Passive laser mode locking with an antiresonant nonlinear mirror

A nonlinear mirror that is based on an antiresonant ring incorporating a nonlinear element sensitive to the polarization state of the circulating light has been developed. No phase matching of the mirror to the laser cavity is necessary, so the mirror does not need active length stabilization. Spontaneous mode locking occurs when the mirror is incorporated into a cw Nd:YAG laser. Pulses of 11-psec duration are produced at 1064 nm; two output beams at 532 nm are also generated. An analysis indicates that the primary mechanism responsible for passive mode locking is self-phase modulation in the nonlinear element.