Dong, JiahaoLam, Timothy T.-Y.Gray, Malcolm B.Warrington, Richard BRoberts, Edward H.Shaddock, Daniel A.McClelland, David E.Chow, Jong H.2015-12-172015-12-170003-6951http://hdl.handle.net/1885/95084We present a spectrometer based on the cavity enhanced amplitude modulated laser absorption spectroscopy (CEAMLAS) technique for measuring molecular gas absorption. This CEAMLAS spectrometer accurately measured a CO₂ absorption line at 1572.992 nm with effectively 100% measurement duty cycle. It achieved an absorption sensitivity of 5.2 × 10⁻⁹ Hz⁻¹∕² using a linear Fabry-Perot cavity with a modest finesse of ≈1000. We also used the spectrometer to perform preliminary measurements of the ¹³C/¹²C isotopic ratio in CO₂, yielding an isotopic signature δ ¹³C of −83±9‰ for our CO₂ sample.This research was funded by the Australian Research Council under the Project ID: LP100200604 and DE130101361.http://www.sherpa.ac.uk/romeo/issn/0003-6951..."Publishers version/PDF may be used on author's personal website, institutional website or institutional repository" from SHERPA/RoMEO site (as at 17/12/15). Copyright 2014 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Applied Physics Letters and may be found at https://doi.org/10.1063/1.48925352014-08-0510.1063/1.48925352016-02-24