# Influence of Pre-Ionized Plasma on the Dynamics of a Tin Laser-Triggered Discharge-Plasma
## 4 Experimental Results and Discussion  
Time-integrated tin EUV emissions are presented in Figure 5 under different laser-current delays. The energy and focal-spot diameter of the laser is fixed. Moreover, the discharge current is basically unchanged under different delays when the voltage is maintained. In this way, the input electrical energy is almost the same. Since the experimental spectrum is time-integrated over the laser pulse duration, it is not possible to characterize the emission by a single electron temperature over a range of power densities and electron temperatures. Figure 6 shows the comparisons with the theoretical simulations for steady-state electron temperatures 32, 20, and 12 eV, respectively. The fractions of the contributing ion stages for each electron temperature are given in the inset. It can be found that the theoretical result from the temperature of 32 eV fits the short-wavelength spectra well, especially between 13.0 and 13.5 nm. The long-wavelength spectra are in good agreement with those of the temperature of 12 eV when the delay is 1.5 us. In this way, the electron temperature of the plasma should be in the range of 12 and 32 eV during the Z-pinch process. According to Figures 3A and 6a, the spectra between 13 and 14 nm mainly originate from Sn\({}^{10+}\) and Sn\({}^{12+}\), and these ions mainly exist under the electron temperature 32 eV. In this way, the experimental data and the simulation data can agree well. The condition for Figure 6c is for the same reason. However, it can be seen from Figure 3A that the origin of spectra in the range of 14-15 nm is particularly complex, which are mainly coming from Sn\({}^{6+}\)-Sn\({}^{13+}\) ions. These ions can exist in a very large temperature range. At the same time, the measured spectrum is a time integral spectrum, which corresponds to the overall situation of plasma radiation spectrum at different temperatures during the whole Z-pinch process. This means that the spectra in this band can not match the fitting spectra at a certain temperature, which is also the main reason why the theoretical and experimental spectra in Figure 6b cannot fit well. According to Figures 5 and 6a, the intensity between 13 and 14 nm, which mainly originates from Sn\({}^{10+}\) and Sn\({}^{12+}\), is increasing with the delay from 0.7 to 5.0 us. Meanwhile, as shown in Figure 6b,c, there is some emission from the lower ion-stages, and the strongest emission is from Sn\({}^{6+}\) to Sn\({}^{9+}\) (14-16 nm). As shown in Figure 5b, the fraction of the emission between 14 nm and 16 nm is going down with the increase of the delay. As mentioned, the experimental spectra are time-integrated, which indicates average charge state during the plasma lifetime. In this way, the charge state increases with the delay, which means that the average electron temperature of the plasma is increasing. As the delay increases, the density of the plasma decreases due to expanding. In this way, the Z-pinch process gets more intense according to the Bennett equilibrium. The electron temperature gets higher as well. Moreover, there is a small peak around 12.5 nm, which is generated by the Sn\({}^{7+}\) 4d-5f transition. It almost cannot be detected when the delay is larger than 3.0 us according to Figure 5, which implies that the ratio of the ion stages lower than Sn\({}^{7+}\) is too little by comparing with higher ion stages. Figure 4: Theoretical tin spectra as a function of temperature and wavelength, convolution with a Gaussian profile of 0.06 nm full width at half maximum. (**a**) The variation of absolute emission as a function of \(T_{e}\). (**b**) Normalized to the peak at each temperature to compare the variation in profile. Figure 7 shows the 13.5 nm intensity in the 2% band (red, circle) and spectral purity (blue, star) as functions of laser-current delay. Here the spectral purity is defined as the ratio of 13.5 nm intensity in the 2% band to the range of 12.0 to 16.0 nm.