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 -methoxyphenyl) tetrabenzporphyrin (ZnmpTBP), tetratollylporphyrin (TTP), cobalt tetratollylporphyrin (CoTTP) and nickel tetratollylporphyrin (NiTTP) with time-resolved degenerate four-wave mixing with the incoherent emission of a nanosecond pumped-dye laser. The experiments are carried out in the counterpropagating geometry where and are counterpropagating to one another and is at angle θ ( with respect to ). 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 for different fixed delays of the backward pump beam We observe strong signal at a second peak owing to the coherence of beams and for samples exhibiting excited-state absorption and a narrow peak corresponding to the coherence of beams and for 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.
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