A femtosecond (fs) broad-band absorption apparatus was used to measure the early photoisomeriza-tion process of bacteriorhodopsin’s (BR) photocycle to reveal the character of the important interme-diate of J625 and to obtain a deeper understanding of the role of photoisomerization in BR photocycle. Two time constants of 0.5 ps (95%) and 2.0 ps (5%) were brought out by global fitting on thirty curves in the near-infrared region. We suggest that the first time constant results from the decay of I460 interme-diate,and the longer component might be associated with BR isomer. The global analysis over 450,540,630,710 and 870 nm traces identified two time constants,～0.5 and～3 ps. The slower component can be extracted from the processes of both J625→BR568 (540 nm) and J625→K590 (630 nm),suggesting J-in-termediate takes a partial cis configuration. The obvious negative feature in early delay time of 700―780 nm regions was attributed to the radiative transition (stimulated emission) from the Franck-Condon active configuration along the isomerization potential surface of all-trans-retinal.
