We have achieved efficient simultaneous intracavity doubling of the signal frequency and sum-frequency generation between the signal and the pump in a periodically poled femtosecond optical parametric oscillator pumped by a Ti:sapphire laser. The responsible mechanisms are second-, third-, and fourth-order quasi-phase matching (QPM). An poling duty cycle permits efficient even-order QPM. Femtosecond pulses tunable in the visible were generated with a total efficiency of more than 8% for only 480-mW pump power at 80 MHz. Optimization of the poling duty cycle can improve the efficiency further.
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