Why is Refractive Index Always so Small?
August 6th, 2019 DARRICK CHANG Theoretical Quantum-Nano Photonics
ICFO-The Institute of Photonic Sciences

A peculiar observation is that all the optical materials we know of have an index of refraction of order unity. Where does this effect come from? Is it due to complicated material chemistry? Or that we usually work with materials at wavelengths far away from their natural resonances? Here, we argue that the fact that thousands of materials can all have the same property must arise from some elegant and universal reason. In particular, we show that a dilute atomic gas, with a density billions of times smaller than that at which chemistry can occur, already exhibits a maximum refractive index of n~2, even close to the atomic resonance. We provide a simple argument showing that the saturation of index arises from purely electrodynamic effects, associated with multiple scattering of light, based on a novel renormalization group theory. This result presents a fascinating new perspective on the optical properties of materials, and stimulates the provocative question of whether these rules could be ever be broken, to realize an ultra-high index material.

Tuesday, August 6, 2019, 12:00. ICFO’s Blue Lecture Room