Mid-Infrared Hollow-Core Fiber Based Flexible Longitudinal Photoacoustic Resonator for Photoacoustic Spectroscopy Gas Sensing oleh Zuying Xu, Tailin Li, Chaotan Sima, Yanhong Long, Xiaohang Zhang, Yan Ai, Minzhi Hong, Muqi Chen, Botao Deng, Dajuan Lv, Ping Lu