High power ultrafast phase-locked laser at 2060 nm from a doubly resonant optical parametric oscillator

A high-power 2-μm phase-locked femtosecond source is demonstrated by a degenerate doubly resonant optical parametric oscillator (DROPO), which is synchronously pumped by a home-built Yb:YAG Kerr-lens mode-locked thin-disk laser. A dither-free scheme, incorporating an intracavity 'parasitic' sum-frequency of signal and pump as an error signal, has been used to stabilize the DROPO at degeneracy. To our knowledge, with a pump power of 15.8 W, this system achieves the highest output power (5.6 W) and conversion efficiency (35 %) for an actively stabilized, degenerate BBO-based DROPO operating at 2 μm. The long-term stability measurement of the power over 90 minutes shows a root mean square (RMS) power noise of 0.78%, demonstrating excellent stability and reliable performance.