Profiling a pulsed molecular beam with cavity-enhanced absorption spectroscopy

The molecular beam plays an important role in chemical dynamics experiments. The density in the beam is one of the critical factors influencing the reaction rate in these studies. Here we present a method based on laser-locked cavity-enhanced absorption spectroscopy to measure the molecular density in the beam. The P(1) transition in the second overtone band of CO was measured in the molecular beam, demonstrating a determination of the number density of molecules in a specific quantum state from the absorption spectrum. This non-destructive spectroscopic method allows the measurement of state-resolved properties of a molecular beam, which could be applied to various studies such as molecular collision dynamics.