Nonlinear optical coherence length
= Nonlinear optical coherence length
{title2=$\ell_c=\pi/|\Delta k|$}
The distance over which a constant <phase mismatch> accumulates <phase difference> $\pi$. In unseeded, undepleted <sum-frequency generation>, the generated <intensity> first reaches a maximum at this length and returns to zero at $2\ell_c$. This length concerns relative phases of interacting waves, rather than the temporal <optical coherence length> of one source.