We present experimental results on the measurement of the population-relaxation times of the excited states of some metalloporphyrins such as zinc meso-tetra-phenylporphyrin(ZnmTPP), zinc meso-tetra (p-methoxyphenyl) tetrabenzporphyrin(ZnmpTBP), tetratollylporphyrin (TTP), cobalt tetratollylporphyrin (CoTTP)and nickel tetratollylporphyrin (NiTTP) with time-resolved degenerate four-wavemixing with the incoherent emission of a nanosecond pumped-dye laser. The experiments are carried out in the counterpropagating geometry (k4 = k1 + k2 − k3), where k1and k2 are counterpropagating toone another and k3 is at angle θ(<90° with respect to k1). Excited-state and ground-state relaxation times are calculated based on the theoretical formalism developed by Hiromi Okamoto [J. Opt. Soc.Am. B, 10, 2353, 1993]. The signals are recorded by delaying the probe beam (k3) for different fixed delays of the backward pump beam (k2). We observe strong signal at a second peak owing to the coherence of beams k2 and k3 for samples exhibiting excited-state absorption and a narrow peak corresponding to the coherence of beams k1 and k3for samples that do not exhibit excited-state or reverse-saturable absorption. The nonlinear absorption is studied with the Z-scan technique. From the experimental data, we estimate the relaxation times of excited states.
© 1997 Optical Society of America
D. Narayana Rao, S. Venugopal Rao, F. J. Aranda, D. V. G. L. N. Rao, M. Nakashima, and J. A. Akkara, "Ultrafast relaxation times of metalloporphyrins by time-resolved degenerate four-wave mixing with incoherent light," J. Opt. Soc. Am. B 14, 2710-2715 (1997)