KEYWORDS: Luminescence, Fluorine, Inverse problems, Chemical elements, Rhodamine, Raman scattering, Pulsed laser operation, Signal detection, Molecules, Network on a chip
Determination of photophysical parameters of atoms and molecules is one of the most important problems of fluorimetry. Such parameters are the absorption and excitation cross-sections of a fluorophore, the lifetime of its excited state, the rates of inter- and intramolecular transfer of energy. The tendency to determine as many parameters as possible, especially for multi-fluorophore systems with very high local concentration of the fluorophores, stimulates searching new approaches in fluorimetry. The possibilities of one of such approaches, which can be named "matrix method", are investigated in this paper. In this method, the elements of the matrix of fluorescence intensity values are measured. The arguments of the intensity are not only the wavelength but also the exciting radiation intensity Iexc in the range when the fluorescence saturation manifests itself, the time of the delay T of the registration moment in relation to the exciting pulse etc. The results of numerical modeling of inverse problem of determination of photophysical parameters using the elements of suggested matrix as input data and the neural network algorithms are presented. Results of development of separate sections of matrix method are shown. Experiments were performed with dye solutions and microalgae.
The problem of determination of oil pollution (OP) in nature water in situ remains topical. Laser fluorimetry as an approach to solution of this problem provides high sensitivity and the opportunity of implementation in remote mode. In this paper, we suggested to use artificial neural networks to extract small contributions of oil pollution to the band of fluorescence of nature water under UV excitation. In this study, we have expanded the set of oil pollution types, which includes different oils.
Use of pulsed lasers opens new opportunities in diagnostics of photosynthetic organisms (PSO). Due to use of pico- and femtosecond laser spectroscopy-absorption spectroscopy and fluorescence spectroscopy-was achieved large progress in study of primary processes of photosynthesis. Orders of magnitudes of many photophysical parameters were determined. In this paper it is proposed for PSO diagnostics one more laser method: method of nonlinear fluorimetry (saturation fluorimetry). This method is based on measuring of nonlinear dependence of fluorescence intensity Ifl on exciting laser radiation intensity Iexc. Because of high local concentration of pigment molecules in PSO chloroplasts dependence Ifl(Iexc) deviates from linear one at sufficiently low values of intensity Iexc≈1 kW/cm2. This effect on the one hand complicates the determination of chlorophyll a concentration from the fluorescence intensity; but on the other hand it opens up the possibility of determination of photophysical parameters.
The procedure for the determination of the non-saturated fluorescence parameter Φ0 which is proportional to concentration of chlorophyll a molecules and the photophysical parameter A has been elaborated. Parameter A is given by A=στ2γn0, where σ is the excitation cross-section of chlorophyll a (Chl a) molecules, τ is the lifetime of the excited chlorophyll a molecules taking into account all processes of a deactivation of excitation except the singlet-singlet annihilation, and γn0 is the maximum rate of the singlet-singlet annihilation. In the paper investigations were carried out with aquatic PSO-phytoplankton (PP).
There is a set of discussed questions in the study of primary processes of the photosynthesis. Solution of these problems stimulates development of new methods for determination of the photo synthetic unit photo physical parameters in-vivo. In the report possibilities of non- linear fluorimetry method in this problem are investigated. The first step requires creation of low-parametrical model of the photosynthesizing organisms fluorescence response formation. The corresponding inverse rpobe4lm can be solved for this model.
In the paper, the possibilities of classic and laser fluorimetry in photosynthesizing organisms (PSO) diagnostics are analyzed. Some special features of fluorescence of PSO excited by laser pulses are discussed. The results of research presented in the paper refer to the water PSO -- phytoplankton. However, some of them are valid for vegetation. Methods of linear and non-linear fluorimetry make it possible to determine the following parameters. (a) Fluorescence parameter (Phi) o equals Nflo/NRS, where Nflo is the photons number of photosynthesizing organism fluorescence without saturation effect, NRS is the number of Raman scattering photons from water molecules. (b) Parameter of photosynthetic activity (eta) equals Fv/Fm, where Fv and Fm are the intensities of variable and maximum fluorescence response. This parameter can be determined by the pump-and-probe technique. (c) Excitation cross-section of fluorophor (sigma) . This parameter depends on energy transfer form auxiliary pigments and reflects the group and species composition of algae. The cross-section (sigma) and other photophysical parameters of PSO can be determined by non-linear saturation spectroscopy. In principle, these parameters can be used for the diagnostics of PSO, i.e. for the determination of chlorophyll-a concentration, of photosynthesis efficiency and of phytoplankton species composition. In the paper the examples of spatial distributions of parameters (Phi) o, Nflo and (eta) obtained by ship lidar and by submersible biophysical probe are represented. The results obtained in some sea expeditions using lidars and double-flash submersible fluorimeter for phytoplankton diagnostics, are briefly analyzed.
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