Kashiwagi H, Yamada K
Department of Advanced Radiation Technology, Takasaki Advanced Radiation Research Institute, Quantum Beam Science Research Directorate, National Institutes for Quantum and Radiological Science and Technology, 1233 Watanuki-machi, Takasaki, Gunma, Japan.
Rev Sci Instrum. 2020 Mar 1;91(3):033305. doi: 10.1063/1.5130999.
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.
为了将产生高强度脉冲束的激光离子源应用于诸如离子注入等高剂量应用中，需要进行具有短脉冲间隔的高重复率操作。然而，当脉冲间隔缩短时，存在这样的担忧：由于前后脉冲之间的相互作用，可能会形成与单脉冲等离子体产生不同的等离子体。我们使用具有两台激光器的激光离子源研究了在无脉冲间相互作用的情况下产生等离子体脉冲的时间间隔。在实验中，用两台具有相同脉冲宽度（5.4纳秒）和能量（15毫焦、30毫焦和45毫焦）的激光束（1064纳米波长）在1000微秒至0微秒的不同时间间隔下照射石墨靶，并根据所测量的产生的碳离子电流的飞行时间信号计算出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微秒时总电荷量没有变化，而当时间间隔低于约100微秒时总电荷量迅速下降。因此，确定相互作用发生在约100微秒的时间间隔内。
