Knowledge Bank

We report data from a new method, originally described by P. $Andresen1$ et al., that produces instantaneous 2-D images of state-specific molecular concentrations, and is ideal for observation of gaseous, turbulent reacting systems. This excimer-laser based approach yields state-specific 2-D distribution for each of a number of constituents and it should also yield temperature fields. The method applies within a wide temperature and pressure range because it is based upon a novel variant of laser induced fluorescence (LIF) which eliminates the collisional quenching that limits the quantitative use of normal LIF to pressures torr. This limitation is overcome by exciting molecules that are in a selected ground quantum state to predissociating states which are so short-lived (1-10ps) that there is no time for quenching collisions. The imaging technique uses a ribbon of narrow-band laser-light that passes through a medium. The laser's wavelength is tuned, in the range 193-193.8nm, to a desired transition. Fluorescence light is recorded by an intensified CCD camera that is pointed at $90\circ$ to the path of the light-ribbon. Our narrow-band laser is bright enough that a single pulse yields a 2-D image. The laser is also a flashbulb'' that determines the time scale. Our laser pulse lasts =15ns which is essentially stop action'' for turbulent phenomena. If we assume a molecular velocity of one km/s, a molecule would move only =15ns during the pulse. As an example, we show 2-D images of vibrationally excited $O2$ in several types of open flames