AVOIDANCE OF THE PHOTOCHEMICAL PRODUCTION OF OXYGEN-ATOMS IN ONE-DIMENSIONAL, 2-PHOTON LASER-INDUCED FLUORESCENCE IMAGING

We demonstrate that one-dimensional, two-photon laser-induced fluoresc ence imaging of oxygen atoms in flames can be achieved with reasonable signal intensities and spatial resolution but without the interferenc e caused by the photolysis of O2, by the use of a beam telescope inste ad of a focusing lens. The increase in probed volume (and concomitantl y the number of excitable atoms) caused by the larger beam diameter in the telescope experiments offsets, to a certain extent, the lose in s ignal that is due to the reduced laser fluence. Further, the results s how that the ''correct'' dependence of the fluorescence intensity on l aser fluence (in this case quadratic) does not guarantee the absence o f photochemistry.