1 Terahertz - Wave Parametric Generator ( TPG ) / Pumping source 1 . 1 Injection - seeded THz - wave Parametric Generator

Coherent tunable terahertz (THz) waves were successfully generated using an injection-seeded THz-wave parametric generator (TPG) based on laser light scattering from the A1-symmetry polariton mode of MgO:LiNbO3 crystals. THz-wave spectrum narrowing to the Fourier transform limit was achieved by injection seeding the idler wave (near-infrared Stokes). This resulted in a THz-wave output approximately 300 times higher than that of a conventional TPG, which has no injection seeder. In addition, a wide tunability from 0.7 to 2.4 THz was observed using a tunable diode laser as an injection seeder. Resolution of less than 100 MHz (0.003 cm) was assured by the absorption spectrum measurement of low-pressure water vapor. This compact system operates at room temperature and promises to be a new, widely tunable THz-wave source.