Recovery of absolute gas absorption line shapes using tunable diode laser spectroscopy with wavelength modulation - Part 2: experimental investigation

James Roderic Peter Bain, Walter Johnstone, Keith Crawford Ruxton, George Stewart, Michael Lengden, Kevin Duffin

Research output: Contribution to journalArticle

36 Citations (Scopus)

Abstract

Recovery of absolute gas absorption line-shapes from 1st harmonic residual amplitude modulation (RAM) signals in tuneable diode laser spectroscopy with wavelength modulation (TDLS-WM) offers significant advantages in terms of measurement accuracy (for gas concentration and pressure), freedom from the need for calibration and resilience to errors or drift in system parameters / scaling factors. However, the signal strength and signal to noise ratio are compromised somewhat relative to conventional wavelength modulation spectroscopy (WMS) by the signal dependency on the laser’s intensity modulation amplitude rather than on the direct intensity, and by the need to operate at low modulation index, m (<0.75), in the previously reported work. In Part 1 of this two part publication, we report a more universal approach to the analysis of recovered RAM signals and absolute absorption line-shapes. This new approach extends the use of RAM techniques to arbitrary m values up to 2.2. In addition, it provides the basis for a comparison of signal strength between the RAM signals recovered by the phasor decomposition approach and conventional 1st and 2nd harmonic TDLS-WM signals. The experimental work reported here validates the new model and demonstrates the use of the RAM techniques for accurate recovery of absolute gas absorption line-shapes to m = 2.2 and above. Furthermore, it demonstrates that the RAM signal strengths can be increased significantly by increasing the modulation frequency and defines regimes of operation such that the directly recovered RAM signals are comparable to or even greater than the widely used, conventional 2nd harmonic TDLS-WM signal. Finally, a critique of the RAM techniques relative to the conventional approaches is given.
LanguageEnglish
Pages987-996
Number of pages10
JournalJournal of Lightwave Technology
Volume29
Issue number7
Early online date20 Jan 2011
DOIs
Publication statusPublished - 1 Apr 2011

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laser spectroscopy
line shape
recovery
diodes
modulation
gases
wavelengths
harmonics
resilience
frequency modulation
signal to noise ratios
decomposition
scaling

Keywords

  • absorption line-shape recovery, diode laser spectroscopy, gas sensors, industrial and environmental monitoring, wavelength modulation spectroscopy
  • frequency modulation
  • random access
  • harmonic analysis
  • resonant frequency

Cite this

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title = "Recovery of absolute gas absorption line shapes using tunable diode laser spectroscopy with wavelength modulation - Part 2: experimental investigation",
abstract = "Recovery of absolute gas absorption line-shapes from 1st harmonic residual amplitude modulation (RAM) signals in tuneable diode laser spectroscopy with wavelength modulation (TDLS-WM) offers significant advantages in terms of measurement accuracy (for gas concentration and pressure), freedom from the need for calibration and resilience to errors or drift in system parameters / scaling factors. However, the signal strength and signal to noise ratio are compromised somewhat relative to conventional wavelength modulation spectroscopy (WMS) by the signal dependency on the laser’s intensity modulation amplitude rather than on the direct intensity, and by the need to operate at low modulation index, m (<0.75), in the previously reported work. In Part 1 of this two part publication, we report a more universal approach to the analysis of recovered RAM signals and absolute absorption line-shapes. This new approach extends the use of RAM techniques to arbitrary m values up to 2.2. In addition, it provides the basis for a comparison of signal strength between the RAM signals recovered by the phasor decomposition approach and conventional 1st and 2nd harmonic TDLS-WM signals. The experimental work reported here validates the new model and demonstrates the use of the RAM techniques for accurate recovery of absolute gas absorption line-shapes to m = 2.2 and above. Furthermore, it demonstrates that the RAM signal strengths can be increased significantly by increasing the modulation frequency and defines regimes of operation such that the directly recovered RAM signals are comparable to or even greater than the widely used, conventional 2nd harmonic TDLS-WM signal. Finally, a critique of the RAM techniques relative to the conventional approaches is given.",
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Recovery of absolute gas absorption line shapes using tunable diode laser spectroscopy with wavelength modulation - Part 2 : experimental investigation. / Bain, James Roderic Peter; Johnstone, Walter; Ruxton, Keith Crawford; Stewart, George; Lengden, Michael; Duffin, Kevin.

In: Journal of Lightwave Technology, Vol. 29, No. 7, 01.04.2011, p. 987-996.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Recovery of absolute gas absorption line shapes using tunable diode laser spectroscopy with wavelength modulation - Part 2

T2 - Journal of Lightwave Technology

AU - Bain, James Roderic Peter

AU - Johnstone, Walter

AU - Ruxton, Keith Crawford

AU - Stewart, George

AU - Lengden, Michael

AU - Duffin, Kevin

PY - 2011/4/1

Y1 - 2011/4/1

N2 - Recovery of absolute gas absorption line-shapes from 1st harmonic residual amplitude modulation (RAM) signals in tuneable diode laser spectroscopy with wavelength modulation (TDLS-WM) offers significant advantages in terms of measurement accuracy (for gas concentration and pressure), freedom from the need for calibration and resilience to errors or drift in system parameters / scaling factors. However, the signal strength and signal to noise ratio are compromised somewhat relative to conventional wavelength modulation spectroscopy (WMS) by the signal dependency on the laser’s intensity modulation amplitude rather than on the direct intensity, and by the need to operate at low modulation index, m (<0.75), in the previously reported work. In Part 1 of this two part publication, we report a more universal approach to the analysis of recovered RAM signals and absolute absorption line-shapes. This new approach extends the use of RAM techniques to arbitrary m values up to 2.2. In addition, it provides the basis for a comparison of signal strength between the RAM signals recovered by the phasor decomposition approach and conventional 1st and 2nd harmonic TDLS-WM signals. The experimental work reported here validates the new model and demonstrates the use of the RAM techniques for accurate recovery of absolute gas absorption line-shapes to m = 2.2 and above. Furthermore, it demonstrates that the RAM signal strengths can be increased significantly by increasing the modulation frequency and defines regimes of operation such that the directly recovered RAM signals are comparable to or even greater than the widely used, conventional 2nd harmonic TDLS-WM signal. Finally, a critique of the RAM techniques relative to the conventional approaches is given.

AB - Recovery of absolute gas absorption line-shapes from 1st harmonic residual amplitude modulation (RAM) signals in tuneable diode laser spectroscopy with wavelength modulation (TDLS-WM) offers significant advantages in terms of measurement accuracy (for gas concentration and pressure), freedom from the need for calibration and resilience to errors or drift in system parameters / scaling factors. However, the signal strength and signal to noise ratio are compromised somewhat relative to conventional wavelength modulation spectroscopy (WMS) by the signal dependency on the laser’s intensity modulation amplitude rather than on the direct intensity, and by the need to operate at low modulation index, m (<0.75), in the previously reported work. In Part 1 of this two part publication, we report a more universal approach to the analysis of recovered RAM signals and absolute absorption line-shapes. This new approach extends the use of RAM techniques to arbitrary m values up to 2.2. In addition, it provides the basis for a comparison of signal strength between the RAM signals recovered by the phasor decomposition approach and conventional 1st and 2nd harmonic TDLS-WM signals. The experimental work reported here validates the new model and demonstrates the use of the RAM techniques for accurate recovery of absolute gas absorption line-shapes to m = 2.2 and above. Furthermore, it demonstrates that the RAM signal strengths can be increased significantly by increasing the modulation frequency and defines regimes of operation such that the directly recovered RAM signals are comparable to or even greater than the widely used, conventional 2nd harmonic TDLS-WM signal. Finally, a critique of the RAM techniques relative to the conventional approaches is given.

KW - absorption line-shape recovery, diode laser spectroscopy, gas sensors, industrial and environmental monitoring, wavelength modulation spectroscopy

KW - frequency modulation

KW - random access

KW - harmonic analysis

KW - resonant frequency

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DO - 10.1109/JLT.2011.2107729

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JO - Journal of Lightwave Technology

JF - Journal of Lightwave Technology

SN - 0733-8724

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ER -