Abstract

Recovery of absolute gas absorption line shapes from first harmonic residual AM (RAM) signals in tunable 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 SNR are compromised somewhat relative to conventional WM spectroscopy (WMS) by the signal dependence 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 study. 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 first and second harmonic TDLS-WM signals. The experimental study 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 second harmonic TDLS-WM signal. Finally, a critique of the RAM techniques relative to the conventional approaches is given.

© 2011 IEEE

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  1. J. Reid, D. Labrie, "Second-harmonic detection with tunable diode lasers—Comparison of experiment and theory ," Appl. Phys. B, Lasers Opt. 26, 203-210 (1981).
  2. J. A. Silver, "Frequency-modulation spectroscopy for trace species detection: Theory and comparison among experimental methods," Appl. Opt. 31, 707-717 (1992).
  3. J. M. Supplee, E. A. Whittaker, W. Lenth, "Theoretical description of frequency modulation and wavelength modulation spectroscopy ," Appl. Opt. 33, 6294-6302 (1994).
  4. P. Werle, "A review of recent advances in semiconductor laser based gas monitors," Spectrochimica Acta A, Mol. Biomol. Spectrosc. 54, 197-236 (1998).
  5. G. Stewart, C. Tandy, D. Moodie, M. A. Morante, F. Dong, "Design of a fibre optic multipoint sensor for gas detection," Sens. Actuat. B, Chem. 51, 227-232 ( 1998).
  6. P. W. Werle, P. Mazzinghi, F. D'Amato, M. De Rosa, K. Maurer, F. Slemr, "Signal processing and calibration procedures for in situ diode laser absorption spectroscopy ," Spectrochimica Acta A 60, 1685-1705 (2004).
  7. D. Richter, D. G. Lancaster, F. K. Tittel, "Development of an automated diode laser based multicomponent gas sensor," Appl. Opt. 39, 4444-4450 (2000).
  8. L. C. Philippe, R. K. Hanson, "Laser diode wavelength—Modulation spectroscopy for simultaneous measurement of temperature, pressure and velocity in shock—Heated oxygen flows," Appl. Opt. 32, 6090-6103 (1993).
  9. I. Linnerud, P. Kaspersen, T. Jaeger, "Gas monitoring in the process industry using diode laser spectroscopy," Appl. Phys. B, Lasers Opt. 67, 297-305 (1998).
  10. S. Schilt, L. Thevenaz, P. Robert, "Wavelength modulation spectroscopy: Combined frequency and intensity laser modulation ," Appl. Opt. 42, 6728-6738 (2003).
  11. S. Schilt, L. Thevenaz, "Experimental method based on wavelength modulation spectroscopy for the characterization of semiconductor lasers under direct modulation," Appl. Opt. 43, 4446-4453 (2004).
  12. H. Li, G. B. Rieker, X. Liu, J. B. Jeffries, R. K. Hanson, "Extension of wavelength-modulation spectroscopy to large modulation depth for diode laser absorption measurements in high-pressure gases," Appl. Opt. 45, 1052-1061 (2006).
  13. G. B. Reiker, J. B. Jeffries, R. K. Hanson, "Calibration free wavelength modulation spectroscopy for measurement of gas temperature and concentration in harsh environments," Appl. Opt. 48, 5546-5560 (2009).
  14. K. Duffin, A. J. McGettrick, W. Johnstone, G. Stewart, D. G. Moodie, "Tunable diode laser spectroscopy with wavelength modulation: A calibration-free approach to the recovery of absolute gas absorption line shapes," J. Lightw. Technol. 25, 3114-3125 (2007).
  15. A. J. McGettrick, K. Duffin, W. Johnstone, G. Stewart, D. G. Moodie, "Tunable diode laser spectroscopy with wavelength modulation: A phasor decomposition method for calibration free measurements of gas concentration and pressure," J. Lightw. Technol. 26, 432-440 (2008).
  16. W. Johnstone, A. J. McGettrick, K. Duffin, A. Cheung, G. Stewart, "Tunable diode laser spectroscopy for industrial process applications: System characterisation in conventional and new approaches," IEEE Sens. J. 8, 1079-1088 (2008).
  17. A. J. McGettrick, W. Johnstone, R. Cunningham, J. Black, "Tunable diode laser spectroscopy: Calibration free measurements of gas composition at elevated temperature and pressure," J. Lightw. Technol. 27, 3150-3161 (2009) DOI: 10.1109/JLT.2008.2008729.
  18. G. Stewart, W. Johnstone, J. Bain, K. Ruxton, K. Duffin, "Recovery of absolute gas absorption line shapes with tunable diode laser spectroscopy: Part 1. Theoretical analysis," J. Lightw. Technol. .
  19. H. Wahlquist, "Modulation broadening of unsaturated Lorentzian lines," J. Chem. Phys. 35, 1708-1710 (1961).
  20. W. Jin, Y. Z. Xu, M. S. Demokan, G. Stewart, "Investigation of interferometric noise in fibre optic gas sensors using wavelength modulation spectroscopy," Appl. Opt. 36, 7239-7246 (1997).
  21. L. S. Rothman, "The HITRAN 2004 molecular spectroscopic database," J. Quantitative Spectrosc. Radiative Transf. 96, 139-204 (2005).
  22. A. L. Chakraborty, K. Ruxton, W. Johnstone, M. Lengden, K. Duffin, "Elimination of residual amplitude modulation in tunable diode laser wavelength modulation spectroscopy using an optical fiber delay line," Opt. Exp. 17, 9602-9607 (2009).
  23. A. L. Chakraborty, K. Ruxton, W. Johnstone, "Influence of the wavelength dependence of fiber couplers on the background signal in wavelength modulation spectroscopy with RAM-nulling," Opt. Exp. 18, 267-280 (2009).
  24. P. C. Hobbs, "Ultra-sensitive laser measurements without tears," Appl. Opt. 36, 903-920 (1997).
  25. M. Angelmahr, A. Miklos, P. Hess, "Wavelength- and amplitude-modulated photoacoustics: Comparison of simulated and measured spectra of higher harmonics," Appl. Opt. 47, 2806-2812 (2008).
  26. S. Schilt, L. Thevenaz, "Wavelength modulation photoacoustic spectroscopy: Theoretical description and experimental results ," Infrared Phys. Technol. 48, 154-162 (2006).

2009 (4)

G. B. Reiker, J. B. Jeffries, R. K. Hanson, "Calibration free wavelength modulation spectroscopy for measurement of gas temperature and concentration in harsh environments," Appl. Opt. 48, 5546-5560 (2009).

A. J. McGettrick, W. Johnstone, R. Cunningham, J. Black, "Tunable diode laser spectroscopy: Calibration free measurements of gas composition at elevated temperature and pressure," J. Lightw. Technol. 27, 3150-3161 (2009) DOI: 10.1109/JLT.2008.2008729.

A. L. Chakraborty, K. Ruxton, W. Johnstone, M. Lengden, K. Duffin, "Elimination of residual amplitude modulation in tunable diode laser wavelength modulation spectroscopy using an optical fiber delay line," Opt. Exp. 17, 9602-9607 (2009).

A. L. Chakraborty, K. Ruxton, W. Johnstone, "Influence of the wavelength dependence of fiber couplers on the background signal in wavelength modulation spectroscopy with RAM-nulling," Opt. Exp. 18, 267-280 (2009).

2008 (3)

M. Angelmahr, A. Miklos, P. Hess, "Wavelength- and amplitude-modulated photoacoustics: Comparison of simulated and measured spectra of higher harmonics," Appl. Opt. 47, 2806-2812 (2008).

A. J. McGettrick, K. Duffin, W. Johnstone, G. Stewart, D. G. Moodie, "Tunable diode laser spectroscopy with wavelength modulation: A phasor decomposition method for calibration free measurements of gas concentration and pressure," J. Lightw. Technol. 26, 432-440 (2008).

W. Johnstone, A. J. McGettrick, K. Duffin, A. Cheung, G. Stewart, "Tunable diode laser spectroscopy for industrial process applications: System characterisation in conventional and new approaches," IEEE Sens. J. 8, 1079-1088 (2008).

2007 (1)

K. Duffin, A. J. McGettrick, W. Johnstone, G. Stewart, D. G. Moodie, "Tunable diode laser spectroscopy with wavelength modulation: A calibration-free approach to the recovery of absolute gas absorption line shapes," J. Lightw. Technol. 25, 3114-3125 (2007).

2006 (2)

H. Li, G. B. Rieker, X. Liu, J. B. Jeffries, R. K. Hanson, "Extension of wavelength-modulation spectroscopy to large modulation depth for diode laser absorption measurements in high-pressure gases," Appl. Opt. 45, 1052-1061 (2006).

S. Schilt, L. Thevenaz, "Wavelength modulation photoacoustic spectroscopy: Theoretical description and experimental results ," Infrared Phys. Technol. 48, 154-162 (2006).

2005 (1)

L. S. Rothman, "The HITRAN 2004 molecular spectroscopic database," J. Quantitative Spectrosc. Radiative Transf. 96, 139-204 (2005).

2004 (2)

S. Schilt, L. Thevenaz, "Experimental method based on wavelength modulation spectroscopy for the characterization of semiconductor lasers under direct modulation," Appl. Opt. 43, 4446-4453 (2004).

P. W. Werle, P. Mazzinghi, F. D'Amato, M. De Rosa, K. Maurer, F. Slemr, "Signal processing and calibration procedures for in situ diode laser absorption spectroscopy ," Spectrochimica Acta A 60, 1685-1705 (2004).

2003 (1)

2000 (1)

1998 (2)

I. Linnerud, P. Kaspersen, T. Jaeger, "Gas monitoring in the process industry using diode laser spectroscopy," Appl. Phys. B, Lasers Opt. 67, 297-305 (1998).

P. Werle, "A review of recent advances in semiconductor laser based gas monitors," Spectrochimica Acta A, Mol. Biomol. Spectrosc. 54, 197-236 (1998).

1997 (2)

1994 (1)

1993 (1)

1992 (1)

1981 (1)

J. Reid, D. Labrie, "Second-harmonic detection with tunable diode lasers—Comparison of experiment and theory ," Appl. Phys. B, Lasers Opt. 26, 203-210 (1981).

1961 (1)

H. Wahlquist, "Modulation broadening of unsaturated Lorentzian lines," J. Chem. Phys. 35, 1708-1710 (1961).

Appl. Opt. (11)

J. A. Silver, "Frequency-modulation spectroscopy for trace species detection: Theory and comparison among experimental methods," Appl. Opt. 31, 707-717 (1992).

J. M. Supplee, E. A. Whittaker, W. Lenth, "Theoretical description of frequency modulation and wavelength modulation spectroscopy ," Appl. Opt. 33, 6294-6302 (1994).

S. Schilt, L. Thevenaz, P. Robert, "Wavelength modulation spectroscopy: Combined frequency and intensity laser modulation ," Appl. Opt. 42, 6728-6738 (2003).

S. Schilt, L. Thevenaz, "Experimental method based on wavelength modulation spectroscopy for the characterization of semiconductor lasers under direct modulation," Appl. Opt. 43, 4446-4453 (2004).

H. Li, G. B. Rieker, X. Liu, J. B. Jeffries, R. K. Hanson, "Extension of wavelength-modulation spectroscopy to large modulation depth for diode laser absorption measurements in high-pressure gases," Appl. Opt. 45, 1052-1061 (2006).

G. B. Reiker, J. B. Jeffries, R. K. Hanson, "Calibration free wavelength modulation spectroscopy for measurement of gas temperature and concentration in harsh environments," Appl. Opt. 48, 5546-5560 (2009).

D. Richter, D. G. Lancaster, F. K. Tittel, "Development of an automated diode laser based multicomponent gas sensor," Appl. Opt. 39, 4444-4450 (2000).

L. C. Philippe, R. K. Hanson, "Laser diode wavelength—Modulation spectroscopy for simultaneous measurement of temperature, pressure and velocity in shock—Heated oxygen flows," Appl. Opt. 32, 6090-6103 (1993).

W. Jin, Y. Z. Xu, M. S. Demokan, G. Stewart, "Investigation of interferometric noise in fibre optic gas sensors using wavelength modulation spectroscopy," Appl. Opt. 36, 7239-7246 (1997).

P. C. Hobbs, "Ultra-sensitive laser measurements without tears," Appl. Opt. 36, 903-920 (1997).

M. Angelmahr, A. Miklos, P. Hess, "Wavelength- and amplitude-modulated photoacoustics: Comparison of simulated and measured spectra of higher harmonics," Appl. Opt. 47, 2806-2812 (2008).

Appl. Phys. B, Lasers Opt. (2)

J. Reid, D. Labrie, "Second-harmonic detection with tunable diode lasers—Comparison of experiment and theory ," Appl. Phys. B, Lasers Opt. 26, 203-210 (1981).

I. Linnerud, P. Kaspersen, T. Jaeger, "Gas monitoring in the process industry using diode laser spectroscopy," Appl. Phys. B, Lasers Opt. 67, 297-305 (1998).

IEEE Sens. J. (1)

W. Johnstone, A. J. McGettrick, K. Duffin, A. Cheung, G. Stewart, "Tunable diode laser spectroscopy for industrial process applications: System characterisation in conventional and new approaches," IEEE Sens. J. 8, 1079-1088 (2008).

Infrared Phys. Technol. (1)

S. Schilt, L. Thevenaz, "Wavelength modulation photoacoustic spectroscopy: Theoretical description and experimental results ," Infrared Phys. Technol. 48, 154-162 (2006).

J. Chem. Phys. (1)

H. Wahlquist, "Modulation broadening of unsaturated Lorentzian lines," J. Chem. Phys. 35, 1708-1710 (1961).

J. Lightw. Technol. (4)

A. J. McGettrick, W. Johnstone, R. Cunningham, J. Black, "Tunable diode laser spectroscopy: Calibration free measurements of gas composition at elevated temperature and pressure," J. Lightw. Technol. 27, 3150-3161 (2009) DOI: 10.1109/JLT.2008.2008729.

G. Stewart, W. Johnstone, J. Bain, K. Ruxton, K. Duffin, "Recovery of absolute gas absorption line shapes with tunable diode laser spectroscopy: Part 1. Theoretical analysis," J. Lightw. Technol. .

K. Duffin, A. J. McGettrick, W. Johnstone, G. Stewart, D. G. Moodie, "Tunable diode laser spectroscopy with wavelength modulation: A calibration-free approach to the recovery of absolute gas absorption line shapes," J. Lightw. Technol. 25, 3114-3125 (2007).

A. J. McGettrick, K. Duffin, W. Johnstone, G. Stewart, D. G. Moodie, "Tunable diode laser spectroscopy with wavelength modulation: A phasor decomposition method for calibration free measurements of gas concentration and pressure," J. Lightw. Technol. 26, 432-440 (2008).

J. Quantitative Spectrosc. Radiative Transf. (1)

L. S. Rothman, "The HITRAN 2004 molecular spectroscopic database," J. Quantitative Spectrosc. Radiative Transf. 96, 139-204 (2005).

Opt. Exp. (2)

A. L. Chakraborty, K. Ruxton, W. Johnstone, M. Lengden, K. Duffin, "Elimination of residual amplitude modulation in tunable diode laser wavelength modulation spectroscopy using an optical fiber delay line," Opt. Exp. 17, 9602-9607 (2009).

A. L. Chakraborty, K. Ruxton, W. Johnstone, "Influence of the wavelength dependence of fiber couplers on the background signal in wavelength modulation spectroscopy with RAM-nulling," Opt. Exp. 18, 267-280 (2009).

Sens. Actuat. B, Chem. (1)

G. Stewart, C. Tandy, D. Moodie, M. A. Morante, F. Dong, "Design of a fibre optic multipoint sensor for gas detection," Sens. Actuat. B, Chem. 51, 227-232 ( 1998).

Spectrochimica Acta A (1)

P. W. Werle, P. Mazzinghi, F. D'Amato, M. De Rosa, K. Maurer, F. Slemr, "Signal processing and calibration procedures for in situ diode laser absorption spectroscopy ," Spectrochimica Acta A 60, 1685-1705 (2004).

Spectrochimica Acta A, Mol. Biomol. Spectrosc. (1)

P. Werle, "A review of recent advances in semiconductor laser based gas monitors," Spectrochimica Acta A, Mol. Biomol. Spectrosc. 54, 197-236 (1998).

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