A single-longitudinal-mode (SLM) double-pulse injection-seeded neodymium-doped yttrium aluminium garnet (Nd:YAG) laser was established utilizing an RbTiOPO4 electro-optic crystal to modulate the optical path of the slave resonator for generating a resonance condition. The Q-switcher was fired twice during every pump period. This enabled the laser to emit a pair of SLM laser pulses with a time separation of 200 μs. Each pulse had a pulse energy of 13 mJ at 50-Hz repetition rate, pulse duration of 20±0.5 ns, and linewidth of 30±0.3 MHz (within 2 min). The beam quality factor of M2 was <1.22. A frequency jitter of 1.4 MHz was obtained within 2 min.