carbon K-edge (284 eV). Towards the upper end of this range, at photon energies above 100 eV, EUV microscopy could in principle achieve sub-10 nm half-pitch resolution in dehydrated samples at doses well below the Henderson limit. In this situation, the radiation dose required for EUV imaging is predicted to be substantially lower than what is required for comparable resolution in water window soft X-ray microscopy. Furthermore, EUV photons with sufficiently high energy exhibit penetration depths of µm-level in dehydrated biomatter, enabling exceptional amplitude and phase contrast through thin cellular regions and small cells. These findings provide quantitative guidelines for photon energy selection and support the EUV protein window as a dose-favorable and physically viable modality for high-resolution, label-free, material-specific imaging of dehydrated biological matter.