CASCADED 2ND-ORDER EFFECTS IN THE FEMTOSECOND REGIME IN BETA-BARIUM BORATE - SELF-COMPRESSION IN A VISIBLE FEMTOSECOND OPTICAL PARAMETRIC OSCILLATOR

Cascaded second-order effects are studied in the femtosecond regime in beta-barium berate by use of the Z-scan technique. Large nonlinear ph ase shifts can be obtained near the second-harmonic-generation phase-m atching condition for a Ti:sapphire laser. Solution of the nonlinear p ropagation equations for femtosecond pulses yields good agreement with experiment and also demonstrates that the description of cascaded eff ects by an effective nonlinear refractive index is no longer valid in the ultrafast domain and that these effects are less efficient for ult rashort pulses. The cascade-induced negative nonlinear phase shift in beta-barium berate is shown to be responsible for the self-compression observed in a prismless femtosecond visible optical parametric oscill ator.