Extreme Ultraviolet Emission from Laser-Irradiated Low-Density Xe Targets

The effect of the initial density of xenon (Xe) targets on extreme ultraviolet (EUV) emission has been investigated. With decreasing initial density, it was found that the spectral width around 11 nm becomes broad, and the intensity of 13.5 nm emission increases. The maximum conversion efficiency (CE) for solid Xe targets is approximately 0.6% at a 2×10 11 W/cm 2 of laser intensity, whereas that for the low-density targets is approximately 0.7% at a 4×10 11 W/cm 2 . The spectral broadening with decreasing initial density can be attributed to the change in optical thickness of laser-produced plasmas. The enhancement of CE is attributed to optically thick plasma formation.