PROBING PULSE INTENSITY (a.u.) 
Figure 2. Dependence of the yield of Chl-a variable fluorescence 
H = (F -F)/F on the intensity of probing laser pulses, measured 
max max 
for maize leaf. Maximum intensity of the probing pulses about 500 
kW/cm 2 (wavelength 532 nm, pulse duration 10 ns). 
In the case of LIF measurements on plant leaves the saturation effect may 
lead to substantial dependence of the shape of LIF spectra on the intensity of 
laser pulses. Fig.3 shows changes in spectral shape of Chl-a LIF while 
increasing the intensity of laser pulses. The explanation of the observed 
changes is more rapid saturation of fluorescence at 690 nm ( F690) in 
comparison with the component at 735 nm due to high reabsorption of F690 
(Gorbunov and Chekalyuk, 1994). Since the measurements of F690/F735 ratio 
provide the background for remote estimates of Chl-a content in leaves, as 
well as physiological state of photosynthetic apparatus (see e.g. 
Lichtenthaler, 1988,1990), the observed dependence of this ratio on intensity 
of pulsed laser excitation (Fig.4) should be taken into account for correct 
interpretation of lidar monitoring data. 
530 600 650 700 750 800 
Wavelength (nm) 
Figure 3. Changes in spectral shape of 
Chl-a LIF from maize leaf while incre 
asing the intensity of laser pulses. 
Maximum intensity of the probing pulse 
about 500 kW/cm 2 (wavelength 532 nm). 
Figure 4. Dependencies of F690/F735 
on the intensity of probing laser 
pulses for the cases of initially 
open and closed PS II RCs.