Simultaneous detection of multiple gas concentrations with multi-frequency wavelength modulation spectroscopyZhirong Zhang, Hua Xia, Fengzhong Dong, Tao Pang, Bian Wu, Pengshuai Sun, Gaoxuan Wang and Yu WangEPL, 104 4 (2013) 44002DOI: https://doi.org/10.1209/0295-5075/104/44002