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Planar laser-induced fluorescence (PLIF) is an optical diagnostic technique widely used for flow visualization and quantitative measurements. PLIF has been shown to be used for velocity, concentration, temperature and pressure measurements. In PLIF, the flow is illuminated by a laser light sheet whose wavelength is tuned to excite a particular transition. A fraction of the ground state molecules of the flow absorbs the incident light and is excited to a higher electronic energy state. The excited species will after some time, usually in the order of few nanoseconds to microseconds, de-excite and emit light at a wavelength larger than the excitation wavelength. This light, fluorescence is captured on a digital camera.

A typical PLIF setup consists of a source of light (usually a laser), an arrangement of lenses to form a sheet, fluorescent medium, collection optics and a detector. The light from the laser (usually a beam) is passed through a set of lenses and/or mirrors to form a sheet, which is then used to illuminate the medium. This medium is either made up of fluorescent material or can be seeded with a fluorescent substance. The signal is usually captured by a CCD or CMOS camera and can be related to the various properties of the medium.

PLIF can provide accurate information which is both temporally resolved (usually to nanoseconds) and spatially resolved (routinely under 1 mm). In contrast, other techniques, e.g., emission and absorption spectroscopy and schlieren/shadowgraph techniques are averaged over a line of sight, and other spatially resolved techniques e.g., CARS, Raman scattering, and Rayleigh scattering typically have very low signal levels and have not been used to obtain 2-D spatial information.

Example of instant and statistical maps of concentration obtained with planar-LIF measurements

1. WIKI - PLIF
2. DANTEC Dynamics
3. Planar Laser Induced Fluorescence, Clemens Kaminski, Department of Chemical Engineering,University of Cambridge.
4. Introduction to Planar Laser-Induced Fluorescence (PLIF) by Dr. Ronald K. Hanson; Dr. Jay Jeffries; Dr. David Davidson.