Intense, ultrashort pulses of 800 nm laser light (12 fs, $\sim$4 opticalcycles) of peak intensity 5$\times$10$^{14}$ W cm$^{-2}$ have been used toirradiate gas-phase Xe$_n$ clusters ($n$=500-25,000) so as to induce multipleionization and subsequent Coulomb explosion. Energy distributions of explodingions are measured in the few-cycle domain that does not allow sufficient timefor the cluster to undergo Coulomb-driven expansion. This results in overalldynamics that appear to be significantly different to those in the many-cycleregime. One manifestation is that the maximum ion energies are measured to bemuch lower than those obtained when longer pulses of the same intensity areused. Ion yields are cluster-size independent but polarization dependent inthat they are significantly larger when the polarization is perpendicular tothe detection axis than along it. This unexpected behavior is qualitativelyrationalized in terms of a spatially anisotropic shielding effect induced bythe electronic charge cloud within the cluster.
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机译：峰值强度为5 $×10 $ ^ {14} $ W cm $ ^ {-2} $的峰值强度为800 nm的强超短脉冲（12 fs，$ \ sim $ 4光学周期）已用于辐照气相Xe $ _n $团簇（$ n $ = 500-25,000），以诱导多重化和随后的库仑爆炸。爆炸的能量分布是在几个周期的域中测量的，该域没有足够的时间让群集经历库仑驱动的扩展。这导致整体动力学似乎与多周期制中的显着不同。一种体现是，最大离子能量的测量结果远低于使用相同强度的较长脉冲时获得的离子能量。离子产量与簇大小无关，但与极化有关，因为当极化垂直于检测轴时，其离子产生量要大得多。根据簇中的电子电荷云引起的空间各向异性屏蔽效应，对这种意外行为进行了定性的定量化。
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