The terahertz (THz) region, which lies between the microwave and infrared regions, offers a wealth of untapped potential. We generated widely frequency-tunable coherent THz waves from GaP crystal pumped using continuous-wave (CW) semiconductor lasers and compared it with pulse pumping using Q-switched high-power lasers at 1-1.2 μm. THz wave generation was based on difference-frequency generation via the excitation of phonon-polaritons in GaP. CW THz waves were generated from GaP by enhancing the power density of the pumping light from semiconductor lasers. The power and phase-matched condition for THz wave generation are discussed with respect to the pumping method compared to pulse pumping. Semiconductor lasers have light power stability with a narrow linewidth. Therefore, CW THz waves can be used as a light source in high-resolution THz spectroscopy, as well as in multichannel communication.
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