In cyanine dye, a photo-isomerization path involving a multiphoton process was found in addition to a conventional reaction path with a one-photon process by two-pulse correlation of transient absorption and bleaching. That photo-isomerization was completed within 3 ns and its efficiency was dependent on the interval time between two pump pulses indicate that the new path involves a multiphoton process: S-0 -> S-n -> S-m, where S-n is similar to 3.1 eV and Sm is similar to 4.7 eV higher than S-0 and the lifetime of intermediate state in S-n is approximately 0.2 ps. Changing the pump power controlled the branching ratio between the two paths. (c) 2010 Elsevier B. V. All rights reserved.