Behaviors of harmonic signals in wavelength modulation spectroscopy （WMS） for gas detection with Lorentzian line under high absorption strength are investigated. Approximate analytic expressions of the second, fourt...Behaviors of harmonic signals in wavelength modulation spectroscopy （WMS） for gas detection with Lorentzian line under high absorption strength are investigated. Approximate analytic expressions of the second, fourth, and sixth harmonics on the strength ave presented in concise forms. Simulations show that the expressions ave in agreement with the Fourier expansion by numerical integration. It is expected theoretically and experimentally in a WMS system for methane detection that there ave not only a maximum, but also a null point in the harmonics versus strength relations, which should be of practical importance in methane sensing applications.展开更多
文摘Behaviors of harmonic signals in wavelength modulation spectroscopy （WMS） for gas detection with Lorentzian line under high absorption strength are investigated. Approximate analytic expressions of the second, fourth, and sixth harmonics on the strength ave presented in concise forms. Simulations show that the expressions ave in agreement with the Fourier expansion by numerical integration. It is expected theoretically and experimentally in a WMS system for methane detection that there ave not only a maximum, but also a null point in the harmonics versus strength relations, which should be of practical importance in methane sensing applications.
