A calibration-free methodology for resonantly enhanced photoacoustic spectroscopy using quantum cascade lasers

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Abstract

Photoacoustic spectroscopy (PAS) is a highly sensitive technique for trace gas sensing, which requires frequent re-calibration for changing environmental influences and input light power fluctuation. This is a major drawback against its deployment for on-site, long-term remote applications. To address this drawback here we present the theory and application of a Calibration-Free Wavelength Modulation Photoacoustic Spectroscopy (CF-WM-PAS) technique. It is applied for measurements of CH4 gas concentration in the mid-infrared at 8.6 μm wavelength using a Quantum Cascade Laser (QCL). The method normalizes the second harmonic (R2f) component, dominated by laser-gas interaction and optical intensity, by the first harmonic (R1f) component dominated by Residual Amplitude Modulation (RAM) DC offset, to isolate the output from changes in the gas matrix, optical intensity and electrical gain. This normalization technique removes influences from changes in the resonant frequency, gas concentration and incident optical power. It is confirmed using a ±1600 Hz change in modulation frequency around the resonance, a 1% to 10% change in gas concentration and an up to 78.3% attenuation in input light intensity with a custom built miniaturized 3D-printed sensor. A Normalized Noise Equivalent Absorption (NNEA) of 4.85×10 -9 Wcm -1Hz -1/2 for calibration-free R2f/R1f measurements is demonstrated.
Original languageEnglish
Pages (from-to)1-9
Number of pages9
JournalIEEE Sensors Journal
Early online date7 Jan 2020
DOIs
Publication statusE-pub ahead of print - 7 Jan 2020

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Photoacoustic spectroscopy
Quantum cascade lasers
photoacoustic spectroscopy
quantum cascade lasers
Calibration
methodology
Gases
gases
harmonics
Gas lasers
Wavelength
Amplitude modulation
gas lasers
Frequency modulation
wavelengths
frequency modulation
luminous intensity
resonant frequencies
Natural frequencies
attenuation

Keywords

  • photoacoustic spectroscopy
  • 3D printing
  • quantum cascade lasers
  • calibration free
  • miniaturized
  • gas sensing

Cite this

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title = "A calibration-free methodology for resonantly enhanced photoacoustic spectroscopy using quantum cascade lasers",
abstract = "Photoacoustic spectroscopy (PAS) is a highly sensitive technique for trace gas sensing, which requires frequent re-calibration for changing environmental influences and input light power fluctuation. This is a major drawback against its deployment for on-site, long-term remote applications. To address this drawback here we present the theory and application of a Calibration-Free Wavelength Modulation Photoacoustic Spectroscopy (CF-WM-PAS) technique. It is applied for measurements of CH4 gas concentration in the mid-infrared at 8.6 μm wavelength using a Quantum Cascade Laser (QCL). The method normalizes the second harmonic (R2f) component, dominated by laser-gas interaction and optical intensity, by the first harmonic (R1f) component dominated by Residual Amplitude Modulation (RAM) DC offset, to isolate the output from changes in the gas matrix, optical intensity and electrical gain. This normalization technique removes influences from changes in the resonant frequency, gas concentration and incident optical power. It is confirmed using a ±1600 Hz change in modulation frequency around the resonance, a 1{\%} to 10{\%} change in gas concentration and an up to 78.3{\%} attenuation in input light intensity with a custom built miniaturized 3D-printed sensor. A Normalized Noise Equivalent Absorption (NNEA) of 4.85×10 -9 Wcm -1Hz -1/2 for calibration-free R2f/R1f measurements is demonstrated.",
keywords = "photoacoustic spectroscopy, 3D printing, quantum cascade lasers, calibration free, miniaturized, gas sensing",
author = "Metin Ilke and Ralf Bauer and Michael Lengden",
note = "{\circledC} 2020 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.",
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N2 - Photoacoustic spectroscopy (PAS) is a highly sensitive technique for trace gas sensing, which requires frequent re-calibration for changing environmental influences and input light power fluctuation. This is a major drawback against its deployment for on-site, long-term remote applications. To address this drawback here we present the theory and application of a Calibration-Free Wavelength Modulation Photoacoustic Spectroscopy (CF-WM-PAS) technique. It is applied for measurements of CH4 gas concentration in the mid-infrared at 8.6 μm wavelength using a Quantum Cascade Laser (QCL). The method normalizes the second harmonic (R2f) component, dominated by laser-gas interaction and optical intensity, by the first harmonic (R1f) component dominated by Residual Amplitude Modulation (RAM) DC offset, to isolate the output from changes in the gas matrix, optical intensity and electrical gain. This normalization technique removes influences from changes in the resonant frequency, gas concentration and incident optical power. It is confirmed using a ±1600 Hz change in modulation frequency around the resonance, a 1% to 10% change in gas concentration and an up to 78.3% attenuation in input light intensity with a custom built miniaturized 3D-printed sensor. A Normalized Noise Equivalent Absorption (NNEA) of 4.85×10 -9 Wcm -1Hz -1/2 for calibration-free R2f/R1f measurements is demonstrated.

AB - Photoacoustic spectroscopy (PAS) is a highly sensitive technique for trace gas sensing, which requires frequent re-calibration for changing environmental influences and input light power fluctuation. This is a major drawback against its deployment for on-site, long-term remote applications. To address this drawback here we present the theory and application of a Calibration-Free Wavelength Modulation Photoacoustic Spectroscopy (CF-WM-PAS) technique. It is applied for measurements of CH4 gas concentration in the mid-infrared at 8.6 μm wavelength using a Quantum Cascade Laser (QCL). The method normalizes the second harmonic (R2f) component, dominated by laser-gas interaction and optical intensity, by the first harmonic (R1f) component dominated by Residual Amplitude Modulation (RAM) DC offset, to isolate the output from changes in the gas matrix, optical intensity and electrical gain. This normalization technique removes influences from changes in the resonant frequency, gas concentration and incident optical power. It is confirmed using a ±1600 Hz change in modulation frequency around the resonance, a 1% to 10% change in gas concentration and an up to 78.3% attenuation in input light intensity with a custom built miniaturized 3D-printed sensor. A Normalized Noise Equivalent Absorption (NNEA) of 4.85×10 -9 Wcm -1Hz -1/2 for calibration-free R2f/R1f measurements is demonstrated.

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