The paper on EUV wafer metrology using the computational imaging method “ptychography” has been selected by Nature Light: Science & Applications as the cover article for the issue published on 31 October 2024.
The cover picture shows a photo of the high-harmonic generation (HHG) process in the compact tabletop EUV source. In this photo, the researchers look into the HHG vacuum vessel from a window on the top. The drive IR pulse laser (propagating from left to right) is focused on a pressurized Argon gas jet between a gas nozzle and a gas catcher (placed along the vertical direction).
The bright white plasma generates higher harmonics in the 10-20 nm wavelength range. The colourful glow and streak, registered as purple-pink by the camera, originate from the scattered IR light.