Nonlinear optical response during the electron transition process originated from 3D spin-orbit splitting in NiO...

NiO, a 3d transition-metal oxide with the strong electron correlation, has attracted great physical attention due to the spin-orbit splitting of 3d electrons. By taking advantage of electron transition process originated from 3d spin-orbit splitting, it may be applied to many photonics areas by linear or nonlinear optical response. To further broaden the photonics applications of NiO, we originally explore the nonlinear optical response, saturable absorption, during the electronic transition due to 3d spin-orbit splitting under a strong optical field and successfully applied in the ultrafast photonics as a mode-locker for the generation of visible laser pulses, which is the result of dynamic balancing process by the electron transition arising from ground state (³A_2g) to excited state (¹E_g) of spin-orbit splitting in the Ni²⁺ 3d configurations. With the NiO nanosheet film for saturable absorption, we experimentally realize a pulsed visible laser at a wavelength of 640.3 nm for the first time to our knowledge. These results indicate that the study of electron transition process generated by 3d spin-orbit splitting in 3d transition-metal oxides should be helpful for the development of ultrafast photonics and related devices design.