DIFFUSIONAL CHEMICAL-KINETICS OF REACTIVE SPECIES GENERATED IN LASER FIELDS

Under the irradiation of a general laser field, a specific spatial distribution of reactive radicals can be generated through the photodissociation of their precursor molecules. These radicals may undergo the processes of diffusion, first-order reaction, and recombination in a sample cell. The corresponding reaction-diffusion equation under general initial condition was solved numerically by a fast-Fourier-transform method. For a different approach one may assume that the spatial distribution of the reactive species remained self-similar and solve the equation analytically by Jaffe's approximation method. Compared with the numerical calculation, the analytical approximation is rather accurate under a wide range of experimental conditions but might be off by more than 50% if the recombination rate is much larger than the diffusion rate and/or the first-order reaction rate. The effect of higher order laser spatial modes on the measurements of the reaction rates is also discussed.