Enhancement of 6.7 nm EUV emission from laser-produced Gd plasma with micro-structured target

We present the experimental investigations of extreme ultraviolet (EUV) radiation of laser-produced plasma based on the micro-structured Gd target and obtain a strong EUV radiation intensity at the wavelength of 6.7 nm. The intensive extreme ultraviolet radiation and narrow-band spectra are achieved by laser irradiation in the groove position of the target. The spectral widths from the micro-structured target are approximately two-thirds width of that of the flat target, and the EUV intensity enhancement ratio is 1.48 comparing with that of the flat case. The measurements of the electron density of Gd plasma were performed using Nomarski interferometry. The results show that the plasma generated by the micro-structured Gd target is confined by the groove between the micro-columns. The plasma electron density distribution is mainly concentrated in the laser incidence direction and the density is higher than that of planar target. Finally, the parameters of the groove width of structured target and laser energy are varied to enhance the EUV radiation. This study shows that the confinement effect of the structured target can improve the extreme ultraviolet radiation. Those findings are expected to provide new approaches in developing the next-generation extreme ultraviolet light source.