Second-harmonic coherence length
= Second-harmonic coherence length
{title2=$L_c=\pi/|\Delta k|$}
The length over which the harmonic and its quadratic source accumulate a relative <wave phase> of $\pi$. For nonzero <second-harmonic phase mismatch>, $L_c=\pi/|\Delta k|$; the first output zero of the uniform undepleted model occurs at $2L_c$. This is a propagation mismatch length, distinct from the pump's <optical coherence length>. It diverges as perfect <phase matching> is approached.