Traditional beat frequency quartz-enhanced photoacoustic spectroscopy (BF-QEPAS) are limited by short energy accumulation times and the necessity of a decay period, leading to weaker signals and longer measurement cycles. Herein, we present a novel optomechanical energy-enhanced (OEE-) BF-QEPAS technique for fast and sensitive gas sensing. Our approach employs periodic pulse-width modulation (PWM) of the laser signal with an optimized duty cycle, maintaining the quartz tuning fork's (QTF) output at a stable steady-state level by applying stimulus signals at each half-period and allowing free vibration in alternate half-periods to minimize energy dissipation. This method enhances optomechanical energy accumulation in the QTF, resulting in an approximate 33-fold increase in response speed and a threefold increase in signal intensity compared to conventional BF-QEPAS. We introduce an energy efficiency coefficient K to quantify the relationship between transient signal amplitude and measurement duration, exploring its dependence on the modulation signal's period and duty cycle. Theoretical analyses and numerical simulations demonstrate that the maximum K occurs at a duty cycle of 50 % and an optimized beat frequency Δf of 30 Hz. Experimental results using methane reveal a detection limit of 2.17 ppm with a rapid response time of 33 ms. The OEE-BF-QEPAS technique exhibits a wide dynamic range with exceptional linearity over five orders of magnitude and a record noise-equivalent normalized absorption (NNEA) coefficient of 9.46 × 10⁻¹⁰ W cm⁻¹ Hz^−1/2. Additionally, a self-calibration method is proposed for correcting resonant frequency shifts. The proposed method holds immense potential for applications requiring fast and precise gas detection.

A near-infrared trace CO₂ detection system was experimentally demonstrated based on an 1,580 nm distributed feedback (DFB) laser using a cascaded integrator comb (CIC) filter-assisted wavelength modulation spectroscopy (WMS) technique and a digital lock-in amplifier (DLIA). An 1,580 nm DFB laser emitting at 1,579.1 nm was selected as the light source. A multi-pass cell (MPGC with a 30 m- long path) was adopted as the absorption cell. A DLIA was developed to extract the second harmonic WMS (WMS-2f) signal. The cascade-integrated comb filter (CICF) and the finite impulse response (FIR) low-pass filter (LPF) were combined in the DLIA to improve the performance of DLIA. Three methods of PD (Peak detection), LIA, CICF-assisted WMS, and DLIA were adopted to detect the CO₂ concentration levels and the anti-interference performance of each detection method was analyzed. The experimental results indicated that compared with the peak detection and the lock-in amplifier method of the CICF-assisted WMS and DLIA developed in this manuscript had the highest linearity and precision. When the integration time is 3s, the LOD of the system was predicted to be 0.0812 ppm. Due to the advantages of high sensitivity, a low detection limit and a rapid response, the CO₂ detection system reported in this manuscript has a good application prospect in the area of oilfield associated gases detection.