Planar Laser-Induced Fluorescence
In a typical Planar Laser-Induced Fluorescence (PLIF) experiment, a laser beam is expanded in one dimension while reduced in another, to yield a planar laser sheet (Fig. 1). This sheet is then directed into a gaseous or liquid flow, doped with a molecular tracer. The wavelength of the incident beam is tuned to excite a particular transition of the molecular tracer, such as acetone which is used in our laboratory.
Fig. 1: A cylindrical telescope (a) transforming a round beam (b) into a planar one (c).
When the process involves the emission of photons it is termed photoluminescence. In the case where the upper and lower energy states have the same spin, the excitation is short lived and results in fluorescence. If, on the other hand, intersystem crossing to a different spin occurs, the emission involves a dipole-forbidden transition, resulting in the much slower phosphorescence from the metastable state.
The emitted light is then collected onto a camera to acquire a 2D map of the gas concentrations in the illuminated plane. The use of a narrow laser sheet ensures a clean cross section of the flow, whereas using an elongated sheet gives the entire cross section in a single frame (Fig. 2).
Fig. 2: Mapping of the entire cross section of a triple gas-puff is obtained in a single frame when using a planar beam.
Modified on: 2010-05-23