Fig. 1. (a) Schematic of concentration detecting device of C2H2; (b) photo of compact C2H2 detecting instrument

Fig. 2. Diagram of whole driving circuit

Fig. 3. Variation of peak wavenumber of laser with injection current at different temperatures

Fig. 4. Second harmonic signal amplitude of standard gas with C2H2 volume fraction of 5×10-5 at different total pressures and modulation amplitudes

Fig. 5. (a) Wavelength modulation second harmonic signals for C2H2 with different volume fractions; (b) relationship between amplitude of second harmonic signal and C2H2 volume fraction; (c) detecting deviation

Fig. 6. (a) Experimental detecting data for 60 s; (b) Allan variance of detecting system