Fig. 1: Illustration of QEMR-PAS.

a Dual comb interacts with gas molecules and generates multiple heterodyne acoustic tones. The acoustic tone resonant with the QTF is enhanced and then converted into an electrical output by the QTF. b Conversion from an optical dual comb (on top) to an audio frequency comb (on bottom). An example of down-conversion is demonstrated (in the middle) where the carrier represents the optical frequency, and the envelope represents the modulation frequency in optical power. The red comb line in the audio frequency comb corresponds to the resonance frequency of the QTF. c QEMR-PAS utilizes a QTF to detect the sound wave generated by the photoacoustic effect. The red teeth in the audio frequency combs represent the components within the QTF response bandwidth at the different \({f}_{0}(t)\), and the gray shadow is the area of the QTF frequency response