Fig. 5: Channel sounding.

a Spectrometer setup where the FC for the transmitter (Tx) and the LO are referenced to the same GPS signal each via its own OCXO. b Measured spectrum of the pulsed source at 3.25 THz with a RBW of 1 Hz and a measurement time of 1 s in the configuration shown in (a). The orange line shows the Lorentz-fit with a FWHM of 80.4 Hz. c Measured FWHM of the pulsed source using different referencing methods with standard measurement deviation. The yellow curve with the triangles shows the FWHM for the unreferenced pulsed source (c.f. Fig. 3a), the orange trace with squares for referencing to the same GPS signal (Fig. 5b) with the black line representing quadratic scaling. The blue curve with circles are the results of locking to the same OCXO (Fig. 6a).