Picosecond lidar techniques in laboratory and field diagnostics

The availability of picosecond laser systems opens a new potential in the field of diagnostics. It is now possible to observe chemical events over time intervals as short as 10 to the minus 9th power sec (e.g., fluorescence, bond-selective chemistry,...) without overlap with the much shorter 10 to the minus 12th power sec triggering signal. In addition, two specific effects are of special interest to real industrial flame diagnostics. One is the elimination of background noise, since the picosecond time-gating of the detector will collect the whole signal of interest but only a tiny fraction of the time-spread noise background (e.g., soot, walls,...). The other is related to the very short length of these pulses (similar to mm): it is the possibility to use the lidar/radar principle to convert the time history of the measured back scattered signals into a millimeter-resolved space distribution along the beam. In this fashion, Raman and other techniques can yield a detailed map of concentrations and temperatures in three-dimensional space, even in sooty combustors background, with the need of only one single porthole.