Fig. 3: Spectrum of unreferenced pulsed THz source.

a The FC is free-running during the spectrum analyzer measurements while the LO of the receiver (Rx) is referenced to GPS. b Acquired spectrum of the pulsed THz source at a frequency of 300 GHz with a resolution of 1 Hz. The inset shows the peak of the signal and the determined full-width half-maximum (FWHM) linewidth of 1.7 ± 1.3 Hz.