  We introduce a new regime of cascaded quadratic nonlinearities which result
in a continuous red shift of the optical pump, analogous to a Raman shifting
process rather than self-phase modulation. This is particularly relevant to
terahertz generation, where a continuous red shift of the pump can resolve
current issues such as dispersion management and laser-induced damage. We show
that in the absence of absorption or dispersion, the presented Raman shifting
method will result in optical-to-terahertz energy conversion efficiencies that
approach $100\%$ which is not possible with conventional cascaded
difference-frequency generation. Furthermore, we present designs of
aperiodically poled structures which result in energy conversion efficiencies
of $\approx 35\%$ even in the presence of dispersion and absorption.
