Er:YAG 2.94-mu-m lasers and Er:YLF 2.81-mu-m lasers were actively mode locked, with TeO2 as the acousto-optic modulator. The Er:YLF crystal generated shorter and more stable pulses, whereas the Er:YAG had a higher slope efficiency of 0.8% in free-running operation. Mode-locked pulse durations of < 700 ps were obtained with Er:YLF by applying 4 W of electrical driving power to the LiNbO3 transducer.