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Tunable THz source based on frequency conversion in quasi-phase-matched GaAs

We report a new highly efficient source of frequency-tunable (0.5-3.5 THz) narrow-bandwidth terahertz wave packets with up to 1 mW average power, based on parametric down-conversion in quasi-phase-matched GaAs. Different lasers were employed as a pump source, including femtosecond OPA/DFG system (wavelength range 2-4μm), Tm-fiber femtosecond laser (wavelength ~2μm), and near-degenerate synchronously-pumped picosecond OPO system with extra- and intracavity THz generation. We prove experimentally that the optical-to-terahertz conversion efficiency is fluence-dependent, with the scaling factor being the same for femtosecond (optical rectification) and picosecond (difference frequency generation) pump pulses, with optical-to-terahertz conversion efficiency on the order of 0.1% per μJ.