Fig. 7
From: Farey tree locking of terahertz quantum cascade laser frequency combs
Dual-comb operation with Farey tree locking. a Experimental setup of the dual-comb measurement. Comb 1 and Comb 2 are mounted on a Y-shape sample holder. The Farey tree locking of Comb 1 and Comb 2 is achieved by modulating the two lasers at frequencies with Farey fractions of 2/3 (24 dBm) and 1/1 (−20 dBm), respectively. b, c Dual-comb and intermode beatnote spectra recorded in free-running and Farey tree locking states, measured using an RBW of 10 kHz and a VBW of 1 kHz. The insets show the corresponding high-resolution spectra of frep,2 (left) and frep,1 (right), measured using an RBW of 300 Hz and a VBW of 30 Hz. d Phase noise spectra of different lines marked in (b and c). The offset frequency range is set from 1 Hz to 3 MHz
