Laser-induced fluorescence (LIF) is a diagnostic technique leveraging the spontaneous emission of light from an excited atom or molecule.
A target chemical species such as carbon dioxide (CO2), hydroxyl (OH), nitric oxide (NO), or potassium (K) is excited to a high-energy state with a laser. As the excited-state species returns to its original energy state, it emits a photon through the process known as fluorescence, and this fluorescence signal is monitored at an angle to the excitation beam.
Many traditional diagnostic techniques, such as absorption/emission spectroscopy and schlieren, are line-of-sight averaged. However, due to the omnidirectionality of fluorescence, LIF can provide measurements of temperature, pressure, species concentration, and velocity with spatial resolution of 1 mm3 or less along the excitation beam path ! Currently, the Hanson Research Group is developing a LIF-based diagnostic for sensing gasdynamic parameters in high-enthalpy test facilities.
To learn more, check out some of our publications:
 S. K. Wang, C. L. Strand, R. K. Hanson, “Spectrally-Resolved Absorption and Laser-Induced Fluorescence of High-Temperature Gases,” AIAA SciTech Forum (2019) DOI: 10.2514/6.2019-1612