The book “Photons and Atoms: Introduction to Quantum Electrodynamics” by Claude Cohen-Tannoudji, Gilbert Grynberg, and Jacques Dupont-Roc is beautiful and excellent, and a must-read for those who are interested in the fundamentals of light-matter interaction. While the focus is on atoms, I found most of the contents apply for molecules and ions as well. The discussion with gauge transformation is particularly clear, both perspectives from the Lagrangian and from the Hamiltonian formalism are presented.
Since it contains all the essential knowledge in the beginning of the book, it is rather self-contained. But a basic knowledge of quantum mechanics (first and second quantization for non-relativistic particles) and quantum optics (photons) are quite useful.