Planar laser-induced fluorescence (PLIF) is an optical diagnostic technique widely used for

flow visualization Flow visualization or flow visualisation in fluid dynamics is used to make the flow patterns visible, in order to get qualitative or quantitative information on them. Overview Flow visualization is the art of making flow patterns visible. ...

and quantitative measurements. PLIF has been shown to be used for velocity, concentration, temperature and pressure measurements.

Working

A PLIF setup consists of a source of light (usually a

laser A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation". The fir ...

), an arrangement of lenses to form a sheet,

fluorescent Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. It is a form of luminescence. In most cases, the emitted light has a longer wavelength, and therefore a lower photon energy, tha ...

medium, collection optics and a detector. The light from the source, illuminates the medium, which then fluoresces. This signal is captured by the detector and can be related to the various properties of the medium. The typical lasers used as light sources are pulsed, which provide a higher peak power than the continuous-wave lasers. Also the short pulse time is useful for good

temporal resolution Temporal resolution (TR) refers to the discrete resolution of a measurement with respect to time. Physics Often there is a trade-off between the temporal resolution of a measurement and its spatial resolution, due to Heisenberg's uncertainty pri ...

. Some of the widely used laser sources are Nd:YAG laser,

dye laser A dye laser is a laser that uses an organic dye as the lasing medium, usually as a liquid solution. Compared to gases and most solid state lasing media, a dye can usually be used for a much wider range of wavelengths, often spanning 50 to 100 na ...

excimer laser An excimer laser, sometimes more correctly called an exciplex laser, is a form of ultraviolet laser which is commonly used in the production of microelectronic devices, semiconductor based integrated circuits or "chips", eye surgery, and microm ...

s, and

ion laser An ion laser is a gas laser that uses an ionized gas as its lasing medium. Like other gas lasers, ion lasers feature a sealed cavity containing the laser medium and mirrors forming a Fabry–Pérot resonator. Unlike helium–neon lasers, the e ...

s. 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 Complementary metal–oxide–semiconductor (CMOS, pronounced "sea-moss", ) is a type of metal–oxide–semiconductor field-effect transistor (MOSFET) fabrication process that uses complementary and symmetrical pairs of p-type and n-type MOSFE ...

camera A camera is an Optics, optical instrument that can capture an image. Most cameras can capture 2D images, with some more advanced models being able to capture 3D images. At a basic level, most cameras consist of sealed boxes (the camera body), ...

(sometimes intensified cameras are also used). Timing electronics are often used to synchronize pulsed light sources with intensified cameras.

Basic principles

Comparison with other techniques

Advantages

- Unlike several other flow imaging techniques, PLIF may be combined with particle image velocimetry (PIV). This allows for the simultaneous measurement of a fluid velocity field and species concentration.

Limitations

# flowfield must contain molecular species with an optical resonance wavelength that can be accessed by laser # temperature measurements typically require two laser sources # velocity measurements typically practical only for high Mach number flows (near sonic or supersonic) # signal-to-noise ratio often limited by detector shot-noise # fluorescence interferences from other species, especially from hydrocarbons in high pressure reacting flows # attenuation of laser sheet across flow field or reabsorption of fluorescence before it reaches detector can lead to systematic errors

Applications

References

* {{cite book , editor = Taylor, A. M. K. P. , title = Instrumentation for Flows with Combustion , publisher =

Academic Press Academic Press (AP) is an academic book publisher founded in 1941. It was acquired by Harcourt, Brace & World in 1969. Reed Elsevier bought Harcourt in 2000, and Academic Press is now an imprint of Elsevier. Academic Press publishes reference ...

, year = 1993 , isbn = 978-0-12-683920-3 , chapter = Planar Fluorescence Imaging in Gases , last = Seitzman , first = J. M. , author2=Hanson, R. K. , pages = 405–466 Measurement Fluid dynamics