Laser-induced fluorescence imaging of plants using a liquid crystal tunable filter and charge coupled device imaging camera

We developed a laser-induced fluorescence imaging system for plant monitoring use, with which it was possible to make an image at any wavelength between 430 and 750 nm. The excitation source for the fluorescence was a cw ultraviolet laser diode with 398 nm, and the detector was an image-intensified charge coupled device. A liquid crystal tunable filter was used as the fluorescence wavelength selection device. All of the system performance including the wavelength tuning was electrically controlled, so that it could be operated with no mechanical vibration noise. The fluorescence images of a coffee tree leaf obtained at 440, 530, 685, and 740 nm clearly showed a distribution pattern of the fluorescence intensity over the leaf. The pattern reflected the different physiological statuses of the plant. Advantages of the imaging system were experimentally discussed on a point of detection of inhomogeneous physiological activities over a plant leaf. (c) 2005 American Institute of Physics.