he theory of wavelength modulation PAS has been described in detail by several authors [11] and [12]. The sensor was operated according to the optimum design conditions. Wavelength modulated light from the TEDFL is scanned by loading a combined ramp voltage and sinusoidal waveform voltage. The simultaneously and continuously measured results of gas mixtures with H2O, C2H2, CO and CO2 are shown in Fig. 3.