Mode-locking of a femtosecond Cr:forsterite laser with negative nonlinear phase shifts generated by /spl chi//sup (2)/:/spl chi//sup (2)/ cascading

Summary form only given. Recently, there has been a resurgence of interest in the effective third-order nonlinearity that arises from the cascading of /spl xi//sup (2)/ processes. Applications of the cascade nonlinearity include the mode-locking of lasers, and this has been proposed and demonstrated with picosecond pulses. Previous workers noted that the phase shift produced by the cascade process is modulated significantly owing to group-velocity mismatch and saturation. Here we show that undistorted frequency chirps can be produced in the cascade process, and describe the first KLM laser operating with an overall negative nonlinear phase shift.