Fig. 1. Structure of dual pass off-beam resonator tube

Fig. 2. Numerical simulation result for the size and position of the AmR

Fig. 3. Infrared absorption spectrum of 1 000×10^-6 C₂H₂ and 1%H₂O based on HITRAN database

Fig. 4. Modeling and image of acoustic detection module of miniature QEPAS system

Fig. 5. Schematic of miniature QEPAS system

Fig. 6. Waveform diagram of the 2f-signal measured at 200~1 000×10^-6 C₂H₂ concentration

Fig. 7. Linearity analysis of the miniature QEPAS system

Fig. 8. Background noise measurement results of miniature QEPAS system

Fig. 9. Long-term stability analysis of miniature QEPAS system