The field of chiral nanoparticles is rapidly expanding, yet measuring the chirality of single nano-objects remains a challenging endeavor. Here, we report a technique to detect chiro-optical effects in single plasmonic nanoparticles by means of phase-sensitive polarization-resolved four-wave mixing interferometric microscopy. Beyond conventional circular dichroism, the method is sensitive to the particle polarizability, in amplitude and phase. First, we demonstrate its application on single chiral nanohelices fabricated by focused ion beam induced deposition. We examined the combination of detected fields, which measures the particle polarizability, and showed that this is a sensitive reporter of chirality, providing dissymmetry factors (g_α) impressively approaching unity. We then applied the method to a set of individual small gold nanoparticles near the dipole limit (60 nm nominal size), having correspondingly small chiral effects from the intrinsic lattice defects and nonperfectly spherical shape. We find that g_α is randomly distributed in the population, consistent with its nondeterministic origin, but again exhibits remarkably high values, an order of magnitude higher than those obtained using conventional light absorption. Considering the importance of chiral plasmonic nanoparticles in fields ranging from catalysis to metamaterials, this technique offers a powerful way to quantify chiro-optical effects at the single particle level with unprecedented sensitivity.

中文翻译：

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通过四波混合干涉测量法高灵敏度检测单个纳米颗粒中的手光效应


手性纳米粒子的领域正在迅速扩大，但测量单个纳米物体的手性仍然是一项具有挑战性的工作。在这里，我们报道了一种通过相位敏感偏振分辨四波混合干涉显微镜检测单个等离子体纳米颗粒中手环光学效应的技术。与传统的圆二色性相比，该方法对粒子的振幅和相位极化率很敏感。首先，我们展示了它在通过聚焦离子束诱导沉积制备的单个手性纳米螺旋上的应用。我们检查了测量粒子极化率的检测场的组合，并表明这是手性的敏感报告因子，提供了令人印象深刻地接近一的不对称因子 （g_α）。然后，我们将该方法应用于偶极子极限（60 nm 标称尺寸）附近的一组单个小金纳米颗粒，这些颗粒具有来自本征晶格缺陷和非完美球形的相应小手性效应。我们发现 g_α 在种群中随机分布，与其非确定性起源一致，但再次表现出非常高的值，比使用常规光吸收获得的值高一个数量级。考虑到手性等离子体纳米粒子在从催化到超材料等领域的重要性，该技术提供了一种强大的方法，以前所未有的灵敏度在单个粒子水平上量化手光效应。