scholarly journals Highly Sensitive, Calibration-Free WM-DAS Method for Recovering Absorbance—Part I: Theoretical Analysis

Sensors ◽  
2020 ◽  
Vol 20 (3) ◽  
pp. 681 ◽  
Author(s):  
Zhimin Peng ◽  
Yanjun Du ◽  
Yanjun Ding
Keyword(s):  
Absorption Spectroscopy ◽  
High Sensitivity ◽  
Laser Frequency ◽  
High Accuracy ◽  
Tunable Diode Laser ◽  
Direct Absorption Spectroscopy ◽  
Noise Rejection ◽  
Preliminary Validation ◽  
Validation Experiment ◽  
Calibration Free

The absorbance is of great importance in the tunable diode laser absorption spectroscopy (TDLAS) as it contains information of both gas properties and spectroscopic parameters. A novel, calibration-free wavelength modulation-direct absorption spectroscopy (WM-DAS) is proposed and experimentally verified in this two-part paper. This method combines the capability of absorbance measurement from DAS and the advantages of enhanced noise rejection and high sensitivity from WMS. In this Part I, we focus on the full theoretical basis and procedures of this method from the following three aspects: the high-accuracy characterizations of laser frequency and intensity, noise rejection ability by extracting the characteristic spectra through the fast Fourier transform (FFT) of the light intensity, and the simultaneous fitting strategy for both baseline and absorbance. The preliminary validation experiment of CO transition at 4300.6999 cm−1 in a static gas cell shows the high accuracy of the proposed method.

scholarly journals High-accuracy sinewave-scanned direct absorption spectroscopy

2018 ◽  
Vol 26 (22) ◽  
pp. 29550 ◽  
Author(s):  
Yanjun Du ◽  
Zhimin Peng ◽  
Yanjun Ding
Keyword(s):  
Absorption Spectroscopy ◽  
High Accuracy ◽  
Direct Absorption ◽  
Direct Absorption Spectroscopy

scholarly journals A Wide-Range and Calibration-Free Spectrometer Which Combines Wavelength Modulation and Direct Absorption Spectroscopy with Cavity Ringdown Spectroscopy

Sensors ◽  
2020 ◽  
Vol 20 (3) ◽  
pp. 585 ◽  
Author(s):  
Zhen Wang ◽  
Yanjun Du ◽  
Yanjun Ding ◽  
Zhimin Peng
Keyword(s):  
Diode Laser ◽  
Tunable Diode Laser ◽  
Cavity Ringdown Spectroscopy ◽  
Wavelength Modulation ◽  
Direct Absorption ◽  
Cavity Ringdown ◽  
Direct Absorption Spectroscopy ◽  
Ringdown Time ◽  
Wide Range ◽  
Calibration Free

A wide-range, calibration-free tunable diode laser spectrometer is established by combining wavelength modulation and direct absorption spectroscopy (WM-DAS) with continuous wave cavity ringdown spectroscopy (CW-CRDS). This spectrometer combines the benefits of absolute concentration measurements, wide range, and high speed, using WM-DAS with enhanced noise reduction in CW-CRDS. The accurate baseline ringdown time, τ0, is calculated by the absorption peak (measured by WM-DAS) and the ringdown time containing gas absorption information (measured by CW-CRDS at the center wavelength of the spectral line). The gas concentration is obtained without measuring τ0 in real time, thus, greatly improving the measuring speed. A WM-DAS/CW-CRDS spectrometer at 1.57 μm for CO detection was assembled for experimental validation of the multiplexing scheme over a concentration ranging from 4 ppm to 1.09% (0.1 MPa, 298 K). The measured concentration of CO at 6374.406 cm−1 shows that the dynamic range of this tunable diode laser absorption spectrometer is extendable up to five orders of magnitude and the corresponding precision is improved. The measurement speed of this spectrometer can extend up to 10 ms, and the detection limit can reach 35 ppb within 25 s.

Generation of stable and tunable optical frequency linked to a radio frequency by use of a high finesse cavity and its application in absorption spectroscopy

2022 ◽  
Author(s):  
Yueting Zhou ◽  
Gang Zhao ◽  
Jianxin Liu ◽  
Xiaojuan Yan ◽  
Zhixin Li ◽  
...  
Keyword(s):  
Radio Frequency ◽  
Absorption Spectroscopy ◽  
Frequency Comb ◽  
External Cavity ◽  
Frequency Instability ◽  
Laser Frequency ◽  
Detection Sensitivity ◽  
Optical Frequency ◽  
Direct Absorption Spectroscopy ◽  
High Finesse

Abstract The laser frequency could be linked to an radio frequency through an external cavity by the combination of Pound-Drever-Hall and Devoe-Brewer locking techniques. A stable and tunable optical frequency at wavelength of 1.5 μm obtained by a cavity with high finesse of 96,000 and a fiber laser, calibrated by a commercial optical frequency comb, has been demonstrated. The locking performances have been analyzed by in-loop and out-loop noises, indicating that the absolute frequency instability could be down to 50 kHz over 1 s and keep to less than 110 kHz over 2.5 h. Then, the application of this stabilized laser to the direct absorption spectroscopy has been performed. With the help of balanced detection, the detection sensitivity, in terms of optical density, can reach to 9.4×10-6.

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