2-DIMENSIONAL DIRECT QUENCHING MEASUREMENT OF OH IN A CROSS-SECTION OF A BUNSEN FLAME

In flame analysis, the laser-induced fluorescence (LIF) method is beco ming popular for detecting intermediate species and measuring temperat ure. However, when a typical tunable laser with a pulse duration of ar ound 10 ns is used, the pressure of the target to be measured is often too high to obtain a fluorescent signal having a linear relationship to molecular concentration, due to collisional quenching by which rela xation without fluorescence occurs. In a reactive field such as a flam e, especially when two-dimensional measurement is desired, the problem of quenching is more serious because the quenching time constant diff ers at each measuring point. Accordingly, an effective two-dimensional quenching measurement method is desirable. For this purpose, we attem pted to determine the quenching time constant distribution, using an i mage intensifier and a XeCl excimer-laser-pumped dye laser with a doub ling crystal, which is the typical and widely used tunable laser, at t he pressure at which the LIF signal is significantly affected by colli sional quenching. In this way, we succeeded in determining the quenchi ng time-constant distribution in the cross section of a premixed Bunse n flame at 1/2 atmospheric pressure. In addition, this experiment is t he first measurement of two-dimensional fluorescence decay time on the order of a few nanoseconds.