Mid-IR optical parametric oscillation and second harmonic generation of repetitively pulsed output of a fibre-laser pumped Tm3+ : YAP laser in a fan-out periodically poled MgO : LiNbO3 crystal

The nonlinear optical frequency conversions of repetitively pulsed output of a 1941-nm Tm³⁺ : YAP laser pumped by a cw 1670-nm fibre laser are studied experimentally. Both mid-IR optical parametric oscillation (OPO) and second harmonic generation (SHG) are obtained in the same periodically poled MgO : LiNbO₃ crystal with a fan-out domain design by tuning the grating period and temperature. The energy conversion efficiency of the degenerate OPO at 3820 – 3970 nm exceeds 43% at a 0.5 kHz repetition rate, while the energy conversion efficiency of SHG at 970.5 nm reaches 34%.