Broadband optical limiting and two-photon absorption properties of colloidal GaAs nanocrystals.

GaAs nanocrystals have been prepared by a mechanical ball milling technique. The optical limiting properties of colloidal ethanol suspensions of these crystals were investigated by use of a nanosecond optical parametric oscillator pumped by a Nd:YAG system. Not only at a wavelength of 1064 nm but also in the 490-670 nm visible region, colloidal GaAs nanocrystals with a concentration of 0.023 mg/mL exhibit strong optical limiting performance, which is better than that of C60 in toluene with the same linear transmittance at a wavelength of 532 nm. Two-photon absorption is regarded as the dominant mechanism for this technique, and the two-photon absorption coefficients of GaAs nanocrystals are estimated to be 5.6 and 21.1-37.0 cm/GW in the near-infrared and visible regions, respectively.