Fig. 12: Free running and mode-locked emission of a THz QCL at 3.25 THz, which were measured using injection seeding technique.

a Time resolved electric field of a free-running (black) and mode-locked (magenta curves) QCL emission from 750 ps to 1850 ps. b The zoom in of the mode-locked pulse at 1125 ps in (a). c Spectra of the free-running and mode-locked emission of the QCL through Fourier Transform of the time-resolved electric field in (a). d Phase of each lasing mode shown in (c) under free-running and mode-locked conditions, respectively