Two-photon absorption of matrix-free Ge nanocrystals

The authors demonstrate that solution synthesized Ge nanocrystals (NCs) display a highly nonlinear optical absorption. The Ge NCs with an average diameter of 5±2nm are synthesized from germanium(II) bis(trimethylsilyl)amide with hexadecylamine surfactants at 300°C and 1atm in argon atmosphere. The resulting Ge NCs in a powder form are then dispersed on a silica glass substrate. Femtosecond pulses at 820nm wavelength from a mode-locked Ti:sapphire laser are used to measure a two-photon absorption coefficient of the deposited Ge NCs. The calculated coefficient ranges from 1190to1940cm∕GW.