Department of Physics, Imperial College London, South Kensington Campus, London SW7 2AZ, UK.
Max-Born-Institut, Max-Born-Strasse 2A, 12489 Berlin, Germany.
Sci Rep. 2016 Dec 23;6:39664. doi: 10.1038/srep39664.
The interaction of intense laser pulses with nanoscale particles leads to the production of high-energy electrons, ions, neutral atoms, neutrons and photons. Up to now, investigations have focused on near-infrared to X-ray laser pulses consisting of many optical cycles. Here we study strong-field ionization of rare-gas clusters (10 to 10 atoms) using two-cycle 1.8 μm laser pulses to access a new interaction regime in the limit where the electron dynamics are dominated by the laser field and the cluster atoms do not have time to move significantly. The emission of fast electrons with kinetic energies exceeding 3 keV is observed using laser pulses with a wavelength of 1.8 μm and an intensity of 1 × 10 W/cm, whereas only electrons below 500 eV are observed at 800 nm using a similar intensity and pulse duration. Fast electrons are preferentially emitted along the laser polarization direction, showing that they are driven out from the cluster by the laser field. In addition to direct electron emission, an electron rescattering plateau is observed. Scaling to even longer wavelengths is expected to result in a highly directional current of energetic electrons on a few-femtosecond timescale.
强激光脉冲与纳米级粒子相互作用会产生高能电子、离子、中性原子、中子和光子。迄今为止，研究主要集中在近红外到 X 射线激光脉冲上，这些激光脉冲由多个光周期组成。在这里，我们使用两周期 1.8μm 激光脉冲研究稀有气体团簇（10 到 10 个原子）的强场电离，以进入一个新的相互作用区域，在这个区域中，电子动力学由激光场主导，而团簇原子没有时间发生显著移动。当使用波长为 1.8μm、强度为 1×10W/cm 的激光脉冲时，可以观察到动能超过 3keV 的快速电子发射，而在使用类似强度和脉冲持续时间的 800nm 激光时，只能观察到低于 500eV 的电子。快速电子优先沿激光偏振方向发射，表明它们是被激光场从团簇中驱出的。除了直接电子发射之外，还观察到电子再散射平台。预计向更长的波长扩展将导致在几飞秒时间尺度上产生高能电子的高度定向电流。
