Photoacoustic multicomponent gas analysis using a Levenberg-Marquardt fitting algorithm

Moeckli, M.; Hilbes, Christian; Sigrist, Markus W.

doi:10.1007/s003400050529

Cited by 38 publications

(18 citation statements)

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“…These figures show that the amplitude of the PA signal increases with the buffer radius and that the highest absolute sensitivity is obtained for the largest radius (60 mm) except for the 0.97-1.07 m −1 absorption coefficient range. At low absorption levels (below 0.05 m −1 ) and without kinetic cooling effect [24,[38][39][40], the PA signal is proportional to the absorption of the compound present in the cell [1]. At higher absorption levels, the PA signal is no longer proportional to the absorption coefficient but shows a maximum (Fig.…”

Section: Resultsmentioning

confidence: 94%

Investigation and optimisation of a multipass resonant photoacoustic cell at high absorption levels

et al. 2005

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A theoretical and experimental investigation of photoacoustic (PA) signals in a resonant multipass PA cell with high background absorption (up to 29 m −1 ) is presented. An analogous electric transmission line model including discontinuity inductances at cross section changes was used to model the first longitudinal acoustic mode of the multipass PA cell equipped with two buffer volumes. This model was validated with experimentally obtained results and used to predict the behaviour of the PA cell for different multipass arrangements and different buffer volume diameters. The highest PA signal is obtained for high pass number and large buffer radius. Increasing the absorption coefficient of the medium enhances the PA signal until a maximum is reached, leading to a minimum for the PA signal sensitivity. For a given background absorption, the number of passes required to maximise the sensitivity depends on the absorption coefficient. The model allows the determination of the best-suited number of passes for a given absorption coefficient and cell geometry.PACS 82.80.Kd; 42.62.Fi; 82.80.Gk IntroductionPhotoacoustic (PA) spectroscopy is a powerful technique for detecting traces of gases due to its intrinsically high sensitivity, large dynamic range, and comparatively simple experimental set-up [1-3]. The detection limit of this technique is mainly determined by the light source used and the PA cell design. The sensitivity of PA cells has been improved by acoustic amplification of the PA signal thanks to the use of resonant PA cells [4][5][6][7][8][9][10][11]. Resonant cells have also been designed for multipass or intracavity operation [12][13][14][15][16]. Cell windows generate synchronous noise which has been minimized by introducing acoustic baffles [17], by the development of a "windowless" [18] or differential cell [19,20].Owing to its high sensitivity, PA spectroscopy is usually applied to the detection of weak absorption signals. In the case of low optical absorption, a uniform heat deposition along the light beam is observed and the generated PA signal depends only on the quantity of absorbed power. Nevertheless, even u Fax: +41-1-633-1230, E-mail: sigrist@iqe.phys.ethz.ch if the low absorption case is frequent, strong background absorption is sometimes present. This is particularly the case for in-situ monitoring where carbon dioxide, ammonia, alcohol or water absorptions can interfere with the species under investigation. At high absorption, the incident light power decreases exponentially in the PA cell and the course of the absorption along the beam path has to be taken into account for modelling the PA signal. Due to the longer absorption path in multipass cells, the exponential radiation decay affects the PA response more strongly than the one of single-pass cells. High-absorption phenomena have been observed previously in pulsed PA spectroscopy [21,22]. These effects are important since they influence both the PA response in presence of a highly absorbing background and the dynamic range of a ...

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Section: Resultsmentioning

confidence: 94%

Investigation and optimisation of a multipass resonant photoacoustic cell at high absorption levels

et al. 2005

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“…The amplitude of the L-PAS signal increases with the water content and levels off at Ͼ0.5% absolute humidity level, with signal approximately three times that in dry air. The phase of NO 2 signal also changes from dry air to 1% absolute humidity, a clear indication of relaxation effects (9). Therefore, a QCL-PAS-based ambient NO 2 sensor will require a simultaneous humidity measurement, most conveniently ac- complished by measuring a nearby strong water absorption line in the same spectral trace (Fig.…”

Section: Resultsmentioning

confidence: 99%

Sub-parts-per-billion level detection of NO ₂ using room-temperature quantum cascade lasers

Pushkarsky

Tsekoun

Dunayevskiy

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

122

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We report the sub-parts-per-billion-level detection of NO2 using tunable laser-based photoacoustic spectroscopy where the laser radiation is obtained from a room-temperature continuous-wave high-power quantum cascade laser operating in an external grating cavity configuration. The continuously tunable external grating cavity quantum cascade laser produces maximum single-frequency output of Ϸ300 mW tunable over Ϸ350 nm centered at 6.25 m. We demonstrate minimum detection level of Ϸ0.5 parts per billion of NO2 in the presence of humidified air.IR lasers ͉ NO2 spectroscopy ͉ photoacoustic spectroscopy ͉ sub-parts-per-billion detection of gases R eal-time trace-level gas detection is an area of fast growth with applications in such diverse fields as medical diagnostics, process control, national security, and environmental airquality monitoring. Techniques based on the measurement of optical absorption using tunable laser sources are attractive detection methods because of their intrinsic sensitivity and selectivity, i.e., an ability for discriminating against interferents (1, 2). The most recent advances, intercomparison of spectroscopic techniques, and status of available laser sources are summarized in a recent review (3). Furthermore, photoacoustic (PA) spectroscopy is seen to be well suited for optical absorption measurements because it combines high sensitivity with the ruggedness needed for field-deployable instrumentation. However, laser PA spectroscopy (L-PAS) requires multihundredmilliwatt-level laser sources to achieve a sub-parts-per-billion (sub-ppb) level of sensitivity for many of the environmentally and industrially important gases. As a result, heretofore most of the sensitive L-PAS detection schemes have used continuouswave (CW) molecular gas lasers (4). Results and DiscussionHigh-Power Continuously Tunable Laser Source. The tuning characteristics of our high-power single-frequency source are seen in Fig. 1, which shows the single-mode laser power available from the CW room temperature (RT) external grating cavity (EGC) quantum cascade laser (QCL) (near 6.3 m) at several grating settings. Fig. 1 also shows the overall tuning of the output that covers Ͼ350 nm with CW RT laser power in excess of Ϸ200 mW with maximum CW RT laser power of 300 mW near the center of the tuning curve. Details are given in Materials and Methods.PA Spectroscopy of NO2. We have used the broadly and continuously tunable, high-power CW RT EGC-QCL source for PA spectroscopy of NO 2 , which exhibits strong absorption features near Ϸ1,600 cm Ϫ1 . NO 2 is a smog and particulate matter precursor and one of the key pollutants that is routinely monitored. Ambient concentrations of NO 2 typically are in single digits to tens of parts per billion (ppb) levels (5). The national ambient air quality standard (NAAQS) level for NO 2 is 53 ppb for arithmetic mean average (6). Consequently, an acceptable ambient NO 2 sensor should have single-digit ppb or, better, sub-ppb, sensitivity. Earlier, cryogenically cooled lead salt lasers (7) operat...

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“…Instead, considerable effort is needed to discriminate the various components, as well as to identify any unexpected component. Iterative algorithms using least squares regression and based on prior knowledge of the absorption cross sections (σ ij ) have been developed to fit the photoacoustic spectrum of multicomponent samples (Moeckli, 1998).…”

Section: Photoacoustic Effect In Gasesmentioning

confidence: 99%

Detection of Greenhouse Gases Using the Photoacoustic Spectroscopy

Sthel¹,

Gomes²,

Lima³

et al. 2012

Greenhouse Gases - Emission, Measurement and Management

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Photoacoustic multicomponent gas analysis using a Levenberg-Marquardt fitting algorithm

Cited by 38 publications

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Investigation and optimisation of a multipass resonant photoacoustic cell at high absorption levels

Investigation and optimisation of a multipass resonant photoacoustic cell at high absorption levels

Sub-parts-per-billion level detection of NO ₂ using room-temperature quantum cascade lasers

Detection of Greenhouse Gases Using the Photoacoustic Spectroscopy

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Photoacoustic multicomponent gas analysis using a Levenberg-Marquardt fitting algorithm

Cited by 38 publications

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Investigation and optimisation of a multipass resonant photoacoustic cell at high absorption levels

Investigation and optimisation of a multipass resonant photoacoustic cell at high absorption levels

Sub-parts-per-billion level detection of NO 2 using room-temperature quantum cascade lasers

Detection of Greenhouse Gases Using the Photoacoustic Spectroscopy

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Sub-parts-per-billion level detection of NO ₂ using room-temperature quantum cascade lasers