Abstract: A system for generating pulses of laser radiation which vary in frequency with time to achieve a "chirp" or frequency sweep. In a preferred embodiment, a variable-thickness, rapidly rotating disk of optically-dense material is placed in the optical loop of an injection-locked oscillator. Rotation of the disk in the optical loop of the injection-locked oscillator varies the loop optical path length, resulting in a frequency chirp. By appropriately choosing the shape of the optically dense material, a desired linear output chirp may be obtained.