Ultrashort pulsed laser sources generating pulse trains (bursts) with intra-burst repetition rates in the MHz and the GHz regime enable an efficient production of microstructures with a high surface quality. However, x-ray radiation can be generated during the laser micromachining using large intensities of the laser radiation and its interaction with the ablation cloud or high-density plasma. Therefore, the authors report on the interaction of bursts with a wavelength of 1030 nm and pulse durations of 0.24 and 10 ps with intra-burst repetition rates of 65 MHz (MHz-burst mode) and 2.5 GHz (GHz-burst mode) as well as a combination of both burst modes, called BiBurst mode, with stainless steel, and the x-rays are generated. The x-ray dose rates determined in the respective burst modes are compared and discussed with those of conventional ultrafast laser radiation (single-pulse mode). Furthermore, a theoretical model is used to calculate the expected x-ray dose rates. In the investigated parameter range, the highest dose rates of more than ${10}^5\mu$Sv/h are determined at a specific burst setting. Compared to the single-pulse mode, significantly higher dose rates are determined using the burst mode with the same total intensity. Based on the results of this study, it can be stated that the interaction of ultrafast laser radiation in the burst mode with a generated ablation cloud or high-density plasma plays a major role in x-ray generation and the resulting x-ray dose rates.

中文翻译：

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使用 MHz 至 GHz 脉冲串通过激光烧蚀生成 X 射线

超短脉冲激光源产生脉冲串（脉冲串），脉冲串内重复频率在 MHz 和 GHz 范围内，能够有效生产具有高表面质量的微结构。然而，在使用大强度激光辐射及其与烧蚀云或高密度等离子体的相互作用的激光微加工过程中，可以产生 X 射线辐射。因此，作者报告了波长为 1030 nm、脉冲持续时间为 0.24 和 10 ps 的脉冲串与 65 MHz（MHz 脉冲串模式）和 2.5 GHz（GHz 脉冲串模式）内脉冲串重复率的相互作用作为两种突发模式的组合，称为 BiBurst 模式，使用不锈钢，并产生 X 射线。将在各个突发模式中确定的 X 射线剂量率与传统超快激光辐射（单脉冲模式）的剂量率进行比较和讨论。此外，理论模型用于计算预期的 X 射线剂量率。在研究的参数范围内，最高剂量率超过${10}^5\mu$Sv/h 是在特定的突发设置下确定的。与单脉冲模式相比，使用具有相同总强度的突发模式可确定显着更高的剂量率。根据这项研究的结果，可以说突发模式中的超快激光辐射与产生的烧蚀云或高密度等离子体的相互作用在 X 射线产生和由此产生的 X 射线剂量率中起着主要作用.