纳米针尖的极强光波电子场发射
Extreme Lightwave Electron Field Emission from a Nanotip
摘要：
我们报告子周期太赫兹光场发射的电子从钨纳米尖在极端条件下对应的Keldysh参数$γ_K\approx10^{-4}$。局部峰值太赫兹场达到40~GV/m的照射纳米尖端的顶点，导致亚循环冷场电子发射和加速在准静态场。通过同时测量电子束团电荷和能量分布，我们进行了准静态Fowler-Nordheim隧穿理论的定量测试场条件下，完全抑制隧道势垒。观察到$\sim10^6$电子/脉冲的非常高的聚束电荷，在局部场中加速后达到3.5 keV的最大能量。能量分布和发射电流表现出良好的协议与福勒Nordheim理论，即使在这种极端的领域制度。在这些条件下，将该模型扩展到单次激发制度，预测峰值电子分布的光谱纯度为$10^{-4}$。观察到太赫兹场诱导的纳米尖端的整形和锐化，在大约$10^9$太赫兹照射下，尖端半径从120 nm减小到35 nm。这些结果表明，太赫兹驱动的纳米尖端在极端的领域限制是有前途的电子源的超快电子衍射和显微镜。
英文摘要：
We report on sub-cycle terahertz light-field emission of electrons from tungsten nanotips under extreme conditions corresponding to a Keldysh parameter $γ_K\approx10^{-4}$. Local peak THz fields up to 40~GV/m are achieved at the apex of an illuminated nanotip, causing sub-cycle cold-field electron emission and acceleration in the quasi-static field. By simultaneous measurement of the electron bunch charge and energy distribution, we perform a quantitative test of quasi-static Fowler-Nordheim tunnelling theory under field conditions that completely suppress the tunnel barrier. Very high bunch charges of $\sim10^6$ electrons/pulse are observed, reaching maximum energies of 3.5~keV after acceleration in the local field. The energy distribution and emission current show good agreement with Fowler-Nordheim theory even in this extreme field regime. Extending this model to the single-shot regime under these conditions predicts peak electron distributions with a spectral purity of $10^{-4}$. THz field-induced reshaping and sharpening of the nanotip is observed, reducing the tip radius from 120~nm to 35~nm over roughly $10^9$ THz shots. These results indicate THz-driven nanotips in the extreme field limit are promising electron sources for ultrafast electron diffraction and microscopy.
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