Jin Hua-Wei, Hu Ren-Zhi, Xie Pin-Hua, Chen Hao, Li Zhi-Yan, Wang Feng-Yang, Wang Yi-Hui, Lin Chuan. Photo-acoustic technology applied to ppb level NO2 detection by using low power blue diode laserJ. Acta Physica Sinica, 2019, 68(7): 070703. DOI: 10.7498/aps.68.20182262