Indirectly-seeded optical parametric generation in periodically poled lithium niobate

We report a technique for injection-seeding optical parametric generation (OPG) in periodically poled lithium niobate in which the wavelength of the seed is neither that of the signal nor of the idler waves; instead, it is the wavelength resulting from the sum-frequency mixing of the pump and signal waves. We show that pulsed OPG can be appropriately seeded in this way even if the sum-frequency process is not quasi-phasematched if a pulsed laser is used as a seed, and if it is quasi-phase-matched even a low power (15 mW) HeNe beam can substantially reduce the bandwidth of the generated signal wave.