Enhanced acceleration of protons to high energy by relatively modest high power ultra-short laser pulses, interacting with snow micro-structured targets was recently proposed. A notably increased proton energy was attributed to a combination of several mechanisms such as localized enhancement of the laser field intensity near the tip of $1~\unicode[STIX]{x03BC}\text{m}$ size whisker and increase in the hot electron concentration near the tip. Moreover, the use of mass-limited target prevents undesirable spread of absorbed laser energy out of the interaction zone. With increasing laser intensity a Coulomb explosion of the positively charged whisker will occur. All these mechanisms are functions of the local density profile and strongly depend on the laser pre-pulse structure. To clarify the effect of the pre-pulse on the state of the snow micro-structured target at the time of interaction with the main pulse, we measured the optical damage threshold (ODT) of the snow targets. ODT of $0.4~\text{J}/\text{cm}^{2}$ was measured by irradiating snow micro-structured targets with 50 fs duration pulses of Ti:Sapphire laser.

中文翻译：

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飞秒激光诱导雪中微结构目标的损伤阈值

最近提出了通过与雪微结构目标相互作用的相对适中的高功率超短激光脉冲来增强质子向高能的加速。质子能量的显着增加归因于多种机制的组合，例如在尖端附近的激光场强度的局部增强。$1~\unicode[STIX]{x03BC}\text{m}$尺寸晶须和增加尖端附近的热电子浓度。此外，使用质量有限的目标可以防止吸收的激光能量不希望地扩散到相互作用区之外。随着激光强度的增加，带正电的晶须会发生库仑爆炸。所有这些机制都是局部密度分布的函数，并且强烈依赖于激光预脉冲结构。为了阐明预脉冲对雪微结构目标在与主脉冲相互作用时状态的影响，我们测量了雪目标的光学损伤阈值（ODT）。ODT 的$0.4~\text{J}/\text{cm}^{2}$通过用 50 fs 持续时间的 Ti:Sapphire 激光脉冲照射雪微结构目标来测量。