Fig. 1
From: Farey tree locking of terahertz quantum cascade laser frequency combs
Experimental setup and laser performances. a Experimental setup. A microstrip line is mounted close to the QCL to facilitate the microwave injection (modulation) and intermode beatnote signal extraction. The microwave circulator is used to isolate the transmissions of microwave injection (red line) and intermode beatnote (blue line) signals. The entire RF signal is finally displayed on the spectrum analyzer. b Light–current-voltage curves of the THz QCL measured at a heat sink temperature of 15 K in CW mode. The THz QCL ridge is 150 µm wide and 6 mm long. c Intermode beatnote map of the free-running THz QCL at a heat sink temperature of 15 K, measured with a resolution bandwidth (RBW) of 10 kHz and a video bandwidth (VBW) of 1 kHz
