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Environmental Monitoring - using diode-laser-based spectroscopic techniques

Publiceringsår: 2004
Språk: Engelska
Sidor: 184
Publikation/Tidskrift/Serie: Lund Reports in Atomic Physics
Volym: LRAP-329
Dokumenttyp: Doktorsavhandling
Förlag: Atomic Phys. Div. P.O, Box 118 SE- 22363 Lund,
Ytterligare information: Article: J. Sandsten, U. Gustafsson, and G. Somesfalean, Single aerosol particle sizing and identification using a coupled-cavity diode laser, Optics Communications 168, 17-24 (1999). Article: U. Gustafsson, G. Somesfalean, J. Alnis, and S. Svanberg, Frequency modulation spectroscopy with blue diode lasers, Applied Optics 39, 3774-3780 (2000). Article: G. Somesfalean, J. Alnis, U. Gustafsson, H. Edner, and S. Svanberg, Long-path monitoring of NO2 with a 635 nm diode laser using frequency modulation spectroscopy, Submitted. Article: J. Alnis, U. Gustafsson, G. Somesfalean, and S. Svanberg, Sum-frequency generation with a blue diode laser for mercury spectroscopy at 254 nm, Applied Physics Letters 76, 1234-1236 (2000). Article: G. Somesfalean, Z. G. Zhang, M. Sjöholm, and S. Svanberg, All-diode-laser ultraviolet absorption spectroscopy for sulfur dioxide detection, Submitted. Article: M. Sjöholm, G. Somesfalean, J. Alnis, S. Andersson-Engels, and S. Svanberg, Analysis of gas dispersed in scattering media, Optics Letters 26, 16-18 (2001). Article: G. Somesfalean, M. Sjöholm, J. Alnis, C. af Klinteberg, S. Andersson-Engels, and S. Svanberg, Concentration measurement of gas embedded in scattering media by employing absorption and time-resolved laser spectroscopy, Applied Optics 41, 3538-3544 (2002). Article: J. Alnis, B. Andersson, M. Sjöholm, G. Somesfalean, and S. Svanberg, Laser spectroscopy on free molecular oxygen dispersed in wood materials, Applied Physics B 77, 691-695 (2003). Article: G. Somesfalean, M. Sjöholm, L. Persson, H. Gao, T. Svensson, and S. Svanberg, Spectroscopic gas analysis using a new temporal gas correlation technique, Submitted.

Sammanfattning

Monitoring of environmental gases is necessary to understand the complex processes governing global warming and the impact of pollutant emissions related to human activity. Diode-laser-based spectroscopic techniques, being robust and affordable, have a great potential to become an industrially well-established technology for environmental sensing. This thesis deals with the further development of these techniques, demonstrated in several applications to atmospheric gas detection and sensing.

The accessible spectral range of tunable diode lasers was extended by use of sum-frequency generation. High-resolution ultraviolet spectroscopy of mercury isotopes around 254 nm was performed on low-pressure cells as well as at atmospheric pressure. Ultraviolet radiation around 300 nm, utilized for monitoring of sulfur dioxide and studies of the pressure dependence of the absorption spectrum, was produced using a sum-frequency generation scheme employing a blue and a near-infrared diode laser.

Detection sensitivity was improved by several orders of magnitude by employing frequency modulation techniques. This was demonstrated with blue continuous-wave diode lasers in measurements on ground state potassium atoms, and lead atoms in very weakly populated meta-stable states. In the red spectral region, traffic-generated emission of nitrogen dioxide was monitored in situ using long path absorption at a wavelength around 635 nm.

A new temporal gas-correlation scheme was developed, which overcomes the intrinsic multimode and mode-jump behaviour of diode lasers. The concentration of a gas under study is determined by temperature tuning the wavelength of a diode laser across an absorption band of the gas, and by simultaneous temporal correlation of the detected signal with the signal from a known reference gas concentration. No knowledge of the exact spectrum is needed. The method was tested in diffusion related measurements.

A novel technique for analysis of free gas in scattering media by use of absorption spectroscopy, GASMAS, was introduced. The sharp absorption features of the gas, contrasted to the very slow wavelength dependence of the bulk material, can be picked up by use of modulation techniques. Dispersed molecular oxygen embedded in various natural and man-made porous materials was detected and measured. The gas concentration was determined by combining absorption and time-resolved laser spectroscopy measurements. Investigations were performed to assess the internal gas pressure and gas diffusion characteristics.

A new single-aerosol particle detector using a coupled-cavity diode laser was developed. Simultaneous size and shape determination was demonstrated by recording of the optical extinction and a diffraction image in the near-forward scattered light.

Disputation

2004-11-26
13:15
Fysiska institutionen, Hörsal B, Lunds Tekniska Högskola
  • Frank Tittel (Prof)

Nyckelord

  • Physics and Astronomy
  • Diode-laser spectroscopy
  • frequency-modulation spectroscopy
  • frequency conversion
  • diffraction
  • scattering
  • Electromagnetism
  • acoustics
  • akustik
  • optik
  • absorption spectroscopy
  • Elektromagnetism
  • optics
  • Fysicumarkivet A:2004:Somesfalean

Övriga

  • Stefan Andersson-Engels (Prof)
  • ISSN: ISSN 0281-2762
  • ISBN: 91-628-6286-3

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