On high spatial resolution scalar measurement with LIF Part 2: The noise characteristic

Abstract

A spatial resolution of about 4 (m)³ for scalar measurement in turbulent mixing with Laser-Induced-Fluorescence is realized in this experiment. It 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 that the signal to noise ratio is small, especially for the high frequency signal corresponding to small structures. It is shown that the dominating noise is the shot noise in the signal from the photomultiplier tube. The measurement results indicate that an increase of the signal level through the increase of dye concentration and/or laser power is limited, mainly due to thermal blooming and photobleaching.