On high spatial resolution scalar measurement with LIF - Part 2: The noisecharacteristic

A spatial resolution of about 4 (mu m)(3) for scalar measurement in turbule nt mixing with Laser-Induced-Fluorescence is realized in this experiment. I t is shown that for the high spatial resolution the signal is weak because of the measuring volume is very fine. The corresponding main problem is tha t the signal to noise ratio is small, especially for the high frequency sig nal corresponding to small structures. It is shown that the dominating nois e is the shot noise in the signal from the photomultiplier tube. The measur ement results indicate that an increase of the signal level through the inc rease of dye concentration and/or laser power is limited, mainly due to the rmal blooming and photobleaching.