The invention is an improvement of a harmonically mode-locked ring laser of the type comprising means (12) defining an optical path, an active laser medium (15) for emitting coherent light to be transmitted along the optical path, and means (18) included in the optical path for causing the light to propagate along the path as a train of pulses having a period which is substantially equal to the transit time of light pulses in the optical path divided by an integer. The improvement is characterized in that the optical path includes a Fabry-Perot optical resonator (24) having a free spectral range substantially equal to the pulse repetition rate of the optical pulses in the ring laser. Under this condition, the Fabry-Perot resonator tends to equalize the energy, shape and width of the individual pulses.
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