A laser-induced fluorescence (LIF) model has been employed to characterize the shock tube/pulsed laser-induced fluorescence imaging method. The LIF model was first validated using experimental data for the reactions of H-abstraction by OH on benzene and toluene. The model was then employed to establish optical regime diagrams. Three regimes were distinguished: (i) the optically-thin regime, in which the rate constant obtained is not much affected by laser light absorption; (ii) the optically-thick regime, in which the laser absorption induces a significant error on the rate constant; and (iii) the so-called "non-physical" regime, in which the rate constant is negative.