Large third-order susceptibility and third-harmonic generation in centrosymmetric Cu₂O crystal

We present what we believe to be the first experimental determination of the third-order optical susceptibility χ⁽³⁾ of bulk cuprous oxide (Cu₂O) crystals. The measured nonlinear refractive index, obtained with the Z-scan technique at 1064 nm, is n₂ = 1.32 X 10^-10 esu, while the two-photon absorption coefficient is β =5.0 cm/GW of Cu₂O. We also observe strong third-harmonic generation (THG) from Cu₂O in our detection range owing to its unique crystal and electronic structure. Considering that the first nonvanishing nonlinear term is χ⁽³⁾, this classical semiconductor could be utilized as a promising active THG medium.