In this paper, an acousto-optic (AO) Q-switch based on α-BaTeMo2O9 (α-BTM) crystal is designed and further applied to generate a laser pulse at 639 nm for the first time. The α-BTM AO Q-switch demonstrates a large diffraction angle of 0.93° and a high diffraction efficiency of 85% at 639 nm. In the experiment, a maximum AO Q-switched output power of 362 mW is achieved at a repetition rate of 30 kHz, under a maximum absorbed pump power of 3.60 W, corresponding to a slope efficiency of 15.2%. With transmittance of T = 3%, the shortest Q-switching pulse width of 54.7 ns is generated at a repetition rate of 1 kHz. Meanwhile, the beam quality factor M2 of the above laser is measured, presenting the magnitude of 1.14 at both x and y directions. Our findings indicate that α-BTM AO Q-switch could act as an excellent switching device at 639 nm which may help to explore potential applications in the visible field.
