Optical frequency translation of pulses from a mode‐locked laser is described and demonstrated experimentally. The laser beam is passed through a crystal of LiNbO3whose refractive index is made to change sinusoidally at the mode‐locked laser round‐trip frequency (56 Mc/sec). A Doppler shift of the laser light results. Shifts of ±2.4 Gc/sec have been observed. The scheme may be capable of producing shifts as large as ±1000 Gc/sec.