Experimental investigation of high-gain Ne-like Ge soft-x-ray laser by double-massive-target coupling

By means of a novel experimental design called double-massive-target coupling, significant amplification of five lasing lines was observed with wavelengths (λ) of 19.6, 23.2, 23.6, 24.7, and 28.6 nm from 3p–3s transitions in Ne-like Ge ions at an irradiance of 1.2 × 1013 W/cm2 on the axis of an elongated plasma column. The maximum gain-length product (GL) values achieved were greater than 14 for 2 of the 5 lasing lines at 23.2 and 23.6 nm. Temporally resolved measurements of x-ray laser spectra indicate that the duration of the gain was ~0.8 ns, which is comparable with the Gaussian driving laser pulse width of 1 ns (FWHM) in our experiments. The measured divergence and refraction angles of the x-ray laser beam at 23.6 nm are presented. The dimension and position of the gain region are estimated.