SELECTIVE RESONANCE EXCITATION IN REMOTE LASER SPARK SPECTROSCOPY 
Tsipenyuk D. Yu. 
Institute of General Physics Russian Academy of Sciences 
Moscow, Vavilova 38, 117942, Russia 
Commission VII, Working Group 1 
KEY WORDS: Remote sensing, real time pollution monittoring control. 
1. INTRODUCTION 
Remote express element analysis of terrain and 
water surfaces, different kinds of aerosols and air 
with using a laser-induced plasma exited on 
samples surfaces (Tsipenyuk, 1993,  Parriger, 
1994, Belyaev, 1994) is a very perspective 
method of ecological monitoring. This method 
could give us an important information for solving 
different problems of ecology, biology, geology, 
etc. We can obtain information about the 
element composition of different kinds of terrain 
surfaces and gases. 
The rapid remote spectrochemical method of 
analysis of matter is based on a registration of 
emission spectra of laser induced plasma at the 
surfaces to be investigated. Wile plasma 
cools, optical energy is emitted at frequencies 
that are characteristic of the elements of plasma. 
In our previous paper (Bunkin, 1994) we 
presented method and technique for remote 
sensing of sea and land surfaces element 
analysis. Our experiments performed as in the 
laboratory as with the helicopter-based lidar 
system, show that it is possible clearly to 
distinguish different kinds of terrain surfaces and 
to estimate the concentrations of elements in 
the investigated objects in remote sensing 
experiments with the accuracy about 
0,0001%. 
Nevertheless, in some cases it is necessary 
to increase accuracy of measurements and 
sufficiently diminish the threshold of registration 
for certain elements and in the same time 
simultaneous multielemental analysis isn't so 
important (for example if we need to register 
only the level of the concentration Hg in water) 
For solving this problem we investigate the 
possibility of increasing the contrast of emission 
lines of certain elements by initiating plasma by 
a laser wavelength which coincides with some 
resonance transition of these elements. 
2. EXPERIMENTAL 
Experimental arrangement was based on a 
YAG:Nd laser used as a source of 1064 nm and 
714 
532 nm light and in some experiments Kr-F 
eximer laser (248.5 nm). The YAG:Nd laser 
produced 15 ns pulses at the repetition rate 1-5 
Hz. The laser pulse energy can be changed from 
1 to 100 mj. 
A horizontal laser beam was rotated by a glass 
90 prism vertically downwards. The beam was 
then focused onto the object surface by a 
high-quality telescope objective (with a diameter 
of 20 and focal length of 40 cm). In the case of 
the investigations of the salts solutions we used 
an open glass sell, 4-10 cm deep,contained the 
aqueous solution under study. It was mounted 
on an optical platform ensuring high-precision 
vertical displacement of the cell. 
Note that, provided the laser beam waist was 
more than 2 cm above the water surface, no 
breakdown was observed. In the case when the 
beam waist was more than 1 cm below the 
surface, the plasma plume did not arise, too. In 
the latter case, propagation of a laser beam in 
water was accompanied by a series of 
microexplosions. Only when plasma plume was 
produced on the water surface emission 
spectra featured well-pronounced emission lines 
of elements. 
Emission from a laser spark produced on the 
surface of the aqueous solution was detected 
at an angle of 90 with respect to the vertical. 
The emitted light was directed to a detector 
by two quartz lenses. The first lens (with a 
diameter of 6 cm and focal length of 50 cm) 
collimated the beam which was then reflected 
by mirror in the horizontal plane. The second 
lens (with diameter of 6 cm and focal length of 
25 cm) focused radiation onto the entrance slit 
of an optical detector. The parameters of the 
second lens were chosen so as to equality of 
the angular aperture of the input beam and that 
of the detector. We assume that the radiation of 
plasma plume is isotropic and the plume is 
several millimeters in size. We then find that 
approximately a 0.0001 fraction of the emitted 
light arrives at the detector input. 
The emitted light was detected by a 
multichannel spectrum analyzer, which was 
attached to a polychromator with a different 
gratings (we used several gratings from 150 to 
600 grooves/mm). The light was directed to a 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B7. Vienna 1996 
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