Abstract
Nanocomposites, i.e., materials comprising nano-sized entities embedded in a host matrix, can have tailored optical properties with applications in diverse fields such as photovoltaics, bio-sensing, and nonlinear optics. Effective medium approaches such as Maxwell-Garnett and Bruggemann theories, which are conventionally used for modeling the optical properties of nanocomposites, have limitations in terms of the shapes, volume fill fractions, sizes, and types of the nanoentities embedded in the host medium. We demonstrate that grating theory, in particular the Fourier Eigenmode Method, offers a viable alternative. The proposed technique based on grating theory presents nanocomposites as periodic structures composed of unit-cells containing a large and random collection of nanoentities. This approach allows us to include the effects of the finite wavelength of light and calculate the nanocomposite characteristics regardless of the morphology and volume fill fraction of the nano-inclusions. We demonstrate the performance of our approach by calculating the birefringence of porous silicon, linear absorption spectra of silver nanospheres arranged on a glass substrate, and nonlinear absorption spectra for a layer of silver nanorods embedded in a host polymer material having Kerr-type nonlinearity. The developed approach can also be applied to quasi-periodic structures with deterministic randomness or metasurfaces containing a large collection of elements with random arrangements inside their unit cells.
Highlights
Nanocomposites have recently emerged as viable alternatives to conventional bulk optical materials because they offer on-demand customization of linear and nonlinear optical properties by tailoring the size, shape, and types of nano-inclusions [1]
The theory of nanocomposite optical response is still limited to the effective medium models (e.g., Maxwell Garnett (MG) model [28]), which are based on quasi-static approximation and can be employed only at low volume fractions of the inclusions [29]
In the vicinity of the percolation threshold, when the large clusters of nanoparticles and their long-range coupling essentially contribute to the optical response, MG theory cannot provide a consistent picture of the light-matter interaction [30]
Summary
Nanocomposites have recently emerged as viable alternatives to conventional bulk optical materials because they offer on-demand customization of linear and nonlinear optical properties by tailoring the size, shape, and types of nano-inclusions [1]. Nowadays, calculating the linear and nonlinear refractive index and absorption coefficient of nanocomposites often relies on numerical simulations [32,33], including machine learning-assisted approaches, which require an enormous amount of experimental training datasets [34,35,36] and are hardly feasible. This makes it essential to develop theoretical models and/or numerical techniques capable of predicting the optical properties of nanocomposites and of bridging the gap between optical design and material fabrication. We estimate the effective Kerr nonlinearity of a nanocomposite consisting of silver nanorods in a nonlinear dielectric host medium by studying the change in absorption spectra with an increase of the incoming light field intensity
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