Time Resolved Fluorescence Of Vegetation - Excitation Intensity Analysis

This article describes time-resolved measurements of the laser induced chlorophyll fluorescence emission of vegetation in laboratory and from remote. In the view of a possible application of this technique for the remote detection of plant stress, the influence of the exciting laser pulse intensity on the overall fluorescence decay was studied. All the intensity measurements have been performed using picosecond laser excitation and a streak camera detection system. For calibration a single photon c0untin.g apparatus has been used. The fluorescence decay of plants in steady state conditions of photosynthesis is characterized by a medium lifetime of about 0.35-0.40 ns at low intensity of the 50 ps 355 nm excitation pulse. Using an excitation pulse intensity above 1014 photons per cm2 the lifetime in the above mentioned conditions decrease significantly. This shortening is interpreted in terms of exciton annihilation.