A novel methodology for characterizing DFB laser wavelength response (WR) in wavelength modulation spectroscopy (WMS)

A novel methodology to directly characterize the wavelength response (WR) of a DFB laser in wavelength modulation spectroscopy (WMS) is proposed. This method circumvents the cumbersome etalon signal peak counting process which brings in manual errors easily. The particle swarm optimization (PSO) algorithm was employed to effectively address the challenges encountered during the fitting process, which involved as many as 7 parameters in the WR. The WR with different combinations of frequencies of scan and modulation, as well as modulation amplitudes were characterized by this method. And it is shown that there exist negligible differences when comparing the results with those by traditional etalon peaking counting method. In order to verify the accuracy of this method, two tunable diode lasers emitting near 7185.59 cm⁻¹ and 7444.35 cm⁻¹ were employed to perform the measurements of temperature above a burner with calibration-free WMS-2f/1f and direct absorption spectroscopy (DAS), respectively. The temperature measured by two techniques shows great accordance, which indicates the accuracy of WR deduced by the proposed method.