Longitudinal profile of luminescent tracks induced by laser filaments in LiF crystal

Filamentation of femtosecond laser pulses in a lithium fluoride crystal LiF leads to the formation of luminescent tracks from color centers, such as F2 and F+3 centers. Track formation is used to create optical microstructures in the bulk of a crystal, for example, microwave guides. An increase in the length of the tracks is observed under the action of series of repeated laser pulses. In this work, using numerical simulation, it is shown for the first time that the nonlinearity of the dependence of the observed luminescence intensity of color centers on their concentration plays a role in the visible prolongation of tracks along with other known mechanisms.