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The expressions of the second harmonic(2f) signal are derived on the basis of absorption spectral and lock-in theories.A parametric study indicates that the phase shift between the intensity and wavelength modulation makes a great contribution to the 2f signal.A self-calibration wavelength modulation spectroscopy(WMS) method based on tunable diode laser absorption spectroscopy(TOLAS) is applied,combining the advantages of ambient pressure,temperature suppression,and phase-shift influences elimination.Species concentration is retrieved simultaneously from selected 2f signal pairs of measured and reference WMS-2f spectra.The absorption line of acetylene(C_2H_2) at 1530.36 nm near-infrared is selected to detect C_2H_2 concentrations in the range of 0-400 ppmv.System sensitivity,detection precision and limit are markedly improved,demonstrating that the self-calibration method has better detecting performance than the conventional WMS.
The expressions of the second harmonic (2f) signal are derived on the basis of absorption spectral and lock-in theories. A parametric study that that phase shift between the intensity and wavelength modulation makes a great contribution to the 2f signal. A self- calibration wavelength modulation spectroscopy (WMS) method based on tunable diode laser absorption spectroscopy (TOLAS) is applied, combining the advantages of ambient pressure, temperature suppression, and phase-shift influences elimination. Species concentration is retrieved simultaneously from selected 2f signal pairs of measured and reference WMS-2f spectra. The absorption line of acetylene (C_2H_2) at 1530.36 nm near-infrared is selected to detect C_2H_2 concentrations in the range of 0-400 ppmv. System sensitivity, detection precision and limit are markedly improved, demonstrating that the self-calibration method has better detection performance than the conventional WMS.