A device for the determination of the microsecond component of the in vivo chlorophyll fluorescence induction kinetics

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Abstract
A device for the measurement of the in vivo chlorophyll fluorescence induction kinetics at the wavelengths 685 nm and 730 nm is described. The excitation light provided by a He-Ne laser is switched by an acousto-optic modulator (Bragg cell) which achieves a rise time of the excitation light intensity Ie of 0.3 mu s. A combination with an additional mechanical shutter ensures that Ie is constant within 11% during the total measuring time of 5 min. Data acquisition is accomplished by a transient recorder with a time resolution of 10 mu s and a computer with a sampling rate adjusted between 5000 s-1 and 5 s-1. The initial fluorescence intensity F0, the inflection point Ip (during the rise of the fluorescence at the beginning), the maximum intensity Fp and the final steady-state value Fs can be evaluated with high accuracy, so additional information is provided to estimate the efficiency of the photosynthetic system.

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