High efficiency, widely tunable, green-laser-pumped BiB 3 O 6 femtosecond OPO with noncollinear phase matching in the yz plane

A femtosecond optical parametric oscillator (fs-OPO) based on type-I (o→e + e) noncollinear phase matching in the yz plane of bismuth triborate (BIBO) crystal is demonstrated, which breaks the bandwidth (700–1900 nm) limit set by collinear phase matching. The pumping source is provided by the second-harmonic (SH, 520 nm) wave of a homemade 1040-nm Yb:fiber femtosecond laser with a pulse duration of 177 fs and a repetition rate of 100 MHz. Experimentally, the wavelengths can be tuned from 626 nm to 3051 nm (626–1026 nm for signal and 1067–3051 nm for idler) by adjusting the angle of the BIBO crystal, which, to the best of our knowledge, is the widest wavelength tuning range for any BIBO-based femtosecond OPO. At the wavelength of 713 nm, the highest average power of 1.3 W is obtained, with a conversion efficiency of 37.1%. If both signal and idler powers are counted in, the total efficiency is 52%, which is a new benchmark. In addition, the compressed pulse duration is measured to be 108 fs at 788 nm, with a time-bandwidth product (TBP) of 0.46. The beam quality factors M 2 of 788 nm laser are measured to be M x 2 =1.38 and M y 2 =1.18, respectively.