Quantum Radiophysics Division, Department of Physics
Moscow State University
119899 Moscow, Russia
The central problem in laser remote sensing of the natural organic complexes in water and on land is identification and determination of state of these complexes. Knowledge of these characteristics is important not only by itself, but it is also a necessary condition for quantitative determination of object by optical methods. Large width of fluorescence bands considerably limits possibilities of identification. Moreover, for most natural organic complexes (phytoplankton, humic and protein compounds, light oils), fluorescing centres are the same for the whole class of compounds (for example, chlorophyll-a in phytoplankton, two or three amino acids in protein compounds, one type of fluorophore of yet unknown composition in humic substance). Therefore, fluorescence bands of these complexes differ only a little, what makes identification more difficult. One way of overcoming these difficulties is known: it is increasing of spectral information volume. This includes the use of fluorescence excitation spectra, synchronous spectra, TLS-diagrams, which are difficult to record in remote mode.
In this paper, an alternative approach to this problem is proposed. This approach is based on the measurement of organic complex parameters, that are determined by intermolecular interactions and that are therefore sensitive to the structure and the state of the complex. This method is based on measurement of the curves of fluorescence saturation and on extraction from these curves of such parameters of the complexes that allow their identification and determination of their state. Such parameters are, in the first turn, the effective excitation cross section of fluorescence centers in a whole complex and the rate constant of the singlet-singlet annihilation. Both parameters depend on the process of excitation transfer in the complex and so on its structure and on the factors that influence this structure.
In this paper, approaches to the solution of incorrect inverse problems of fluorescence saturation spectroscopy are considered, evaluation of determination precision of unknown parameters of the complex is performed, requirements to a lidar for realisation of proposed method are stated.
In other papers by our group, first results obtained by the proposed method, are presented for concrete organic complexes.