Abstract

This paper describes the design and performance of a tunable diode laser system, incorporating a multipass absorption cell to allow determination of water concentration below 10 ppb and carbon dioxide concentration below 1 ppb in nitrogen semiconductor gas. The cell is used with a tunable Pb-salt diode laser spectrometer frequency locked to a first derivative error signal from an intense vibration–rotation molecular absorption line. Sample concentrations are monitored in the second derivative mode, and the system automatically compensates for laser intensity fluctuations. A flowing gas method is used to minimize adsorption/desorption effects from the sample cell walls.

© 1989 Optical Society of America

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References

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  1. Anon., “The Big Demands on Specialty Gases,” Chem. Week 26 (21Sept.1983).
  2. F. W. Giacobbe, G. S. Khan, “Production of Ultra-High Purity Nitrogen,” Solid State Technol.77 (July1987).
  3. J. U. White, J. Opt. Soc. Am. 32, 285 (1942).
    [CrossRef]
  4. R. E. Shetter et al., “Temperature Variable Long Path Cell for Absorption Measurements,” Rev. Sci. Instrum. 58, 1427–1428 (1987).
    [CrossRef]
  5. G. Guelachvili, K. N. Rao, Handbook of Infrared Standards (Academic, Orlando, FL, 1986).
  6. Laser Analytics, Inc., Reprint List.
  7. E. D. Hinckley, Ed., Laser Monitoring of the Atmosphere (Springer-Verlag, New York, 1976).
    [CrossRef]
  8. G. Restelli, F. Capellani, “Calibration Technique for IR-Laser Second Derivative Monitoring of some Trace Gases in Tropospheric Air,” Appl. Opt. 24, 2480–2481 (1985).
    [CrossRef] [PubMed]
  9. J. A. Mucha, “Tunable Diode Laser Measurements in Water Vapor Line Parameters in the 6-μm Spectral Region,” Appl. Spectrosc. 36, 141–147 (1982).
    [CrossRef]
  10. J. A. Mucha, “Standard Addition Technique for Quantitative Trace Gas Analysis Using Derivative Infrared Diode Laser Spectroscopy,” Appl. Spectrosc. 36, 393–399 (1982).
    [CrossRef]
  11. Laser Analytics, Inc., Internal Report.

1987 (2)

F. W. Giacobbe, G. S. Khan, “Production of Ultra-High Purity Nitrogen,” Solid State Technol.77 (July1987).

R. E. Shetter et al., “Temperature Variable Long Path Cell for Absorption Measurements,” Rev. Sci. Instrum. 58, 1427–1428 (1987).
[CrossRef]

1985 (1)

1982 (2)

1942 (1)

Capellani, F.

Giacobbe, F. W.

F. W. Giacobbe, G. S. Khan, “Production of Ultra-High Purity Nitrogen,” Solid State Technol.77 (July1987).

Guelachvili, G.

G. Guelachvili, K. N. Rao, Handbook of Infrared Standards (Academic, Orlando, FL, 1986).

Khan, G. S.

F. W. Giacobbe, G. S. Khan, “Production of Ultra-High Purity Nitrogen,” Solid State Technol.77 (July1987).

Mucha, J. A.

Rao, K. N.

G. Guelachvili, K. N. Rao, Handbook of Infrared Standards (Academic, Orlando, FL, 1986).

Restelli, G.

Shetter, R. E.

R. E. Shetter et al., “Temperature Variable Long Path Cell for Absorption Measurements,” Rev. Sci. Instrum. 58, 1427–1428 (1987).
[CrossRef]

White, J. U.

Appl. Opt. (1)

Appl. Spectrosc. (2)

J. Opt. Soc. Am. (1)

Rev. Sci. Instrum. (1)

R. E. Shetter et al., “Temperature Variable Long Path Cell for Absorption Measurements,” Rev. Sci. Instrum. 58, 1427–1428 (1987).
[CrossRef]

Solid State Technol. (1)

F. W. Giacobbe, G. S. Khan, “Production of Ultra-High Purity Nitrogen,” Solid State Technol.77 (July1987).

Other (5)

Laser Analytics, Inc., Internal Report.

G. Guelachvili, K. N. Rao, Handbook of Infrared Standards (Academic, Orlando, FL, 1986).

Laser Analytics, Inc., Reprint List.

E. D. Hinckley, Ed., Laser Monitoring of the Atmosphere (Springer-Verlag, New York, 1976).
[CrossRef]

Anon., “The Big Demands on Specialty Gases,” Chem. Week 26 (21Sept.1983).

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Figures (6)

Fig. 1
Fig. 1

Outline of basic cell dimensions (external side view). Pressure readouts are located at point A, and thermocouples are located at points B, C, and D.

Fig. 2
Fig. 2

Three Invar rods A (only two shown) were bolted to a flange containing three dowel pins B (only two shown). These were allowed to slide with respect to the rear end cap C. This configuration allowed thermal expansion of the stainless steel cell body while holding the optics on a rigid Invar frame.

Fig. 3
Fig. 3

Dual beam Pb-salt diode laser spectrometer was interfaced to the cell using transfer optics. Two beams, split at a ZnSe beam splitter, went through a reference gas cell and the sample cell to a dual element Ge:Cu detector. Laser mode selection occurred at a 0.5-m Czerny-Turner-type monochromator.

Fig. 4
Fig. 4

Electrical schematic.

Fig. 5
Fig. 5

Second derivative scan of H2O line.

Fig. 6
Fig. 6

H2O calibration curve.

Equations (3)

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R = I s / I r .
R c = R × 1 / L × [ 295 / ( T + 273 ) ] × N ,
C = a + b R c + c R c 2 .

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