Absorption cross-section determination of F_2~- colour centres in a LiF crystal by picosecond laser saturable absorption studies

摘要

The saturable absorption behaviour of F_2~- colour centres in LiF is studied by picosecond laser pulse excitation (wavelength λ_L = 1054 nm, duration Δt_L = 6 ps). The colour centre number density, N_0, the ground-state absorption cross-section, σ_L, and the single-photon excited-state absorption cross-section, σ_(ex,L), are determined by numerical fitting the energy density dependent energy transmission. A decrease of energy transmission at high excitation energy densities (w_(0L) > 1 J cm~(-2)) is attributed to two-photon absorption of other colour centres (N_1 and N_2 bands of F_4 centres) present in the sample.