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.