Femtosecond near-IR optical parametric oscillator with efficient intracavity generation of visible light

We present an experimental and a theoretical analysis of the operation characteristics of a femtosecond optical parametric oscillator (OPO) based on periodically poled LiNbO3 (PPLN). It provides bright visible pulses through second-harmonic generation (SHG) of the signal and sum-frequency generation (SFG) between the signal and the pump, simultaneously with the parametric oscillation in the near IR. Using a duty cycle of the poling period of approximately 56%, we achieved strong enhancement of even-order quasi-phase-matched (QPM) SHG and SFG, whereas the reduction in the efficiencies of odd-order QPM processes is negligible. Femtosecond pulses with output powers of up to 14 mW in the blue, 12 mW in the green, and 18 mW in the red were obtained for a pump power of only 480 mW. The tuning ranges extended from 460 nm to 500 nm and from 520 nm to 660 nm for SFG between the pump and signal and SHG of the signal, respectively, with at least 2-mW output power. Our work demonstrates that proper choice of the duty cycle of the poling period allows exploitation of higher-order QPM for intracavity SHG and SFG processes in PPLN OPOs.