Phase mismatch
= Phase mismatch
{title2=$\Delta k$}
The residual <wave vector> difference in a wave-conversion process. For collinear <sum-frequency generation>, choose $\Delta k=k_1+k_2-k_3$. Contributions separated by $z$ then differ by <wave phase> $\Delta kz$. At <phase matching> this residual is zero. The sign convention changes some amplitude phases but not the unseeded conversion factor $\operatorname{sinc}^2(\Delta kL/2)$.