We experimentally study the morphology of a radially expanding sheet of liquid tin, formed by nanosecond-pulse Nd:YAG laser impact on a spherical microdroplet. Specifically, the sheet thickness profile and its time evolution are captured in detail over a range of laser-pulse energies and for two droplet sizes. Two complementary methods to determine this thickness are employed and shown to be in excellent agreement. All obtained thickness profiles collapse onto a single self-similar curve. Spatial integration of the thickness profiles allows determining the volume of the sheet. Remarkably, less than half of the initial amount of tin remains in the sheet under conditions relevant for industrial sources of extreme ultraviolet light, where these thin tin sheets serve as target material. Further analysis shows that the dominant fraction of the mass lost from the sheet during its expansion ends up as fine fragments. We propose that such mass loss can be minimized by producing the sheet targets on the shortest possible timescale. These findings are particularly valuable for ongoing developments in state-of-the-art nanolithography.

Phys. Rev. Appl.
EUV Plasma Processes

Liu, B., Kurilovich, D., Gelderblom, H., & Versolato, O. (2020). Mass loss from a stretching semitransparent sheet of liquid tin. Phys. Rev. Appl., 13(2), 024035: 1–10. doi:10.1103/PhysRevApplied.13.024035