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Laser-Induced Fluorescence

a green laser shining in an otherwise dark space
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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 [1]! Currently, the Hanson Research Group is developing a LIF-based diagnostic for sensing gasdynamic parameters in high-enthalpy test facilities.

Diagram of a laser-induced experiment
Schematic of laser-induced fluorescence experimental setup. Adapted from [1]

To learn more, check out some of our publications:

[1] 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