Two-photon absorption of Sin (n = 3-10) clusters compared with Si bulk

► TPA properties of the Sin (n = 3-10) clusters were investigated by using the sophisticated response approach. ► TPA coefficients of the Si clusters are systematically smaller than those of Si bulk for 800-2200 nm. ► TPA coefficients of the Si clusters as well as Si bulk increase with a decrease of the input light wavelength. ► Channel of double resonance results in large TPA coefficients of the Si clusters in the visible range.