931 
lents: so-called 
>nes (see, e.g. 
functional state 
lgly depends on 
dive) up to 2-4 
VIVO 
primary photo- 
is often under- 
lodel describing 
anosecond laser 
his model takes 
synthetic units, 
on of excitons, 
RCs caused by 
?92). 
the model: PIQ, 
:he intermediate 
PS II RC). The 
' respectively. 
s the effective 
0 account the 
rophyll-c, and 
oncentration of 
ition of Chl-a 
of RCs in the 
deactivation of 
- the rate of 
on in close RC; 
I (and yield 
r 1 
’constant’ and 1 
1 of theoretical 
and experimental data has proved adequacy of the model. In addition, this 
allowed to determine the relationship between the rates of exciton capture by 
PS II RC for different states of the RC (Bunin et al., 1992). 
4. - SATURATION OF LIF FROM CHLOROPHYLL IN VIVO 
The consequence of practical importance is nonlinear dependence of LIF 
intensity (and LIF yield) on power of laser pulses ("saturation" of 
fluorescence). In the case of in vivo Chl-a fluorescence this effect is 
observed even at relatively low levels of laser irradiance (I = 10 kW/cm“ 2 ). 
The saturation of LIF from in vivo Chl-a is caused by a number of mechanisms, 
main of which in the case of excitation by nano- and picosecond pulses is 
singlet-singlet annihilation of excitons within the light-harvesting complexes 
(see e.g. Bunin et al., 1992). 
Effect of LIF saturation should be taken into account for estimating the 
practically important variables such as: 
- phytoplankton Chl-a concentration in water from measurements of Chl-a 
fluorescence normalized to water Raman scattering (Fig.l); 
- photosynthesis efficiency of algae and leaves from measurements of 
Chl-a variable fluorescence n = (F -F)/F (see Fig.2 and (Chekalyuk and 
max max 
Gorbunov, 1994b,c; Gorbunov and Chekalyuk, 1994)); 
- Chl-a content in leaves and their physiological status on the base of 
measurements of the Chl-a fluorescence ratio F690/F735 (Fig.3,4), as well as 
of other fluorescence ratios as the blue/red one F440/F690, green/red 
F530/F690; 
- time of Chl-a fluorescence decay by means of picosecond time-resolved 
measurements (Schmuck et al., 1991). 
Fig.l represents a typical curve of phytoplankton Chl-a fluorescence 
saturation, measured remotely by shipboard lidar (from a distance of 15 m.). 
According to our field lidar measurements, the decrease in Chl-a fluorescence 
yield due to LIF saturation may reach 2-3 times in comparance with its 
’unsaturated’ value, that leads to corresponding distortion of fluorescent 
lidar data. 
Figure 1. Saturation curve of phytoplankton Chl-a fluorescence 
measured remotely by shipboard lidar (from a distance of 15 m.). 
Maximal values of water Raman scattering, used as a measure of 
laser excitation intensity, corresponds to laser intensity 100 
kW/cm 2 (wavelength 532 nm, pulse duration 10 ns).