Spatial walk-off
= Spatial walk-off
Loss of spatial overlap between interacting finite beams because their <energy flux> directions differ. In an anisotropic crystal, the direction of the <Poynting vector> need not coincide with the <wave vector>. For beam radius $w$ and relative walk-off angle $\rho$, an overlap length is of order $w/|\tan\rho|$. A full conversion calculation also includes beam profiles, <diffraction> and <phase mismatch>.