Enhanced third-order nonlinear optical susceptibilities of α-FeOOH nanorods

α-FeOOH nanorods (NRs) with diameters varying from 12 nm to 25 nm were prepared by colloid chemistry method, and their third-order nonlinear susceptibilities (χ(3)) were investigated by Z-scan technique. Both the real part and imaginary part of χ(3) increase with increasing the NRs’ size in the near resonant and transparency region. χ(3) of α-FeOOH NRs with the diameter of 25 nm can reach 7.7 × 10−11 esu in the near resonant region, which is almost 16 times of that of the corresponding bulk. The quantum confinement effect and local field effect make the dominant contribution to the nonlinear enhancement.