ИСТИНА

Formation of fluorescent color centers in certain crystals under the action of femtosecond laser pulses makes it possible to create permanent fluorescent traces of filamentation in the media. In this work we study filamentation in LiF crystals. LiF samples were irradiated with single pulses and trains of pulses. Excitons and electron-hole pairs, induced by laser radiation, are transformed into stable fluorescent F-aggregate color centers, in particular F2 and F3+ centers. Spatial distribution of F2 and F3+ color centers was then studied with fluorescence microscopy. The shape of the fluorescent channels was compared to result of numerical simulations of filamentation. The mathematical model accounts for the nonlinearity of fluorescent color centers formation from electron-hole plasma and saturation of concentration of centers with the accumulation of the number of pulses. In particular, the model describes prolongation of traces of filamentation with accumulation of number of laser pulses.