Saturated planar laser-induced fluorescence using sinusoidal intensity modulation

Sammanfattning: Saturated laser-induced fluorescence (saturated LIF) has been the topic of some research, however mainly regarding laser diagnostic methods conducted on flames. A few papers have discussed saturated LIF with the purpose of producing saturation curves of different fluorescent elements. The utilised methods in these cases have involved manually increasing the laser intensity and detecting the fluorescence intensity after each increment. The method proposed here involves conducting saturated planar laser-induced fluorescence, or saturated PLIF, using structured light in order to increase the efficiency of producing a saturation curve. Due to the intensity distribution of the structured light, it is possible to obtain a range of intensities from a single measurement. The response of the detected fluorescence signal is then compared to the signal of the laser which irradiates the sample in order to produce a saturation curve. To the best of the author’s knowledge, no previous studies have used the method described above. Using this method, saturation curves for Rhodamine B, Rhodamine 560, Fluorescein, and Coumarin 153 were obtained using only one image of the saturated sample and one reference image in each case. The saturation curves were all distinguishable from each other, thus strongly suggesting that the method in this project can be used to differentiate between fluorophores. Clear dependencies on lifetime and absorption cross section were detected when analysing the saturation curves. This observation indicates that the method used in the project has the potential of being used in several cases where laser diagnostic methods for analysing fluorophores are wanted.