A buffer gas beam source for short, intense and slow molecular pulses

Experiments with cold molecules usually begin with a molecular source. We describe the construction and characteristics of a cryogenic buffer gas source of CaF molecules. The source emits pulses with a typical duration of 240 $\mu$s, a mean speed of about 150 m/s, and a flux of $5\times {10}^{10}$ molecules per steradian per pulse in a single rotational state.