A flash photolysis system, in which a very low-energy pulse of actinic light is highly correlated with the analysing light beam, is described. The performances of the system are exemplified by measuring, with a 3 ns time resolution, the singlet-singlet transient absorption signal of rhodamine 6G obtained with a 5 mu J excitation dye laser pulse and a non-pulsed 75 W xenon analysing light source.