Fig. 1. Composition of DFG laser system

Fig. 2. Experimental system of hydrocarbon gas detection

Fig. 3. Absorption spectra of small hydrocarbon molecules and benzene in the range of 3250‒3400 nm. (a) Absorption spectra of methane; (b) absorption spectra of ethane; (c) absorption spectra of ethylene; (d) absorption spectra of propane; (e) absorption spectra of propylene; (f) absorption spectra of butane; (g) absorption spectra of benzene; (h) comparison between 298 K methane experiment and HITRAN database

Fig. 4. Parts of hydrocarbon absorption peaks changed with temperature. (a) Absorption peaks of methane at 3270 nm; (b) absorption peaks of propane at 3369 nm; (c) absorption peaks of benzene at 3270 nm

Fig. 5. Parts of hydrocarbon absorption peaks changed with volume fraction. (a) Absorption peaks of methane; (b) absorption peaks of ethane

Fig. 6. Gas absorption signals from the heating decomposition of coal