The authors show the prepulse effect on the conversion efficiency of a visible laser into water-window (λ=2.3-4.4 nm) x ray from a liquid nitrogen jet. It is observed that a prepulse of only 2 mJ enhances the conversion efficiency by 10-15 times for the main pulse of 15-60 mJ at a delay of 3-6 ns. The photon flux is ～1.2 X 10~(12) photons/pulse sr at a delay of 4 ns for a main pulse of 60 mJ with a prepulse of 4-8 mJ. It is noticed that the conversion efficiency increases with the delay up to 3 ns and is then saturated.
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机译：作者展示了预脉冲对可见激光转换为液氮射流的水窗（λ= 2.3-4.4 nm）x射线的转换效率的影响。可以看到，对于主脉冲15-60 mJ，只有3 m ns的延迟，只有2 mJ的预脉冲可以将转换效率提高10-15倍。对于60 mJ的主脉冲和4-8 mJ的主脉冲，光子通量在〜4 ns的延迟下为〜1.2 X 10〜（12）个光子/脉冲sr。值得注意的是，转换效率随着延迟的增加而增加，延迟高达3 ns，然后达到饱和。
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