FLUIDS BY MEANS OF A TWO-DYE LASER INDUCED FLUORESCENCE RATIOMETRIC SCHEME: 2D THICKNESS AND TEMPERATURE MAPPING

摘要

This paper presents the principles behind the use of a two-dye Laser Induced Fluorescence (LJF) technique for two-dimensional film thickness and tempera mapping of fluids. The need for two fluorescent emissions arises as a consequence of the fluorescence dependence on excitation light intensity. A ratiometric scheme that normalizes the. fluorescent emission of one dye against the fluorescent emission of a second dye is used in order to eliminate undesirable effects due to illumination intensity fluctuations, in both space and time, and optical distortions. The same ratiometric scheme is applied for both film thickness and temperature measurements, but the required spectra characteristics of the dyes used and the optical conditions differ significantly between the two measurements. The concepts of emission reabsorption and optical thickness are discussed in light of the requirements for each particular measurement. Experimental validation of the technique in measuring the thickness and temperature of a film of lubricating oil is also presented.