摘要： Laser photo-acoustic spectroscopy (LPAS) is a highly sensitive and selective method for trace gas analysis. One of the most advanced LPAS techniques is cantilever-enhanced photo-acoustic spectroscopy (CEPAS), which can reach down to low-ppt and sub-ppt level trace gas detection sensitivities with high power lasers [1,2]. The selection of wavelengths and tunability of high power narrow linewidth lasers is, however, limited. They are also rarely suitable for field deployable analysers, which would require a small and robust form factor. An alternative approach, potentially overcoming these weaknesses, is to build up the optical power of a standard distributed feedback diode laser (DFB) or a quantum cascade laser in an external optical cavity [3,4]. Here, we show the first demonstration of enhancing the sensitivity of a CEPAS sensor with an external optical build-up cavity, a technique which we call the cavity-enhanced CEPAS (CE-CEPAS). We achieve an unprecedented normalised noise equivalent absorption (NNEA) value of 1.75×10-12 W cm-1 Hz -1/2. In our work, the NNEA results in 75 ppt noise equivalent concentration for C2H2 with a 10 s integration time in the 1530 nm wavelength range. Compared to standard CEPAS, the detection limit is better by a factor of 100, which corresponds to the power build-up factor (BUF) of our cavity. With operation in the near-infrared region, we benefit from the highly reliable and inexpensive components of the telecommunications industry, while achieving a detection sensitivity that is comparable to the state-of-the-art results obtained in the mid-infrared region, where the molecular absorption lines are typically two orders of magnitude stronger.