Narrow linewidth tunable THz signal radiated by photomixing: Coupling a unitravelling carrier photodiode and a two-axis dual-frequency laser

A narrow linewidth THz source is reported. A beatnote provided by a dual-frequency laser is sent into a unitravelling carrier photodiode, and radiated by a transverse-electromagnetic-horn antenna. The emitted THz signal is detected by a subharmonic mixer coupled to an electrical spectrum analyzer. The measured linewidth is better than 30 kHz and tunable from DC to 770 GHz with a minimum 30 dB dynamic range.