Thesis subject

Projects "Developing a laser pulse method to correct for pathlenght differences in plant leaf measurements"

This is a proof-of-principle project to apply time-domain spectroscopy to the problem of light-scattering by leaves.

An important optical property of leaves is that they very effectively scatter light. This scattering increases the path-length that a ray of light takes as it passes through the leaf and essentially increases the probability that the light will be absorbed by photosynthetic pigments. The path-length increase also means that doing quantitative spectroscopy on leaves is difficult: it is relatively easy to measure the absorption of light by a leaf, but if the path-length that light takes as it passes through the leaf is not known then it is impossible to translate the absorbance into an amount of light-absorbing molecule. Measuring the path-length increase due to scattering of light is difficult, so it is also difficult to correct absorbance measurements for the path-length increase. We would like to measure scattering in a leaf using short laser pulses. If a light pulse passes through a leaf to a detector, and there is no scattering, the pulse arriving at the detector will have the same profile as the initial pulse and will arrive at a time which will be a simple function of the distance between the source and the detector. If there is scattering the pulse profile will be distorted and the flight time of the pulse will also be increased. Using near-infrared femtosecond pulses it will be possible to measure the scattering of light of pulses passing either through or along a leaf and thus obtain a measure of light-scattering at these wavelengths.