Target optimization of a water-window liquid-jet laser–plasma source

Abstract

We optimize the water-window x-ray flux and debris deposition for a liquid-jet laser plasma source by varying both the target diameter and the jet material. For two target liquids, methanol and ethanol, measurements of the λ=3.37 nm C VI x-ray flux and the debris deposition rates are presented as function of the jet diameter. It is shown that the effective carbon debris deposition is more than 1 order of magnitude smaller for methanol, while the x-ray flux is reduced only ∼40%. The reduction in carbon debris deposition may be explained by reactive ion etching by oxygen from the plasma. Thus, the methanol water-window source may be operated at a 5–10× higher flux without increasing the debris deposition. The optimization potentially allows a reduction of the exposure time of compact soft x-ray microscopy or other water-window applications based on such sources without increasing damage to sensitive x-ray optics.