Mode locking with linear and nonlinear phase shifts

The mode locking of a cw Nd:YAG laser by translation of one of the cavity mirrors is reported. The mode-locking effect is greatly enhanced when an intracavity nonlinear KTP crystal is used. Stable pulse trains with a 60-ps average pulse width are obtained. Theoretical analysis shows that the combined effect of linear phase shift imposed by the moving mirror and the nonlinear phase shift in the Kerr medium gives rise to a saturable-absorber-like behavior in a homogeneously broadened laser. The theory agrees well with the experimental results as well as with results obtained with a Ti:sapphire laser.