  We explore the dynamics of a system where input spectra in the optical domain
with very disparate center frequencies are strongly coupled via highly
phase-matched, cascaded second-order nonlinear processes driven by terahertz
radiation. The only requirement is that one of the input spectra contain
sufficient bandwidth to generate the phase-matched terahertz-frequency driver.
The frequency separation between the input spectra can be more than ten times
larger than the phase-matched terahertz frequency. A practical application of
such a system where the cascading of a narrowband pump line centered at 1064 nm
induced by a group of weaker seed lines centered about 1030 nm and separated by
the phase-matched terahertz frequency is introduced. This approach is predicted
to generate terahertz radiation with percent-level conversion efficiencies and
millijoule-level pulse energies in cryogenically-cooled periodically poled
lithium niobate. A model that solves for the nonlinear coupled interaction of
terahertz and optical waves is employed. The calculations account for second
and third-order nonlinearities, dispersion in the optical and terahertz domains
as well as terahertz absorption. Ramifications of pulse formats on
laser-induced damage are estimated by tracking the generated free-electron
density. Strategies to mitigate laser-induced damage are also outlined.
