m in Hg. 1, where re- 
h those from a Green 
' the species. The phy- 
it 690 nm 740 nm re 
lish between the two 
tration (c > 1 g/1) usu- 
>n emitted by the pig- 
n detection, we meas- 
ge. Significant results 
jreen species, respec- 
edally in the case of 
R 0 (660)/RamanlH30) 
j." LI TH R,( 690)/Raman( H 2 0) 
c? 5 
j 
-0.40 J 
v : 
o ; 
~ 0.20 ] 
.*4 
U 8 " 
Concentration (mg/1) 
Fig. 3 - Algae concentration measurements on different samples upon excitation @ 308 nm, detection 
channels as in the labels: (a) Spiiulina Platensis in a 180 cm high water column, (b) Tetraselmis 
Suedca in a 30 cm high water column. 
been suggested by a Russian group [10]. This new technique for monitoring the photosynthetic activity, based 
on chlorophyll fluorescence exdtation induced by two lasers, has been set up in our laboratory and is presented 
here. 
According to this idea, it should be possible to stimulate a sudden and strong variation of the bio 
chemical state of the photoreceptors by using a suitable light exdtation, so that the laser induced fluorescence 
just before and after such a stimulation should carry a differential information on the effidency of light energy 
conversion. 
500 
al- 
utions of the consid- 
iluted algae solutions 
ncreasing algae con- 
are shown in Hg. 3, 
orophyll R, band in- 
Tetraselmis. 
mined in laboratory 
close to 2 pg/1, thus 
is been used so far as 
oratory and field ex- 
lo actually affect this 
rement which some- 
temal fadors, has 
Fig. 4 - Probe and pump-probe fluorescence spectra: a) Tetraselmis Suidca, chi cone. = 6.9 mg/1; 
b) Sprirulina Platensis, chi cone. = 4.6 mg/1; Date 23 Sep. 1993, pump-probe delay = 45 ps.