Rapid, Time-Division Multiplexed, Direct Absorption- and Wavelength Modulation-Spectroscopy

被引:66
作者
Klein, Alexander [1 ]
Witzel, Oliver [1 ]
Ebert, Volker [1 ,2 ]
机构
[1] Phys Tech Bundesanstalt, D-38116 Braunschweig, Germany
[2] Tech Univ Darmstadt, Ctr Smart Interfaces, D-64287 Darmstadt, Germany
关键词
trace gas measurement; absorption spectroscopy; TDLAS; WMS; hygrometer; calibration-free; DIODE-LASER SPECTROSCOPY; WATER-VAPOR; TEMPERATURE; PRESSURE; COMPACT; SENSOR; CO;
D O I
10.3390/s141121497
中图分类号
O65 [分析化学];
学科分类号
070302 ; 081704 ;
摘要
We present a tunable diode laser spectrometer with a novel, rapid time multiplexed direct absorption-and wavelength modulation-spectroscopy operation mode. The new technique allows enhancing the precision and dynamic range of a tunable diode laser absorption spectrometer without sacrificing accuracy. The spectroscopic technique combines the benefits of absolute concentration measurements using calibration-free direct tunable diode laser absorption spectroscopy (dTDLAS) with the enhanced noise rejection of wavelength modulation spectroscopy (WMS). In this work we demonstrate for the first time a 125 Hz time division multiplexed (TDM-dTDLAS-WMS) spectroscopic scheme by alternating the modulation of a DFB-laser between a triangle-ramp (dTDLAS) and an additional 20 kHz sinusoidal modulation (WMS). The absolute concentration measurement via the dTDLAS-technique allows one to simultaneously calibrate the normalized 2f/1f-signal of the WMS-technique. A dTDLAS/WMS-spectrometer at 1.37 mu m for H2O detection was built for experimental validation of the multiplexing scheme over a concentration range from 50 to 3000 ppmV (0.1 MPa, 293 K). A precision of 190 ppbV was achieved with an absorption length of 12.7 cm and an averaging time of two seconds. Our results show a five-fold improvement in precision over the entire concentration range and a significantly decreased averaging time of the spectrometer.
引用
收藏
页码:21497 / 21513
页数:17
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