I need information about the effects of optical coupling, and can this effect compete with refraction index?
Dear Eduar, you can use an index matching (liquid) material for coupling between them, we use this method for fiber optic coupling. The index of this liquid must be between the index of your materials.
Can you be more specific towards what in particular you are concerned? Optical coupling is generally the result of electromagnetic field interactions. In the context of nanomaterials, I can think of two immediate circumstances that are possibly germane to your question. The first is in thin films. Generally, a very thin film of absorbing material (such as gold) can intercept the electromagnetic field of light waves propogating along a boundary. In many cases, one refers to the evanescent wave along the boundary, which is essentially a leaky light field that propogates along a boundary of a material over which light is obliquely incident (for example transverally along the core-cladding interface of an optical fiber). The thin film will absorb this wave and energy is lost.
In terms of metallic nanoparticles, when brought into close proximity, their electromagentic fields will interact, and as a result, two neighboring nanoparticles will scatter and absorb light (together these effects are called extinction) differently than say just one nanoparticle, or 3, or 5 etc...
The index of refraction is ubuquitously affecting all of these processes. The index of refraction determines the light propogation properties in any material, so I don't know what you mean by "compete" with the refraction index. For certain, one can modify any nanomaterial system by altering the indicies of refraction of the composite materials, and with judicious choices, can enhance or deflate a particular optical response of the system. But AFAIK, there's not "competing" going on.
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