The dye is excited by the light emitted from the laser, and re-emits light at a different wavelength. Light emitted from the fluorescent dye is proportional to the incoming laser light and the local concentration of the dye. If the dye is soluble in the liquid, then the concentration of the tagged dye may be determined locally in the fluid. Although this sounds quite simple, anyone who has performed PLIF experiments or looked at the details of a PLIF signal will know that there are many parameters and practicalities to consider in order to guarantee successful results. Dantec Dynamics has designed a number of tools, including optics, opto-electronics and software, which will enable experiments to be carried out with suitable accuracy.
Software is always a key element.
The first task in performing the measurement is to calibrate the system in situ. This can be appreciated by observing the details in the figure below. Both the average concentration and standard deviation have been calculated. Instantaneous concentration, average con- centration and standard deviation measured at a jet in a cross flow. The jet exit is 4 mm.