520 nm laser-pumped watt-level femtosecond OPO with high stability of spectra and power based on the side-of-fringe locking technique

A 520 nm laser-pumped 100 MHz LBO-based femtosecond optical parametric oscillator (fs-OPO) with high stability of spectra and power is presented, which is enabled by the side-of-fringe locking technique and whose signal wavelength can be tuned from 650 nm to 980 nm. The average powers are higher than 1 W within the nearly whole wavelength range (700–980 nm). Especially, the average power goes up to 1.8 W at 740 nm, with a conversion efficiency of 27.3%. To demonstrate the universality, three wavelengths of 740 nm, 800 nm, and 920 nm, which are called for by biophotonics, are advisedly chosen to verify the capability of the side-of-fringe locking technique for both spectral and power stabilizations. As a result, power fluctuations (in RMS) of 1.6%, 0.5%, and 1.6%, and central wavelength drifts (in SD) of 0.44 nm, 0.13 nm, and 0.19 nm, are obtained for those three wavelengths, respectively. In addition, pulse durations are measured to be 630 fs, 139 fs, and 182 fs. Those combined performances leave the possibility for long-time data acquirement in imaging experiments.