6: Emission and Absorption of Photons

6.1: Transitions Between Stationary States
We casually claim that quantum states "drop" to a lower energy state when they emit a photon. But why would a quantum state change at all if it is in a "stationary" state?
6.2: Selection Rules and Transition Times
While perturbations act to trigger transitions between states, not all perturbations are created equal.
6.3: Lasers
We take a brief look at the inner workings of what is now a ubiquitous technology.