The saturable absorption behavior of F2− color centers was studied by means of ps laser pulse excitation (1054nm, 6ps). The color center number density, the ground-state absorption cross-section and the single-photon excited-state absorption cross-section were determined by numerically fitting the energy density-dependent energy transmission. A decrease in energy transmission at high excitation energy densities (>1J/cm2) was attributed to 2-photon absorption by other color centers (N1 and N2 bands of F4 centers) in the sample.

Picosecond Laser Saturable Absorption Studies of F2- Color Centers in LiF Crystal. O.Lammel, A.Penzkofer, T.Tsuboi: Optics Communications, 2002, 206[4-6], 389-400