Optical coherence tomography with nanoscale resolution using a laser-driven high-harmonic source

The use of extreme ultraviolet (XUV) radiation for nanoscale imaging has dis-tinctive advantages: It is label-free, facilitates high contrast, allows material identification and penetrates opaque matter. Recent advances in the laser-based generation of high-flux XUV radiation render this imaging modality accessible to a growing number of users. At the same time, unique prop-erties such as ultrafast temporal resolution attract the interest of more and more scientists. On the other hand, there are challenges: Laser-based XUV radiation usually has broad spectra while XUV imaging regularly calls for monochromatic radiation. In addition, cross-sectional imaging is a challenge. Here we report on the first demonstration of XUV coherence tomography(XCT) with a broadband high-harmonic source and show that XCT with nanometer depth resolution is feasible and represents a highly sensitive non-invasive cross-sectional imaging method that efficiently exploits broadband XUV radiation. A three-step phase retrieval algorithm allows using simple experimental schemes while eliminating artifacts.