$10\text{−}\mathrm{Hz}$ grazing–incidence pumped Ni-like Mo x-ray laser

The operation of a Ni-like Mo x-ray laser at $18.9\mathrm{nm}$ with a repetition rate of $10\mathrm{Hz}$ has been demonstrated. The laser has been pumped applying the grazing incidence pump arrangement, where a short (picoseconds) pulse irradiates a Mo plasma column generated by a long (a few hundred picoseconds) pulse. The delayed short pulse is incident at a grazing angle on the plasma to heat it efficiently. We used a total energy of less than $450\mathrm{mJ}$ ($150\mathrm{mJ}$ in the long and $250–300\mathrm{mJ}$ in the short pulse) in a line focus of $7\mathrm{mm}$ by $50\mu \mathrm{m}$.

Figure 1

Sketch explaining the GRIP principle and double irradiation of the active area by the pump beam.

Figure 2

(Color online) Grazing incidence pumping (GRIP) scheme.

Figure 3

Dependence of the x-ray laser output signal on the delay between both pump pulses. Each measurement point is a result of averaging over 10 shots. Parameters as in Fig. 4.

Figure 4

Sequence of XRL pulses registered with a repetition rate of about $1\mathrm{Hz}$.

Figure 5

Delay temporal window for lasing achieved with more energetic pumping. The best results for each delay setting are shown.

Figure 6

Lineout of the image of lasing traced along the recorded line to determine the XRL beam divergence. The dips in the shape are caused by the supporting structure of the Al filter foil. For the pump pulse parameters, see Fig. 7a.

Figure 7

Soft x-ray spectrum with dominating Ni-like Mo lasing line at $18.9\mathrm{nm}$. The step in the spectrum at around $17.2\mathrm{nm}$ is caused by the absorption $L$ edge of Al used as a filter.

Figure 8

Dependence of the plasma density and average ionization stage on the distance from the target surface at the time of optimum delay. The simulation was performed with the prepulse parameters of the reported experiments at Max-Born-Institute (MBI, $1\times {10}^{11}\mathrm{W}∕{\mathrm{cm}}^2$, $400\mathrm{ps}$), Colorado State University [7] (CSU, $2.4\times {10}^{12}\mathrm{W}∕{\mathrm{cm}}^2$, $120\mathrm{ps}$), and Lawrence Livermore National Lab [2] (LLNL, $5\times {10}^{11}\mathrm{W}∕{\mathrm{cm}}^2$, $200\mathrm{ps}$).