Apparatus for lengthening laser output pulse duration

An apparatus for use with a laser oscillator having a short duration pulse output with high spectral purity for amplifying and lengthening the pulse output without loss of spectral purity is described. The apparatus typically includes a laser amplifier and means for applying radiation from the laser oscillator to the amplifier and for reapplying a predetermined portion of the amplifier output regeneratively to the amplifier to maintain it in an amplifying condition for a period several times longer than the duration of the original radiation pulse from the laser oscillator. A timing system is provided for synchronizing the application of laser oscillator radiation to the amplifier coincident with excitation of the amplifier to a lasing condition