Useful nonlinear phase shifts can be produced in cascaded quadratic processes. The issues that arise in the extension of cascade nonlinearities to the femtosecond regime are outlined in this paper, and initial applications of the cascade phase shifts to femtosecond pulse generation and propagation are reviewed. The results demonstrate that the cascade phase shifts offer unique properties, and in some cases pulse-shaping techniques based on cascade nonlinearities have potential to offer

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... al performance improvements over existing approaches.