3. Non-linear measurement methods

The above-mentioned linear measurement methods are relatively simple to implement, and enable precise determination of the spectral phase of the pulse to be characterized. In view of the high sensitivity that their linear nature confers, we recommend their use whenever a suitable reference pulse is available. However, we still need to characterize the reference pulse, which requires a self-referencing characterization method. As we established above, in the absence of a non-stationary mechanism, a self-referential measurement of the pulse will only be possible using a non-linear optical process