双色laser场控制下纳米针尖的高阶阈上光电发射
High-order above-threshold photoemission from nanotips controlled with two-color laser fields
摘要：
研究了双色激光场中尖锐金属纳米尖的相控高阶阈上光电发射过程。实验光电子光谱产生的双色激发与适度强烈的近红外基本场（1560 nm）和其弱的二次谐波显示出较强的相对相位和明确的指示高原状结构，这是由于弹性背散射的敏感性。为了探索相关的控制机制，特性的功能，并从近场不均匀性的特殊签名，我们进行了系统的量子模拟采用一维nanotip模型。除了丰富的相位相关的结构，在模拟的阈上电离（ATI）的光电子谱，我们发现有质动力位移以及近场的衰减长度的函数的再散射截止的实质性修改。为了探索所观察到的特征的量子或经典性质，并区分来自电子传播和电离率的双色效应，我们将量子结果与经典轨迹模拟进行比较。我们发现，直接电子的签名，以及在平台区的调制主要源于电离概率的控制，而在截止区的调制只能解释的双色场对电子轨迹的影响。尽管复杂的相位相关的功能，使双色强场光电发射从纳米尖端有趣的子周期强场控制，我们的研究结果支持，在截止区域的反射功能提供了一个强大的和可靠的方法来校准相对的双色相位。
英文摘要：
We investigate the process of phase-controlled high-order above-threshold photoemission from sharp metallic nanotips under bichromatic laser fields. Experimental photoelectron spectra resulting from two-color excitation with a moderately intense near-infrared fundamental field (1560 nm) and its weak second harmonic show a strong sensitivity on the relative phase and clear indications for a plateau-like structure that is attributed to elastic backscattering. To explore the relevant control mechanisms, characteristic features, and particular signatures from near-field inhomogeneity, we performed systematic quantum simulations employing a one-dimensional nanotip model. Besides rich phase-dependent structures in the simulated above-threshold ionization (ATI) photoelectron spectra we find ponderomotive shifts as well as substantial modifications of the rescattering cutoff as function of the decay length of the near-field. To explore the quantum or classical nature of the observed features and to discriminate the two-color effects stemming from electron propagation and from the ionization rate we compare the quantum results to classical trajectory simulations. We show that signatures from direct electrons as well as the modulations in the plateau region mainly stem from control of the ionization probability, while the modulation in the cutoff region can only be explained by the impact of the two-color field on the electron trajectory. Despite the complexity of the phase-dependent features that render two-color strong-field photoemission from nanotips intriguing for sub-cycle strong-field control, our findings support that the recollision features in the cutoff region provide a robust and reliable method to calibrate the relative two-color phase.
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