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Experimental measurement setup: (a) PGC interferometer. DFB_1310 nm, DFB laser at 1310 nm; PD, photodetector; LPF, low pass filter; DAQ, data acquisition; and F1, F2 collimators. (b) Photoacoustic system. DFB_1532 nm, DFB laser at 1532 nm; LC, laser controller; EDFA, erbium-doped fibre amplifier; CC, chopper controller; D, diaphragm; S, microphone; M, mirror; SD, signal divider; Lock-in amplifier.
