A technique for Mode locking a laser, exploiting nonlinear self-focusing.

Kerr Lens mode locking (KLM) is a technique of Passive Mode Locking a laser, using an artificial saturable absorber based on Kerr lensing in the Gain medium. The latter effect causes a reduction of the beam size for high intensities. This can effectively act like a FAST saturable absorber when it leads to a better overlap of Laser and pump beam, or when it reduces the optical losses at some aperture.

KLM has enabled the generation of the shortest Pulses with durations down to about 5 femtoseconds in Ti:sapphire lasers. Its strength lies in the very fast response and the fact that no special saturable absorber medium is required. The main disadvantage is the need to operate the laser close to a stability limit of its resonator, because otherwise the Kerr lensing effect is too weak. As a consequence, long-term stable operation is difficult to achieve, and the Resonator design is a difficult task. Also, reliable self-starting mode locking is often not achieved.