Tunable Diode-Laser Spectroscopy With Wavelength Modulation: A Calibration-Free Approach to the Recovery of Absolute Gas Absorption Line Shapes

Duffin, Kevin L.; McGettrick, Andrew; Johnstone, Walter; Stewart, George; Moodie, D.G.

doi:10.1109/jlt.2007.904937

Cited by 126 publications

(59 citation statements)

References 37 publications

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“…This can be applied to suppress any small residual RAM of the MG-Y diode laser, eliminate stable fringes, but also to amplitude modulate (AM) the diode laser. Work has been carried out to distinguishing the AM WMS signal from the FM induced WMS signal to study the absorption lineshape [25]. Furthermore, the SOA can also be used for studies of the effect of RAM on various optical components.…”

Section: Discussionmentioning

confidence: 99%

Fast and sensitive time-multiplexed gas sensing of multiple lines using a miniature telecom diode laser between 1529 nm and 1565 nm

et al. 2011

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High-sensitive multi-species detection around 1550 nm using a modulated grating Y-branch, MG-Y, diode laser tunable between 1529 nm and 1565 nm is presented. The MG-Y diode laser is based on the Vernier effect of two modulated gratings, and exhibits quasi-continuous tuning over 36 nm. Multi-species detection is achieved by fast sequential scanning of single absorption lines of CH 4 , CO, C 2 H 2 , and CO 2 distributed over the tuning range of the diode laser. The laser wavelength is scanned about 10 GHz around each absorption line for 5 ms and this is followed by a discrete large jump in operating wavelength to the next line.The MG-Y diode laser has a good repeatability in output frequency between sequential scan segments (<10 MHz) enabling averaging of the scans. The setup employs digital wavelength modulation spectroscopy, dWMS, with Fourier-

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Section: Discussionmentioning

confidence: 99%

Fast and sensitive time-multiplexed gas sensing of multiple lines using a miniature telecom diode laser between 1529 nm and 1565 nm

et al. 2011

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“…In this method, termed Wavelength Modulation Spectroscopy (WMS), the wavelength is modulated around a center λ o such that the harmonic amplitudes H n describe the signal [24] …”

Section: Research Backgroundmentioning

confidence: 99%

“…Prominent amongst these is the laser alignment onto the surface of the detector, since external vibrations present a significant problem with small surface-area detectors. Furthermore, although WMS effectively produces a frequency-modulated output, the residual amplitude modulation (RAM) cannot be neglected [24]. In the photoacoustic (PA) method, a strong coherent (laser) source is used to periodically heat a sample; provided the laser emission wavelength matches an absorption band of the gas species, the resulting pressure wave yields an indirect measure of the relative gas concentration [28], [29].…”

Section: Research Backgroundmentioning

confidence: 99%

A Robust Method for Tuning Photoacoustic Gas Detectors

Leis

Buttsworth

2018

IEEE Trans. Ind. Electron.

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Abstract-Detection of gases in industrial contexts is of great importance for ensuring safety in storage and transport, so as to limit atmospheric pollution and precisely control industrial and agricultural processes. Although chemical sensors are in widespread use, solidstate infrared detectors for gas sensing promise numerous advantages over conventional catalytic detectors in terms of sensitivity, calibration requirements, and lifetime. The laser-modulation photoacoustic approach is an alternative. Compared to other approaches, it provides more precise measurements with a stable zero baseline, as well as having significantly less complicated optics than cavity ringdown approaches. One enduring problem, though, is the relatively long time required to make photoacoustic measurements. The key contribution of this paper to the industrial context is twofold: first, we show how a sensitive dual-buffer acoustic resonator may be fabricated using 3D printing, and secondly we describe a method for localizing the peak absorption more rapidly than stepping a laser through the gas absorption profile. Modelling of the proposed approach demonstrates its potential, and the expected results are confirmed using an extensive experimental setup for the detection of methane in air.Index Terms-gas leak detection, infrared detectors, natural gas industry

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“…In other words, dTDLAS systems like HAI are usually not as sensitive to misalignments, dirt, or optical interfering structures as WMS systems but require higher absorbance (higher line strength or longer path length) to allow an implementation of our calibration-free approach. It is important to mention that for typical diode laser instruments (direct as well as WMS) a change of gas temperature, pressure, and concentration over a large range can cause large systematic offsets, which frequently require at least a three dimensional calibration procedure (including pressure, temperature, and concentration dependence) or the integration of complex assumptions (Duffin et al, 2007;Goldenstein et al, 2014;Rieker et al, 2009) to correct the data via a simulation model. WMS closed-path systems usually avoid this problem by always keeping gas temperature and pressure as close and constant as possible to the calibrated level, which is obviously not a viable approach for an open-path system.…”

Section: Signal Assessmentmentioning

confidence: 99%

HAI, a new airborne, absolute, twin dual-channel, multi-phase TDLAS-hygrometer: background, design, setup, and first flight data

et al. 2017

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Abstract. The novel Hygrometer for Atmospheric Investigation (HAI) realizes a unique concept for simultaneous gas-phase and total (gas-phase + evaporated cloud particles) water measurements. It has been developed and successfully deployed for the first time on the German HALO research aircraft. This new instrument combines direct tunable diode laser absorption spectroscopy (dTDLAS) with a firstprinciple evaluation method to allow absolute water vapor measurements without any initial or repetitive sensor calibration using a reference gas or a reference humidity generator. HAI contains two completely independent dual-channel (closed-path, open-path) spectrometers, one at 1.4 and one at 2.6 µm, which together allow us to cover the entire atmospheric H 2 O range from 1 to 40 000 ppmv with a single instrument. Both spectrometers each comprise a separate, wavelength-individual extractive, closed-path cell for total water (ice and gas-phase) measurements. Additionally, both spectrometers couple light into a common open-path cell outside of the aircraft fuselage for a direct, sampling-free, and contactless determination of the gas-phase water content. This novel twin dual-channel setup allows for the first time multiple self-validation functions, in particular a reliable, direct, in-flight validation of the open-path channels. During the first field campaigns, the in-flight deviations between the independent and calibration-free channels (i.e., closed-path to closed-path and open-path to closed-path) were on average in the 2 % range. Further, the fully autonomous HAI hygrometer allows measurements up to 240 Hz with a minimal integration time of 1.4 ms. The best precision is achieved by the 1.4 µm closed-path cell at 3.8 Hz (0.18 ppmv) and by the 2.6 µm closed-path cell at 13 Hz (0.055 ppmv). The requirements, design, operation principle, and first in-flight performance of the hygrometer are described and discussed in this work.

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Tunable Diode-Laser Spectroscopy With Wavelength Modulation: A Calibration-Free Approach to the Recovery of Absolute Gas Absorption Line Shapes

Cited by 126 publications

References 37 publications

Fast and sensitive time-multiplexed gas sensing of multiple lines using a miniature telecom diode laser between 1529 nm and 1565 nm

Fast and sensitive time-multiplexed gas sensing of multiple lines using a miniature telecom diode laser between 1529 nm and 1565 nm

A Robust Method for Tuning Photoacoustic Gas Detectors

HAI, a new airborne, absolute, twin dual-channel, multi-phase TDLAS-hygrometer: background, design, setup, and first flight data

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