Second-harmonic frequency-resolved optical gating
= Second-harmonic frequency-resolved optical gating
{title2=$I(\omega,\tau)=|\int A(t)A(t-\tau)e^{-i\omega t}dt|^2$}
The self-gated second-harmonic <spectrogram> has the displayed ideal form. Its delay marginal is proportional to the <intensity autocorrelation> by the <Parseval identity>. Absolute time and <wave phase> are undetermined; $A(t)$ and $A^*(-t)$ also give the same record. Finite crystal acceptance and <spatial walk-off> modify the ideal gate.