Light-harvesting for photosynthesis within leaves depends on pigment concentrations as well as the light transport properties of mesophyll cells. Despite the fact that the light transport properties of leaves are an integral part of their form and function, there is little quantitative information about the biophysics of light transport through leaf tissue. One of the most important biophysical parameters is the average pathlength that a photon travels within a leaf, which indicates the time over which a photon resides inside that leaf. The longer the lifetime, the greater the probability of absorption for photosynthesis. The wide variety of leaf anatomy and the striking changes that occur when leaves develop under high vs. low light may be adaptations that are directed toward the control of light capture by modification of light scattering properties of the leaf tissues. This project proposes to construct instrumentation that utilizes ultrashort laser pulses to measure the average transit time and transit time distribution of the light scattered and transmitted through thin leaves of various plant species and through leaves grown under different light environments. The average transit time represents the average lifetime a photon resides in the leaf. This instrumentation uses a wavelength of light not absorbed by photosynthetic pigments so that the light scattering effect can be measured exclusively. The proposed instrumentation will allow sensitive photon transit time measurements with femtosecond (10-15 second) temporal resolution; thus allowing measurements on typical leaves.
