Photoacoustic measurements: application in plant science

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Abstract
By means of the photoacoustic effect light-induced heat can be detected, which is produced during non-radiative de-excitation following absorption of light. This paper gives an overview of the current knowledge of photoacoustic measurements. First, the principle of detection and the different instrumentations are outlined in general. Then the applications of photoacoustic measurements in plant science and in particular in photosynthesis research are described in detail, (a) The induction kinetics of intact leaves at high modulation frequencies (where the signal is only determined by heat production) are contrasted with those at low modulation frequencies (where the signal can be determined by photosynthetic oxygen evolution superimposed on the heat production). Examples for (b) the determination of time constants and for (c) the measurement of the time delay between the excitation and the detection of the signal (phase) are given. Finally, (d) photoacoustic spectra are described. These can be used to determine the pigment composition, the depth profile, the efficiency of energy transfer and the pigment activity of a sample.