Fig. 2: Experimental setup and results.
a Experimental setup. A cw laser is used to seed two EO combs, each consisting of an acoustic-optical modulator (AOM), an intensity modulator (IM), and an erbium-doped fiber amplifier (EDFA). The two combs counter-propagate inside a dispersion compensation fiber (DCF) for flat-top spectral broadening. After that, they are combined with a 50:50 fiber coupler and then launched, through a fiber collimator, into the gas cell. A portion of the dual combs is detected by a photodetector (PD1) for the reference. For gas detection, a membrane-in-the-middle (MIM) cavity optomechanical system is utilized. This system consists of a nanomechanical membrane, a resonance cavity and a probe laser which is locked to the cavity via the Pound-Drever-Hall (PDH) technique (Supplementary Note 2). EOM electro-optic modulator, PID Proportional-Integral-Derivative, LPF electronic low-pass-filter. b The frequency response of the nanomechanical membrane. c Recorded interferometric PA signal for 10% 12C2H2/N2. d The closer inspections of the interferometric PA signal in a measurement time window from 0.245 to 0.295 s.
