Tunable terahertz-wave parametric oscillators using LiNbO3 and MgO:LiNbO3 crystals

Coherent tunable terahertz waves were generated successfully using a terahertz-wave parametric oscillator (TPO) based on laser light scattering from the A(1)-symmetry polariton mode of LiNbO3. This method has several advantages, such as continuous and wide tunability (frequency: 0.9-3.1 THz), a relatively high peak power (more than a few milliwatts), and compactness of its system (tabletop size). In addition, the system simply requires a fixed-wavelength pump source, and it is easy to tune. This paper deals with the general performance of this terahertz-wave source using the prism output-coupler method as well as the development and applications of the system. Its tunability, coherency, power, and polarization were measured, and this tunable source was used for terahertz spectroscopy to measure the absorption spectra of LiNbO3 and water vapor. Also, the use of MgO-doped LiNbO3 (MgO:LiNbO3) in our terahertz regime, as well as its far-infrared properties, is described. We found that the MgO:LiNbO3 TPO is almost five times more efficient than the undoped LiNbO3 TPO, and we have proven that the enhancement mechanism originates from the enhanced scattering cross section of the lowest A(1)-symmetry mode in a spontaneous Raman experiment.