Anomalies in the fluorescence of petroleum products excited by laser radiation

This paper describes how the fluorescence intensity of a number of petroleu m products depends on the energy density of laser pumping within the limits from 10(-8) to 10 J/cm(2). It is established that, for pump energy densiti es of about 1 J/cm(2), the quantum yield of the fluorescence increases inde finite sections of its spectrum. This effect is treated as the appearance o f a collective interaction of radiative centers that allows the Fluorescenc e to compete with longitudinal relaxation processes. The width of these spe ctral sections determines the degree of inhomogeneity of the fluorescence s pectrum. Their position is an individual characteristic of the petroleum pr oduct, and, in combination with data on the quantum yield, allows it to be identified. It is shown that measuring the fluorescence intensity for weak pumping fields, which is especially important for remote probing, makes it possible to determine the thickness of the petroleum film if the background illumination level is used as a reference signal. (C) 1999 The Optical Soc iety of America. [S1070-9762(99)00805-2].