Spectral control of beyond extreme ultraviolet emission from a dual-laser-produced plasma

We demonstrated spectral control of beyond extreme ultraviolet (B-EUV) emission at a central wavelength of 6.76 nm from a gadolinium (Gd) laser-produced plasma. The highest spectral purity (SP) was 5.1% under dual 1-μm laser pulse irradiation. It doubled compared to a value of 2.4% attained under single laser pulse irradiation of solid density Gd because of the reduction in optical depth. The highest maximum SP was higher than that obtained using a mid-infrared laser at 10.6 μm. The SP for the 150-ps main laser was also higher than that for 6-ns main laser irradiation. Our approach can be extended to mid-infrared solid-state laser-produced plasmas (LPPs) using driving laser wavelengths ranging from 2 to 9 μm for efficient B-EUV source development.