Abstract

What we believe to be a novel multipass, acoustically open photoacoustic detector designed for fast-response, high-sensitivity detection of trace gases and pollutants in the atmosphere is demonstrated. The acoustic pulses generated by the absorption of the light pulses of a tunable optical parametric oscillator by target molecules are detected by an ultrasonic sensor at 40 kHz. The photoacoustic signal is enhanced by an optical multipass arrangement and by concentration of the acoustic energy to the surface of the ultrasonic sensor. The detection sensitivity, estimated from CO2 measurements around a 2  μm wavelength, is 3.3×109  W  cm1.

© 2006 Optical Society of America

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References

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  1. M. W. Sigrist, Air Monitoring by Spectroscopic Techniques (Wiley, 1994).
  2. F. G. C. Bijnen, J. Reuss, and F. J. M. Harren, "Geometrical optimization of a longitudinal resonant photoacoustic cell for sensitive and fast trace gas detection," Rev. Sci. Instrum. 67, 2914-2923 (1996).
    [CrossRef]
  3. A. Miklós and P. Hess, "Modulated and pulsed photoacoustics in trace gas analysis," Anal. Chem. 72, 30A-37A (2000).
    [CrossRef] [PubMed]
  4. S. Bernegger and M. W. Sigrist, "CO-laser photoacoustic spectroscopy of gases and vapors for trace gas analysis," Infrared Phys. 30, 375-429 (1990).
    [CrossRef]
  5. C. Brand, A. Winkler, P. Hess, A. Miklós, Z. Bozóki, and J. Sneider, "Pulsed-laser excitation of acoustic modes in open high-Q photoacoustic resonators for trace gas monitoring: results for C2H4," Appl. Opt. 34, 3257-3266 (1995).
    [CrossRef] [PubMed]
  6. R. Gerlach and N. M. Amer, "Sensitive in situ trace-gas detection by photothermal deflection spectroscopy," Appl. Phys. Lett. 37, 519-521 (1980).
    [CrossRef]
  7. G. Z. Angeli, A. M. Sólyom, A. Miklós, and D. D. Bicanic, "Calibration of a windowless photoacoustic cell for detection of trace gases," Anal. Chem. 64, 155-158 (1992).
    [CrossRef]
  8. M. Harris, G. N. Pearson, D. V. Willets, K. Ridley, P. R. Tapster, and B. Perrett, "Pulsed indirect photoacoustic spectroscopy: application to remote detection of condensed phases," Appl. Opt. 39, 1032-1041 (2000).
    [CrossRef]
  9. B. Perrett, M. Harris, G. N. Pearson, D. V. Willets, and M. C. Pitter, "Remote photoacoustic detection of liquid contamination of a surface," Appl. Opt. 42, 4901-4908 (2003).
    [CrossRef] [PubMed]
  10. E. Huang, D. R. Rowling, T. Whelan, and J. L. Spiesberger, "High-sensitivity photoacoustic leak testing," J. Acoust. Soc. Am. 114, 1926-1933 (2003).
    [CrossRef] [PubMed]
  11. S. Schäfer, A. Miklós, and P. Hess, "Quantitative signal analysis in pulsed resonant photoacoustics," Appl. Opt. 36, 3202-3211 (1997).
    [CrossRef] [PubMed]
  12. G.-C. Liang, H.-H. Liu, A. H. Kung, A. Mohacsi, A. Miklos, and P. Hess, "Photoacoustic trace detection of methane using compact solid-state lasers," J. Phys. Chem. A 104, 10179-10183 (2000).
    [CrossRef]
  13. A. Miklós, Ch.-H. Lim, W. W. Hsiang, G.-C. Liang, A. H. Kung, A. Schmohl, and P. Hess, "Photoacoustic measurement of methane concentration using a compact pulsed optical parametric oscillator," Appl. Opt. 41, 2985-2993 (2002).
    [CrossRef] [PubMed]
  14. J. Ng, A. H. Kung, A. Miklós, and P. Hess, "Sensitive wavelength-modulated photoacoustic spectroscopy with a pulsed optical parametric oscillator," Opt. Lett. 29, 1206-1208 (2004).
    [CrossRef] [PubMed]
  15. A. A. Kosterev, Yu. A. Bakhirkin, R. F. Curl, and F. K. Tittel, "Quartz-enhanced photoacoustic spectroscopy," Opt. Lett. 27, 1902-1904 (2002).
    [CrossRef]
  16. A. Miklós, J. Angster, K. Sedlbauer, K. Breuer, and A. H. Kung, "Acoustically open, optically multipass, high frequency photoacoustic detector for free-field trace gas measurements," patent pending, German Patent Office, submission number 10 2005 030 151.7-52.
  17. C.-S. Yu and A. H. Kung, "Grazing-incidence periodically poled LiNbO3 optical parametric oscillator," J. Opt. Soc. Am. B 16, 2233-2238 (1999).
    [CrossRef]
  18. A. Miklós, P. Hess, and Z. Bozoki, "Application of acoustic resonators in photoacoustic trace gas analysis and metrology," Rev. Sci. Instrum. 72, 1937-1955 (2001).
    [CrossRef]
  19. A. Schmohl, A. Miklós, and P. Hess, "Detection of ammonia by photoacoustic spectroscopy with semiconductor lasers," Appl. Opt. 41, 1815-1823 (2002).
    [CrossRef] [PubMed]

2004

2003

B. Perrett, M. Harris, G. N. Pearson, D. V. Willets, and M. C. Pitter, "Remote photoacoustic detection of liquid contamination of a surface," Appl. Opt. 42, 4901-4908 (2003).
[CrossRef] [PubMed]

E. Huang, D. R. Rowling, T. Whelan, and J. L. Spiesberger, "High-sensitivity photoacoustic leak testing," J. Acoust. Soc. Am. 114, 1926-1933 (2003).
[CrossRef] [PubMed]

2002

2001

A. Miklós, P. Hess, and Z. Bozoki, "Application of acoustic resonators in photoacoustic trace gas analysis and metrology," Rev. Sci. Instrum. 72, 1937-1955 (2001).
[CrossRef]

2000

G.-C. Liang, H.-H. Liu, A. H. Kung, A. Mohacsi, A. Miklos, and P. Hess, "Photoacoustic trace detection of methane using compact solid-state lasers," J. Phys. Chem. A 104, 10179-10183 (2000).
[CrossRef]

A. Miklós and P. Hess, "Modulated and pulsed photoacoustics in trace gas analysis," Anal. Chem. 72, 30A-37A (2000).
[CrossRef] [PubMed]

M. Harris, G. N. Pearson, D. V. Willets, K. Ridley, P. R. Tapster, and B. Perrett, "Pulsed indirect photoacoustic spectroscopy: application to remote detection of condensed phases," Appl. Opt. 39, 1032-1041 (2000).
[CrossRef]

1999

1997

1996

F. G. C. Bijnen, J. Reuss, and F. J. M. Harren, "Geometrical optimization of a longitudinal resonant photoacoustic cell for sensitive and fast trace gas detection," Rev. Sci. Instrum. 67, 2914-2923 (1996).
[CrossRef]

1995

1992

G. Z. Angeli, A. M. Sólyom, A. Miklós, and D. D. Bicanic, "Calibration of a windowless photoacoustic cell for detection of trace gases," Anal. Chem. 64, 155-158 (1992).
[CrossRef]

1990

S. Bernegger and M. W. Sigrist, "CO-laser photoacoustic spectroscopy of gases and vapors for trace gas analysis," Infrared Phys. 30, 375-429 (1990).
[CrossRef]

1980

R. Gerlach and N. M. Amer, "Sensitive in situ trace-gas detection by photothermal deflection spectroscopy," Appl. Phys. Lett. 37, 519-521 (1980).
[CrossRef]

Amer, N. M.

R. Gerlach and N. M. Amer, "Sensitive in situ trace-gas detection by photothermal deflection spectroscopy," Appl. Phys. Lett. 37, 519-521 (1980).
[CrossRef]

Angeli, G. Z.

G. Z. Angeli, A. M. Sólyom, A. Miklós, and D. D. Bicanic, "Calibration of a windowless photoacoustic cell for detection of trace gases," Anal. Chem. 64, 155-158 (1992).
[CrossRef]

Angster, J.

A. Miklós, J. Angster, K. Sedlbauer, K. Breuer, and A. H. Kung, "Acoustically open, optically multipass, high frequency photoacoustic detector for free-field trace gas measurements," patent pending, German Patent Office, submission number 10 2005 030 151.7-52.

Bakhirkin, Yu. A.

Bernegger, S.

S. Bernegger and M. W. Sigrist, "CO-laser photoacoustic spectroscopy of gases and vapors for trace gas analysis," Infrared Phys. 30, 375-429 (1990).
[CrossRef]

Bicanic, D. D.

G. Z. Angeli, A. M. Sólyom, A. Miklós, and D. D. Bicanic, "Calibration of a windowless photoacoustic cell for detection of trace gases," Anal. Chem. 64, 155-158 (1992).
[CrossRef]

Bijnen, F. G. C.

F. G. C. Bijnen, J. Reuss, and F. J. M. Harren, "Geometrical optimization of a longitudinal resonant photoacoustic cell for sensitive and fast trace gas detection," Rev. Sci. Instrum. 67, 2914-2923 (1996).
[CrossRef]

Bozoki, Z.

A. Miklós, P. Hess, and Z. Bozoki, "Application of acoustic resonators in photoacoustic trace gas analysis and metrology," Rev. Sci. Instrum. 72, 1937-1955 (2001).
[CrossRef]

Bozóki, Z.

Brand, C.

Breuer, K.

A. Miklós, J. Angster, K. Sedlbauer, K. Breuer, and A. H. Kung, "Acoustically open, optically multipass, high frequency photoacoustic detector for free-field trace gas measurements," patent pending, German Patent Office, submission number 10 2005 030 151.7-52.

Curl, R. F.

Gerlach, R.

R. Gerlach and N. M. Amer, "Sensitive in situ trace-gas detection by photothermal deflection spectroscopy," Appl. Phys. Lett. 37, 519-521 (1980).
[CrossRef]

Harren, F. J. M.

F. G. C. Bijnen, J. Reuss, and F. J. M. Harren, "Geometrical optimization of a longitudinal resonant photoacoustic cell for sensitive and fast trace gas detection," Rev. Sci. Instrum. 67, 2914-2923 (1996).
[CrossRef]

Harris, M.

Hess, P.

J. Ng, A. H. Kung, A. Miklós, and P. Hess, "Sensitive wavelength-modulated photoacoustic spectroscopy with a pulsed optical parametric oscillator," Opt. Lett. 29, 1206-1208 (2004).
[CrossRef] [PubMed]

A. Miklós, Ch.-H. Lim, W. W. Hsiang, G.-C. Liang, A. H. Kung, A. Schmohl, and P. Hess, "Photoacoustic measurement of methane concentration using a compact pulsed optical parametric oscillator," Appl. Opt. 41, 2985-2993 (2002).
[CrossRef] [PubMed]

A. Schmohl, A. Miklós, and P. Hess, "Detection of ammonia by photoacoustic spectroscopy with semiconductor lasers," Appl. Opt. 41, 1815-1823 (2002).
[CrossRef] [PubMed]

A. Miklós, P. Hess, and Z. Bozoki, "Application of acoustic resonators in photoacoustic trace gas analysis and metrology," Rev. Sci. Instrum. 72, 1937-1955 (2001).
[CrossRef]

A. Miklós and P. Hess, "Modulated and pulsed photoacoustics in trace gas analysis," Anal. Chem. 72, 30A-37A (2000).
[CrossRef] [PubMed]

G.-C. Liang, H.-H. Liu, A. H. Kung, A. Mohacsi, A. Miklos, and P. Hess, "Photoacoustic trace detection of methane using compact solid-state lasers," J. Phys. Chem. A 104, 10179-10183 (2000).
[CrossRef]

S. Schäfer, A. Miklós, and P. Hess, "Quantitative signal analysis in pulsed resonant photoacoustics," Appl. Opt. 36, 3202-3211 (1997).
[CrossRef] [PubMed]

C. Brand, A. Winkler, P. Hess, A. Miklós, Z. Bozóki, and J. Sneider, "Pulsed-laser excitation of acoustic modes in open high-Q photoacoustic resonators for trace gas monitoring: results for C2H4," Appl. Opt. 34, 3257-3266 (1995).
[CrossRef] [PubMed]

Hsiang, W. W.

Huang, E.

E. Huang, D. R. Rowling, T. Whelan, and J. L. Spiesberger, "High-sensitivity photoacoustic leak testing," J. Acoust. Soc. Am. 114, 1926-1933 (2003).
[CrossRef] [PubMed]

Kosterev, A. A.

Kung, A. H.

J. Ng, A. H. Kung, A. Miklós, and P. Hess, "Sensitive wavelength-modulated photoacoustic spectroscopy with a pulsed optical parametric oscillator," Opt. Lett. 29, 1206-1208 (2004).
[CrossRef] [PubMed]

A. Miklós, Ch.-H. Lim, W. W. Hsiang, G.-C. Liang, A. H. Kung, A. Schmohl, and P. Hess, "Photoacoustic measurement of methane concentration using a compact pulsed optical parametric oscillator," Appl. Opt. 41, 2985-2993 (2002).
[CrossRef] [PubMed]

G.-C. Liang, H.-H. Liu, A. H. Kung, A. Mohacsi, A. Miklos, and P. Hess, "Photoacoustic trace detection of methane using compact solid-state lasers," J. Phys. Chem. A 104, 10179-10183 (2000).
[CrossRef]

C.-S. Yu and A. H. Kung, "Grazing-incidence periodically poled LiNbO3 optical parametric oscillator," J. Opt. Soc. Am. B 16, 2233-2238 (1999).
[CrossRef]

A. Miklós, J. Angster, K. Sedlbauer, K. Breuer, and A. H. Kung, "Acoustically open, optically multipass, high frequency photoacoustic detector for free-field trace gas measurements," patent pending, German Patent Office, submission number 10 2005 030 151.7-52.

Liang, G.-C.

A. Miklós, Ch.-H. Lim, W. W. Hsiang, G.-C. Liang, A. H. Kung, A. Schmohl, and P. Hess, "Photoacoustic measurement of methane concentration using a compact pulsed optical parametric oscillator," Appl. Opt. 41, 2985-2993 (2002).
[CrossRef] [PubMed]

G.-C. Liang, H.-H. Liu, A. H. Kung, A. Mohacsi, A. Miklos, and P. Hess, "Photoacoustic trace detection of methane using compact solid-state lasers," J. Phys. Chem. A 104, 10179-10183 (2000).
[CrossRef]

Lim, Ch.-H.

Liu, H.-H.

G.-C. Liang, H.-H. Liu, A. H. Kung, A. Mohacsi, A. Miklos, and P. Hess, "Photoacoustic trace detection of methane using compact solid-state lasers," J. Phys. Chem. A 104, 10179-10183 (2000).
[CrossRef]

Miklos, A.

G.-C. Liang, H.-H. Liu, A. H. Kung, A. Mohacsi, A. Miklos, and P. Hess, "Photoacoustic trace detection of methane using compact solid-state lasers," J. Phys. Chem. A 104, 10179-10183 (2000).
[CrossRef]

Miklós, A.

J. Ng, A. H. Kung, A. Miklós, and P. Hess, "Sensitive wavelength-modulated photoacoustic spectroscopy with a pulsed optical parametric oscillator," Opt. Lett. 29, 1206-1208 (2004).
[CrossRef] [PubMed]

A. Schmohl, A. Miklós, and P. Hess, "Detection of ammonia by photoacoustic spectroscopy with semiconductor lasers," Appl. Opt. 41, 1815-1823 (2002).
[CrossRef] [PubMed]

A. Miklós, Ch.-H. Lim, W. W. Hsiang, G.-C. Liang, A. H. Kung, A. Schmohl, and P. Hess, "Photoacoustic measurement of methane concentration using a compact pulsed optical parametric oscillator," Appl. Opt. 41, 2985-2993 (2002).
[CrossRef] [PubMed]

A. Miklós, P. Hess, and Z. Bozoki, "Application of acoustic resonators in photoacoustic trace gas analysis and metrology," Rev. Sci. Instrum. 72, 1937-1955 (2001).
[CrossRef]

A. Miklós and P. Hess, "Modulated and pulsed photoacoustics in trace gas analysis," Anal. Chem. 72, 30A-37A (2000).
[CrossRef] [PubMed]

S. Schäfer, A. Miklós, and P. Hess, "Quantitative signal analysis in pulsed resonant photoacoustics," Appl. Opt. 36, 3202-3211 (1997).
[CrossRef] [PubMed]

C. Brand, A. Winkler, P. Hess, A. Miklós, Z. Bozóki, and J. Sneider, "Pulsed-laser excitation of acoustic modes in open high-Q photoacoustic resonators for trace gas monitoring: results for C2H4," Appl. Opt. 34, 3257-3266 (1995).
[CrossRef] [PubMed]

G. Z. Angeli, A. M. Sólyom, A. Miklós, and D. D. Bicanic, "Calibration of a windowless photoacoustic cell for detection of trace gases," Anal. Chem. 64, 155-158 (1992).
[CrossRef]

A. Miklós, J. Angster, K. Sedlbauer, K. Breuer, and A. H. Kung, "Acoustically open, optically multipass, high frequency photoacoustic detector for free-field trace gas measurements," patent pending, German Patent Office, submission number 10 2005 030 151.7-52.

Mohacsi, A.

G.-C. Liang, H.-H. Liu, A. H. Kung, A. Mohacsi, A. Miklos, and P. Hess, "Photoacoustic trace detection of methane using compact solid-state lasers," J. Phys. Chem. A 104, 10179-10183 (2000).
[CrossRef]

Ng, J.

Pearson, G. N.

Perrett, B.

Pitter, M. C.

Reuss, J.

F. G. C. Bijnen, J. Reuss, and F. J. M. Harren, "Geometrical optimization of a longitudinal resonant photoacoustic cell for sensitive and fast trace gas detection," Rev. Sci. Instrum. 67, 2914-2923 (1996).
[CrossRef]

Ridley, K.

Rowling, D. R.

E. Huang, D. R. Rowling, T. Whelan, and J. L. Spiesberger, "High-sensitivity photoacoustic leak testing," J. Acoust. Soc. Am. 114, 1926-1933 (2003).
[CrossRef] [PubMed]

Schäfer, S.

Schmohl, A.

Sedlbauer, K.

A. Miklós, J. Angster, K. Sedlbauer, K. Breuer, and A. H. Kung, "Acoustically open, optically multipass, high frequency photoacoustic detector for free-field trace gas measurements," patent pending, German Patent Office, submission number 10 2005 030 151.7-52.

Sigrist, M. W.

S. Bernegger and M. W. Sigrist, "CO-laser photoacoustic spectroscopy of gases and vapors for trace gas analysis," Infrared Phys. 30, 375-429 (1990).
[CrossRef]

M. W. Sigrist, Air Monitoring by Spectroscopic Techniques (Wiley, 1994).

Sneider, J.

Sólyom, A. M.

G. Z. Angeli, A. M. Sólyom, A. Miklós, and D. D. Bicanic, "Calibration of a windowless photoacoustic cell for detection of trace gases," Anal. Chem. 64, 155-158 (1992).
[CrossRef]

Spiesberger, J. L.

E. Huang, D. R. Rowling, T. Whelan, and J. L. Spiesberger, "High-sensitivity photoacoustic leak testing," J. Acoust. Soc. Am. 114, 1926-1933 (2003).
[CrossRef] [PubMed]

Tapster, P. R.

Tittel, F. K.

Whelan, T.

E. Huang, D. R. Rowling, T. Whelan, and J. L. Spiesberger, "High-sensitivity photoacoustic leak testing," J. Acoust. Soc. Am. 114, 1926-1933 (2003).
[CrossRef] [PubMed]

Willets, D. V.

Winkler, A.

Yu, C.-S.

Anal. Chem.

A. Miklós and P. Hess, "Modulated and pulsed photoacoustics in trace gas analysis," Anal. Chem. 72, 30A-37A (2000).
[CrossRef] [PubMed]

G. Z. Angeli, A. M. Sólyom, A. Miklós, and D. D. Bicanic, "Calibration of a windowless photoacoustic cell for detection of trace gases," Anal. Chem. 64, 155-158 (1992).
[CrossRef]

Appl. Opt.

Appl. Phys. Lett.

R. Gerlach and N. M. Amer, "Sensitive in situ trace-gas detection by photothermal deflection spectroscopy," Appl. Phys. Lett. 37, 519-521 (1980).
[CrossRef]

Infrared Phys.

S. Bernegger and M. W. Sigrist, "CO-laser photoacoustic spectroscopy of gases and vapors for trace gas analysis," Infrared Phys. 30, 375-429 (1990).
[CrossRef]

J. Acoust. Soc. Am.

E. Huang, D. R. Rowling, T. Whelan, and J. L. Spiesberger, "High-sensitivity photoacoustic leak testing," J. Acoust. Soc. Am. 114, 1926-1933 (2003).
[CrossRef] [PubMed]

J. Opt. Soc. Am. B

J. Phys. Chem. A

G.-C. Liang, H.-H. Liu, A. H. Kung, A. Mohacsi, A. Miklos, and P. Hess, "Photoacoustic trace detection of methane using compact solid-state lasers," J. Phys. Chem. A 104, 10179-10183 (2000).
[CrossRef]

Opt. Lett.

Rev. Sci. Instrum.

A. Miklós, P. Hess, and Z. Bozoki, "Application of acoustic resonators in photoacoustic trace gas analysis and metrology," Rev. Sci. Instrum. 72, 1937-1955 (2001).
[CrossRef]

F. G. C. Bijnen, J. Reuss, and F. J. M. Harren, "Geometrical optimization of a longitudinal resonant photoacoustic cell for sensitive and fast trace gas detection," Rev. Sci. Instrum. 67, 2914-2923 (1996).
[CrossRef]

Other

M. W. Sigrist, Air Monitoring by Spectroscopic Techniques (Wiley, 1994).

A. Miklós, J. Angster, K. Sedlbauer, K. Breuer, and A. H. Kung, "Acoustically open, optically multipass, high frequency photoacoustic detector for free-field trace gas measurements," patent pending, German Patent Office, submission number 10 2005 030 151.7-52.

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Figures (6)

Fig. 1
Fig. 1

Periodic train of primary acoustic pulses generated by the absorption of a 3 mm diameter beam of a pulsed laser with 4000 Hz repetition frequency. (a) Pulse train and (b) a single pulse in the train. PA, photoacoustic.

Fig. 2
Fig. 2

Frequency spectrum given by the Fourier transform of the time signal shown in Fig. 1.

Fig. 3
Fig. 3

Schematic views of the MOPAD: (a) the plane of the drawing is normal to the plane of the optical mirrors and contains the acoustic axis, and (b) the plane of the drawing is parallel to the optical mirrors and contains the acoustic axis.

Fig. 4
Fig. 4

View of the MOPAD showing the path of the multiple passes of the laser beam inside the detector.

Fig. 5
Fig. 5

Schematic diagram of the OPO and MOPAD measurement setup. HR, high reflectance; PPLN, periodically poled lithium niobate; CFIR, infrared-grade calcium fluoride.

Fig. 6
Fig. 6

Measured (dotted curve) and simulated (solid curve) photoacoustic spectra of CO2 in ambient air in the 2 μm wavelength region. The left axis is for the measured data. PA, photoacoustic.

Equations (77)

Equations on this page are rendered with MathJax. Learn more.

2   μm
3.3 × 10 9   W   cm 1
CO 2
10   m
SF 6
SF 6
1   mm
1 / r 2
10 50   ns
3   mm
331 m / s
9   μs
110   kHz
3   mm
10   μs
4   kHz
4   kHz
10   μs
17
80   mm
25   mm
5   mm
40   kHz
± 20 °
30   dB
d = 2.44 × ( f λ / D )
λ = 3   mm
f = 25   mm
D = 80   mm
d = 2.3   mm
10   mm
4.1 mm 2 ( π d 2 / 4 )
50   mm × 70   mm = 3500 mm 2
7000 mm 2 / 4.1 mm 2 1700
70   mm × 3   mm
2100 mm 2
4200 mm 2
2 / π
π / 2   to   π / 2
( 2 / π ) × 4200 / 4.1 650
CO 2
LiNbO 3
21   ns
2   μm
4.11   kHz
41.1   kHz
100   kHz
CO 2
CO 2
2   μm
CO 2
CO 2
CO 2
1.7 %
CO 2
CO 2
40   nV
40   nV
CO 2
4964.4 cm 1
25.8   μV
α = 1.67 × 10 5 cm 1
α min = ( 0.04   μV / 25 .8   μV ) × 1.67 × 10 5 cm 1 = 2.6 × 10 8 cm 1
126   mW
S = 3.3 × 10 9   W   cm 1
( S = 1 × 10 9   W   cm 1 )
4964.4 cm 1
557   μV
22.1   μV
0.270   μV
0.040   μV
S closed = 1 × 10 9   W   cm 1
S open = 3.7 × 10 9   W   cm 1
1 mV / Pa
( 100 mV / Pa )
NO 2
SO 2

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