To apply a laser ion source that generates a high-intensity pulsed beam to high-dose applications, such as ion implantation, a high repetition rate operation with a short pulse interval is required. However, when the pulse interval is shortened, there is a concern that a plasma, which is different from a single pulse plasma generation, may be formed due to the interaction between the preceding and following pulses. We investigated the time interval in which plasma pulses are generated without pulse-to-pulse interaction using a laser ion source with two lasers. In the experiment, a graphite target was irradiated by two laser beams (1064-nm wavelengths) with the same pulse widths (5.4 ns) and energies (15 mJ, 30 mJ, and 45 mJ) at different time intervals ranging from 1000 μs to 0 µs, and the time integrated value corresponding to the total charge amount was calculated from the measured time-of-flight signal of the generated carbon ion current. It was observed that the total charge did not change when the time interval was as low as approximately 100 µs, and the total charge rapidly decreased when the time interval was below approximately 100 µs. Thus, it was determined that the interaction occurs within a time interval of approximately 100 µs.

中文翻译：

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高重复率激光离子源等离子体产生时间间隔的研究

要将产生高强度脉冲束的激光离子源应用于高剂量应用，例如离子注入，需要以短脉冲间隔进行高重复率操作。然而，当脉冲间隔缩短时，由于前后脉冲之间的相互作用，可能会形成不同于单脉冲等离子体生成的等离子体。我们研究了使用带有两个激光器的激光离子源在没有脉冲到脉冲相互作用的情况下生成等离子体脉冲的时间间隔。在实验中，石墨靶被两束具有相同脉冲宽度（5.4 ns）和能量（15 mJ、30 mJ 和 45 mJ）的激光束（1064 nm 波长）照射，时间间隔从 1000 μs 到0 微秒，并且根据所产生的碳离子电流的飞行时间信号计算与总电荷量相对应的时间积分值。观察到，当时间间隔低至约 100 微秒时，总电荷没有变化，而当时间间隔低于约 100 微秒时，总电荷迅速减少。因此，确定交互发生在大约 100 µs 的时间间隔内。