Abstract
We have investigated the spectra of the third-order nonlinear susceptibility (3) in the 1D Mott insulators of the cuprate, A 2 CuO 3 (A=Sr, Ca) and the halogen-bridged nickel compounds by using the electro-reflectance spectroscopy. The maximum values of (3) in the 1D Mott insulators are 10 8 to 10 5 esu, which are much larger than those of other 1D semiconductors (10 10 to 10 8 esu) such as polysilane, -conjugated polymers and halogen-bridged platinum compounds. The enhancement of (3) is mediated by the large dipole moment between the odd and even charge-transfer excited states.