Absorption cross-section determination of F2 colour centres in a LiF crystal by picosecond laser saturable absorption studies

The saturable absorption behavior of F2- color centers in LiF is studied by picosecond laser pulse excitation (wavelength λL = 1054 nm, duration ΔtL = 6 ps). The color center number density, N0, the ground-state absorption cross-section, σL, and the single-photon excited-state absorption cross-section, σex,L, are determined by numerical fitting the energy density dependent energy transmission. A decrease of energy transmission at high excitation energy densities (w0L > 1 J cm-2) is attributed to two-photon absorption of other color centers (N1 and N2 bands of F4 centers) present in the sample.