Room temperature operated very small widely tunable terahertz parametric source

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We have researched a THz-wave parametric oscillator (TPO) and THz-wave parametric generator (TPG) based on the polariton mode scattering of MgO : LiNbO_3 crystals [2]. The TPO has proved to be a useful coherent THz-wave source that operates at room temperature. It is continuously tunable in the 100 to 300 μm (1 to 3 THz) range in one operation and can emit peak powers of up to several tenths mW. The difference between a TPO and a TPG is that the former has an idler cavity while the latter does not. The THz-wave linewidth of a conventional TPG exceeds 1 THz and the output is much smaller than that from a TPO. The TPG spectrum was narrowed to the Fourier transform limit of the pulsewidth by introducing an injection seeding to the idler. The THz-wave linewidth was dramatically sharpened from >1 THz to 100 MHz. A wide tunability from 0.7 to 2.4 THz (wavelength : 125 to 430 μm) was observed using an external cavity diode laser as an injection seeder. The continuous scanning and narrow spectral bandwidth of the is-TPG were verified in the absorption spectrum of low-pressure water vapor. Simultaneously, the output obtained was more stable than that from conventional TPG, TPO, and is-TPO. As far as we know, injection seeding to ns optical parametric generators (OPG) has not been reported until recently, due to the limit of parametric gain.