## 1 Introduction  
Photoacoustic spectroscopy (PAS) is being actively developed in recent years, especially in trace gas detection [1]. As an indirect detection method based on absorption spectrum, PAS has the advantages of high detection sensitivity, good selectivity, fast detection speed, long service life [2], etc. It has been widely used in atmospheric research [3], medicine [4], the food industry [5], pollutant monitoring [6], and the power industry [7; 8]. In many scenarios, single gas detection cannot meet the needs of practical applications, and the simultaneous monitoring of multiple components is indispensable. The selection of light source is the most important element in multicomponent detection based on PAS. Commonly used light sources include low-cost mid-infrared lamps equipped with ultraarrow band filters [9; 10; 11] and single-wavelength laser arrays [12; 13; 14; 15]. These two devices need mechanical or optical accessories to accomplish wavelength switching. A more convenient alternative is to use a continuously tunable laser that covers the absorption wavelength of multiple gases [16]. For example, ethylene, acetone, and ammonia were detected in patient breath using CO\({}_{2}\) gas lasers [17]. [PERSON] et al. used a CO\({}_{2}\) laser PAS system to measure five components, i.e., carbon dioxide, ammonia, ethanol, methanol, and ethylene [18]. In 1994, [PERSON] et al. invented the quantum cascade laser (QCL) [19]. Due to its wide tunable wavelength range, QCL brought new possibilities for the development of PAS. [PERSON] et al. used DFB-QCL with a center wavelength of 4610 nm as the laser source to detect CO and N\({}_{2}\)O in the tuning range of the absorption line with high sensitivity [20]. However, QCL has problems, such as the need for a large threshold current, in operation. To solve these problems, [PERSON] [21] first reported the concept of a type II interband cascade laser (ICL). Unlike conventional semiconductor lasers, the active region of an ICL is connected in series, and this structure allows each injected electron to be reused at forward bias to emit multiple photons so that multiple gases can be detected simultaneously by a single laser when the wavelength modulation method is employed. The simultaneous measurement of methane, ethane, and propane was accomplished using a quartz-enhanced PAS (QEPAS) sensor equipped with a single ICL with a central wavelength of 3345 nm [22]. In addition to the laser source, the photoacoustic cell and pressure sensor are also important factors affecting the detection performance of PAS. Longitudinal resonance and Helmholtz resonance photoacoustic cells are usually equipped with condenser microphones. Quartz tuning forks and cantilever beams are two highly sensitive pressure sensors that are used in conjunction with a specific structure of the cell. Because the quartz tuning fork enhanced photoacoustic spectrum has a higher quality factor Q and a higher resonance frequency, it can effectively reduce low-frequency noise [23] and work at a lower pressure, which is beneficial to reducing collision broadening. However, due to the tiny arm space of the tuning fork, beam collimation is very difficult [24]. Although the cantilever sensor has higher sensitivity than the traditional capacitive microphone [25], the temperature- and vibration-sensitive features of the interferometer become important issues [26]. Helmholtz resonance photoacoustic spectroscopy has high practical application value due to its relative simplicity and low cost [27; 28]. The Helmholtz resonator is acoustically similar to a mechanical oscillator composed of two mass blocks and springs. The capillary tube connects two identical channels of the photoacoustic cell. The gas in the capillary tube moves like a piston at the resonance frequency, compressing the gas in one channel and releasing it in the other channel.