Parametric optimization of a narrow-band 13.5-nm emission from a Li-based liquid-jet target using dual nano-second laser pulses

We demonstrate the applicability of a Li-based liquid jet as a regenerative source of narrow-band extreme-ultraviolet (EUV) emission at 13.5 nm. It was found that a conventionally used single laser pulse did not produce optimum plasma conditions for a low-Z target, like Li. It was shown that deployment of dual nano-second laser pulses enhanced the in-band EUV conversion efficiency (CE) at 13.5 nm in 2 sr by three times its value using a single laser pulse. Dependence of the emission spectra and EUV CE on the delay time between dual laser pulses revealed that the emission at 13.5 nm from Li ions was preferably enhanced at a lower plasma temperature compared to that at 13.0 nm from oxygen ions.