The lecture gives an overview on the concepts of optical spectroscopy under weak excitation and presents corresponding experi mental examples. Classical dispersion theory of optical excitation: resonance and relaxation processes, metals and insulators. Quantum mechanical descriptions:
Perturbation theory from atoms to solids: Fermi’s Golden Rule. Collective excitation: harmonic oscillators and the concept of excitons. Local field corrections, the polarization field and dipolar interaction. The concept of polaritons, coupled states of light and matter. Non-local response and spatial dispersion, optical anisotropy and directional dispersion.