Femtosecond optical parametric oscillators based on periodically poled lithium niobate

We describe two configurations of collinearly pumped femtosecond optical parametric oscillator based on periodically poled lithium niobate and tunable in the infrared from 975 nm to 4.98 mu m. Maximum output powers of 240 mW for the signal and 106 mW for the idler were recorded with 25 mW of average power measured at 4.88 mu m. An overall conversion efficiency of 35% and slope efficiencies for the signal of 46% at a wavelength of 1.04 mu m and 70% at 1.11 mu m were measured. Interferometric autocorrelations of the signal and idler pulses at various wavelengths within the tuning range have been obtained and imply nearly transform-limited pulse durations of about 140 fs for the signal and about 190 fs for the idler.