A novel wavelength modulation spectroscopy in TDLAS

•By superimposing the triple frequency modulation current on the fundamental frequency current, we present a novel wavelength modulation spectroscopy (WMS).•After selecting theoretical optimum modulation index, amplitude of the detected 2f improves 66% than that of the traditional wavelength modulation spectroscopy.•Minimum detection limit obtained by the new modulation method develops 56.5% in open-path background. We propose a novel wavelength modulation spectroscopy (WMS), which adds a triple frequency modulation current to the fundamental sinusoidal modulation current. By selecting theoretical optimum modulation indices, amplitude of the detected 2f improves 66% than that of the traditional wavelength modulation spectroscopy. Experimental results accord with theoretical expectation. Minimum detection limit obtained by the new modulation method develops 56.6% in open-path background. The transitions of CH4 at = 1.654 μm are selected to verify this method. Our method presents good application prospects and can be applied to sense of other gas molecules.