  We report on important influence of single domain wall (DW) of electrically
poled ferroelectric crystal on parametric processes via Cherenkov-type phase
matching. It shows that the effective nonlinear polarization is confined in DW
and its phase velocity can be modulated when incident light is off domain
wall's direction. These effects lead to novel Cherenkov second harmonic
generation (CSHG) which has no analogue in bulk ferroelectrics. Complex
DW-modulated parametric process via Cherenkov-type phase matching, such as
Cherenkov sum frequency generation (CSFG), is also demonstrated in DW. We
propose that nonlinear coefficient in DW is significantly enhanced.
