Femtosecond kerr-lens mode locking with negative nonlinear phase shifts

摘要

A Kerr-lens mode-locked Cr:fosterite laser 15 operated with negative nonlinear phase shift. The nonlinear phase shift is induced by the cascade x⁽²⁾ x⁽²⁾ process in a lithium triborate crystal. Employing the cascade process at large phase mismatch produces a nearly linear frequency chirp. Transform-limited pulses as short as 60 fs are generated with positive cavity dispersion.