A self-seeding laser comprises a slave oscillator cavity coupled to a Littman cavity that operates in a single longitudinal mode. The slave oscillator cavity comprises the following elements positioned in sequential order to provide a first beam path: an end mirror, a gain medium, a grating having a groove spacing, and an output mirror. The first beam path has an angle of incidence upon the grating, and light traveling along the first beam path is zeroth-order diffracted by the grating. A tuning mirror faces the grating, for reflecting light diffracted away from the first beam path by the grating. The tuning mirror establishes the Littman cavity. The gain medium is pumped by a pulsed pump beam. The pump beam activates a pump region within the gain medium, the pump region having a radius. The Littman cavity operates in the single longitudinal mode because the angle of incidence, the groove spacing, and the radius are adjusted so that an adjacent mode walk-off time of the Littman cavity is less than a mode build-up time of the Littman cavity. A gain in the Littman cavity is initially greater than a gain in the slave oscillator cavity; the laser is thereby self-seeded in the single longitudinal mode.