  We describe the emission, detection and structure of multiphoton states of
light. We include the effect of frequency filtering, which describes, at a
fundamental level, physical detection of a quantum emitter. The case of the
spontaneous emission of Fock states is treated fully and analytically. We
stress this picture by contrasting it to the numerical simulation of two-photon
bundles emitted from a two-level system in a cavity. We show that dynamical
factors exist that allow for a more robust multiphoton emission than
spontaneous emission. We also describe how this relates to thermal light.
