Absolute and relative determination of CEP from the interference of multiple low-order harmonics

In this contribution the authors provide simple considerations that the absolute CEP calibration does not actually require access to the temporal envelope because, following from the Fourier phase shift theorem, the very same phase is the common phase offset of all spectral components of the pulse. Therefore, the challenge is to find a way to calibrate this common (spectral) phase via nonlinear spectral interference.