The experimental results of a high-efficiency mid-IR laser are presented on a quasi-phase-matched single-resonated optical parametric oscillator in PPMgO:CLN pumped by a 1064 nm laser of an elliptical beam. The pump source was an acousto-optical Q-switched cw-diode-side-pumped Nd:YAG laser. The beam polarization matched the e-ee interaction in PPMgO:CLN. When the crystal was operated at 110 degrees C and the pump power was 104 W with a repetition rate of 7 kHz, average output powers of 16.7 W at 3.84 microm and 46 W at 1.47 microm were obtained. The slope efficiency of the 3.84 microm laser with respect to the pump laser was 19.1%. The M(2) factors of the 3.84 mum laser were 2.03 and 5.89 in the parallel and perpendicular directions, respectively.