Broadband optical cavity methods

The combination of broadband light sources together with optical cavities has become a valuable atmospheric approach, uniting the selectivity of broad spectra with the sensitivity produced by optical cavities. Concentrations of key atmospheric gases as well as the optical properties of particles are now routinely measured with instruments based on this approach. This chapter gives an introduction to optical cavities and an overview of ringdown, cavity-enhanced, and phase shift measurements using optical cavities with broadband light sources and detectors. Instrument design, calibration approaches, and performance characterization are described. Example applications are presented in a range of measurement environments for NO₂, NO₃, and N₂O₅, HONO, glyoxal and methylglyoxal, halogens and their oxides, and several other species of atmospheric importance.