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Influence of the excited state lifetimes on the photoacoustic signal

In this paper we discuss the influence of the excited state lifetimes of molecules onto the photoacoustic signal generation. Usually, photoacoustic signal generation is performed either with nanosecond laser pulses or modulation frequencies in the MHz up to the GHz regime. The molecules’ singlet relaxation times typically lie in the order of nanoseconds, while triplet lifetimes can be considerably longer. As both time scales, i.e. the laser pulse duration used for excitation and the relaxation times, lie in the same order of magnitude there exists an influence of the excited state lifetimes onto the photoacoustic signal generation. Here, we theoretically discuss at which frequencies this influence becomes significant and what impact this has on the performance and optimum design of photoacoustic microscopes.