School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138.
Proc Natl Acad Sci U S A. 2014 Feb 11;111(6):E639-44. doi: 10.1073/pnas.1323392111. Epub 2014 Jan 27.
Many experimental systems consist of large ensembles of uncoupled or weakly interacting elements operating as a single whole; this is particularly the case for applications in nano-optics and plasmonics, including colloidal solutions, plasmonic or dielectric nanoparticles on a substrate, antenna arrays, and others. In such experiments, measurements of the optical spectra of ensembles will differ from measurements of the independent elements as a result of small variations from element to element (also known as polydispersity) even if these elements are designed to be identical. In particular, sharp spectral features arising from narrow-band resonances will tend to appear broader and can even be washed out completely. Here, we explore this effect of inhomogeneous broadening as it occurs in colloidal nanopolymers comprising self-assembled nanorod chains in solution. Using a technique combining finite-difference time-domain simulations and Monte Carlo sampling, we predict the inhomogeneously broadened optical spectra of these colloidal nanopolymers and observe significant qualitative differences compared with the unbroadened spectra. The approach combining an electromagnetic simulation technique with Monte Carlo sampling is widely applicable for quantifying the effects of inhomogeneous broadening in a variety of physical systems, including those with many degrees of freedom that are otherwise computationally intractable.
许多实验系统由大量不耦合或弱相互作用的元素组成，作为一个整体运作；这在纳米光学和等离子体学的应用中尤其如此，包括胶体溶液、衬底上的等离子体或介电纳米粒子、天线阵列等。在这种实验中，由于元素之间的微小差异（也称为多分散性），即使这些元素被设计为相同，集合的光学光谱测量结果将不同于独立元素的测量结果。特别是，由于窄带共振引起的尖锐光谱特征往往会显得更宽，甚至可能完全消失。在这里，我们研究了这种不均匀展宽效应对包含自组装纳米棒链的胶体纳米聚合物的影响。我们使用结合有限差分时域模拟和蒙特卡罗抽样的技术，预测了这些胶体纳米聚合物的不均匀展宽的光学光谱，并观察到与未展宽光谱相比存在显著的定性差异。这种将电磁模拟技术与蒙特卡罗抽样相结合的方法广泛适用于量化各种物理系统中的不均匀展宽效应，包括那些具有许多自由度的系统，否则这些系统在计算上是难以处理的。
