We fabricated a periodic domain structure in a 0.5 mm thick slab of LiTaO3crystal by applying an external pulsed field at room temperature. Using a pulse dye laser with a pulsewidth of 8 ns and a repetition rate of 10 Hz, third‐order quasi‐phase‐matched second‐harmonic blue‐light generation is demonstrated by free propagation of a 862.6 nm fundamental Gaussian beam in a 4 mm long LiTaO3slab, with a single pulse energy of 0.072 mJ and an energy conversion efficiency of 5.7%. ©1995 American Institute of Physics.