MODE-LOCKING BY CASCADING OF 2ND-ORDER NONLINEARITIES

We present a comprehensive theoretical and experimental study on a new passive mode-locking technique, called cascaded second-order nonlinea rity mode locking (CSM), which exploits cascaded second-order nonlinea rities to obtain large third-order susceptibilities from an intracavit y second harmonic crystal, The nonlinear phase shift that originates i n the nonlinear crystal is converted into a nonlinear amplitude modula tion by a suitable intracavity aperture, A numerical model, based on a perturbative approach, allows to calculate the nonlinear loss modulat ion of resonators used for CSM as a function of the resonator paramete rs and of the phase mismatch, The predictions of the model are confirm ed by experiments performed on a CW Nd:YAG laser. The effects of group velocity mismatch and the limitations which it poses on the minimum a chievable pulsewidth are analyzed both experimentally and theoreticall y.