Intersubband polaritons in photonic crystal cavities

This thesis deals about the physics of light-matter coupling between the intersubband excitation in a semiconductor quantum well and the electromagnetic resonance supported by a metallo-dielectric photonic crystal cavity - i.e., an implementation of a plasmonic metasurface.
After an introductory chapter where the electronic and optical properties of quantum wells are reviewed, we give a theoretical model for light-matter interaction across the weak and strong coupling regimes, highlighting connections with the critical coupling concept and the coherent perfect absorption (CPA) phenomenon.
Next we provide two chapters with experimental data collected in the linear and in the non-linear regimes of optical excitation. Experimental evidence of polariton CPA, of polariton saturation (bleaching) and of polariton-enabled ultrafast tuning of a photonic bandstructure are the main results - fully supported by theoretical analysis.
In addition to the relevance as fundamental physics, the data and the concepts analyzed in this thesis pose the basis for the development of efficient mid-infrared and terahertz light sources.