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• 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 multi-parameter fitting process. 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. [ABSTRACT FROM AUTHOR]

• A multi-laser hybrid sensor is designed based on tunable diode laser absorption spectroscopy (TDLAS) for simultaneous measurement of NH 3 , NO, and flue gas temperature. • In calibration-free wavelength modulation spectroscopy (CF-WMS) measurements, we used a method to obtain the laser wavelength response by a simple fit to the S 2f/1f line pattern of a standard gas with a standard deviation of less than 5 × 10-3 cm-1. • Under static conditions, the relative accuracy of NH 3 and NO detected by the sensor is 4.2% and 2%, respectively, and the maximum relative standard deviation of temperature is 1.3%. • When tested under flowing conditions, the sensor can accurately capture NH 3 , NO, and temperature changes. The relative accuracy of NH 3 and NO is 4.7% and 2.2%, and the relative standard deviation of temperature is 0.9%. The real-time monitoring of NH 3 , NO, and flue gas temperatures is critical to controlling NO x emissions from coal-fired power plants, reducing ammonia slip, and realizing accurate ammonia injection. However, few previous studies have utilized laser absorption sensors to measure these three indicators simultaneously. In this paper, a multi-laser hybrid sensor is designed based on tunable diode laser absorption spectroscopy (TDLAS) for simultaneous measurement of NH 3 , NO, and flue gas temperature. The sensor uses a distributed feedback (DFB) laser to target the NH 3 and the H 2 O lines, and a quantum cascade laser (QCL) is used to target the NO line. In the measurements of NH 3 and NO using calibration-free wavelength-modulated spectroscopy (CF-WMS), we employ a method to obtain the laser wavelength response by fitting the demodulated signal of a standard gas. Additionally, temperature measurements are obtained using the time-division multiplexing (TDM) strategy and direct absorption spectroscopy (DAS) techniques with the help of the absorption spectrum of H 2 O. Under static conditions, the relative accuracy of NH 3 and NO detected by the sensor is 4.2% and 2%, respectively, and the maximum relative standard deviation of temperature is 1.3%. When tested under flowing conditions, the sensor can accurately capture NH 3 , NO, and temperature changes. The relative accuracy of NH 3 and NO is 4.7% and 2.2%, and the relative standard deviation of temperature is 0.9%. The sensor has great potential in optimizing denitrification processes in thermal power plants. [ABSTRACT FROM AUTHOR]

Abstract: The spectral response of PHT-0044 (blue) and BCF-20 (green) scintillating fibers was measured as a function of wavelength using a UV LED. It was observed that significant spectral strength from the PHT-0044 fibers was missing compared to manufacturer''s specifications at the origin of the source, shifting the peak value of the spectrum to significantly higher values in wavelength. In contrast, the corresponding shift for the BCF-20 fibers was minimal. The mechanisms responsible for the observed behavior are discussed herein. Moreover, the attenuation length for each fiber type was extracted and studied as a function of wavelength. Finally, the measured fiber spectra were convolved with the wavelength response from a typical bi-alkali photomultiplier as well as a green-sensitive silicon photomultiplier and compared. [Copyright &y& Elsevier]