1. V.P. Zharov, V.S. Letokhov, Laser Optoacoustical Spectroscopy (Springer Series in Optical Sciences, Vol. 37) (Berlin: Springer-Verlag, 1986), 327 pp., ISBN 978-3-540-39492-1.
2. Photoacoustic Spectroscopy in Trace Gas Monitoring, Encyclopedia of Analytical Chemistry;Harren,2019
3. Real-time and historical methane CH4 levels: https://www.methanelevels.org (Cited: April 12, 2021).
4. NIST Standard Reference Database: http://webbook.nist.gov/chemistry/ (Cited: April 12, 2021).
5. High sensitivity methane analyzer based on tuned near infrared diode laser;Nadezhdinskii;Spectrochim. Acta Part A Mol. Biomol. Spectrosc.,1999