近日，瑞士苏黎世联邦理工学院Hans Jakob Wörner团队研究了非微扰复合驱动液体的多平台高次谐波产生。相关论文于2025年11月19日发表在《自然—光子学》杂志上。
最近在液相中观察到了非微扰高次谐波生成，其内在机制被证明不同于气体和固体中的谐波生成。目前对液相高次谐波生成的理解主要基于电子再碰撞机制，其中电子轨迹受电子散射限制。该机制成功复现了截止能量的特性及其对驱动激光参数的不依赖性。然而，当增强驱动激光强度时，并未观察到截止能量的扩展，这与大多数非线性介质的普遍预期相悖。
研究组在多种液体（水、重水、丙醇和乙醇）的高次谐波生成中观测到第二平台区的出现，并探究其成因。通过综合实验数据、计算结果与理论分析，研究组发现其源于在相邻分子位点（而非电离位点）复合的电子，并通过第二平台区产额对驱动场椭圆率的特征依赖性验证了这一特性。研究表明，第二平台区主要由在第一或第二溶剂化层复合的电子主导，这一过程依赖于空穴离域效应。理论结果预测更高平台区将会出现，表明这是一种普适规律。该工作确立了液体高度非线性光学响应中一种尚未被探索的物理现象。
附：英文原文
Title: Multi-plateau high-harmonic generation in liquids driven by off-site recombination
Author: Mondal, Angana, Neufeld, Ofer, Balinas, Tadas, Waser, Benedikt, Mller, Serge, Rossi, Mariana, Yin, Zhong, Rubio, Angel, Tancogne-Dejean, Nicolas, Wrner, Hans Jakob
Issue&Volume: 2025-11-19
Abstract: Non-perturbative high-harmonic generation has recently been observed in the liquid phase, and the underlying mechanism was shown to be different from that in gases and solids. Liquid-phase high-harmonic generation is currently understood in terms of a recollision mechanism with electron trajectories limited by electron scattering. The cut-off energy and its independence of the driving laser parameters are reproduced by this mechanism. However, when the driving laser intensity is increased, no extension of the cut-off energy is observed, which contrasts with the general expectations from most nonlinear media. Here we observe the appearance of a second plateau in high-harmonic generation from multiple liquids (water, heavy water, propanol and ethanol) and explore its origin. From the combined analysis of experimental, computational and theoretical results, we find that electrons recombining at neighbouring molecular sites instead of the ionization site are responsible and verify this feature through the characteristic dependence of the second-plateau yield on the ellipticity of the driving field. We find that the second plateau is dominated by electrons recombining at the first or second solvation shell, relying on hole delocalization. Theoretical results predict the appearance of yet higher plateaus, indicating a general trend. Our work establishes a previously unexplored physical phenomenon in the highly nonlinear optical response of liquid.
DOI: 10.1038/s41566-025-01805-y
Source: https://www.nature.com/articles/s41566-025-01805-y