Third-order optical nonlinearity originating from room-temperature exciton in layered compounds LaCuOS and LaCuOSe

We have studied the third-order optical nonlinearity ${\mathrm{(\chi }}^{\text{(3)}})$ of epitaxial thin films of layered compounds LaCuOS and LaCuOSe at room temperature by a spectrally resolved degenerative four-wave mixing technique with femtosecond time resolution. The ${\chi }^{\text{(3)}}$ values in both films are sharply resonant to optical absorption bands in the ultraviolet (UV) light region due to room-temperature exciton. The peak values are evaluated to be as large as ${\text{2–4×10}}^{\text{−9}}\hspace{0.17em}\mathrm{esu}$ with a fast time response of 250–300 fs. These findings indicate that LaCuOS and LaCuOSe are promising materials for emerging optical nonlinear devices that operate in the UV light region compatible for GaN-based lasers.