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Time-Resolved Femtosecond Degenerate Four-Wave Mixing in LiNbO3:Fe,Mg Crystal

Forward degenerate four-wave mixing (DFWM) processes are investigated with a femtosecond pulsed laser in lithium niobate crystal doubly-doped with magnesium and iron (LiNbO3:Fe,Mg). The pulse energy dependence reveals a pure third-order nonlinear response, and the third-order nonlinear susceptibility χ(3) in the material is evaluated to be 4.96×10−13 esu. The time-resolved DFWM process shows a response time of χ(3) shorter than 100 fs, which is due to the nonresonant electronic nonlinearities. Our results indicate that LiNbO3 crystals have potentials for ultrafast real-time optical processing systems, which require a large and fast χ(3) optical nonlinearity.