Remote laser diagnostics of oil films on water surface using fluorescence saturation spectroscopy

    V. V. Chubarov, V. V. Fadeev, .S. M. Glushkov, V. A. Shaporev
    Quantum Radiophysics Division
    Department of Physics
    Moscow State University
    119899 Moscow, Russia

    Oil identification is the core problem of the remote diagnostics of oil films. This problem is extremely important for both umpire analyses, and the oil film thickness determination by any optical methods. There are many different fluorescence methods for oil product identification in water environment. Among these methods, the most efficient one for the purposes of identification is the method of Total Luminescence Spectra (TLS). However, its application in a remote regime is extremely difficult, so there is a high demand for alternative techniques. As one such alternative technique, we propose the fluorescence saturation spectroscopy that seems to be very promising.

    In this paper, we consider the method of fluorescence saturation spectroscopy that allows us to measure a set of parameters depending on the composition, structure and intermolecular interactions in complexes. This set can also include such parameters as the effective excitation cross section of fluorescing centres in the complex, the singlet-singlet annihilation constants, etc. These parameters provide more complete information for detailed identification of an object under study.

    However, the creation of a laser spectrometer for the fluorescence saturation spectroscopy, especially for using in the remote regime, was associated with the fulfilment of rather difficult requirements. To conduct measurements, one should rigidly control both temporal (on the nanosecond scale) and spatial distributions of a pulsed laser radiation over pumping laser spot directly at the object under study. Furthermore, the laser spectrometer should be capable of measuring the absolute intensity of laser radiation in the same laser pulse.

    In this paper, we propose a scheme of laser spectrometer for the fluorescence saturation spectroscopy. Also, some preliminary results of model experiments on the remote identification of oil films on the distilled water surface are reported. This identification allowed us to realise the both early offered methods of the oil slick thickness determination: 1) the method of calibration the fluorescence oil film signal on the Raman backscattering (RS) signal from the water; 2) the method of the differential absorption of two RS signals from the water by using the biharmonic laser excitation of the oil slick.