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Environmental Monitoring - using diode-laser-based spectroscopic techniques

Somesfalean, Gabriel LU (2004) In Lund Reports in Atomic Physics LRAP-329.
Abstract
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... (More)
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. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Prof Tittel, Frank, USA
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Diode-laser spectroscopy, frequency-modulation spectroscopy, frequency conversion, diffraction, scattering, Electromagnetism, acoustics, akustik, optik, absorption spectroscopy, Elektromagnetism, optics, Fysicumarkivet A:2004:Somesfalean
in
Lund Reports in Atomic Physics
volume
LRAP-329
pages
184 pages
publisher
Atomic Physics, Department of Physics, Lund University
defense location
Fysiska institutionen, Hörsal B, Lunds Tekniska Högskola
defense date
2004-11-26 13:15
ISSN
0281-2762
ISBN
91-628-6286-3
language
English
LU publication?
yes
id
88082dd1-b80e-4562-bd1e-764e6bdbdf9f (old id 467637)
date added to LUP
2007-10-01 15:05:09
date last changed
2016-09-19 08:44:54
@phdthesis{88082dd1-b80e-4562-bd1e-764e6bdbdf9f,
  abstract     = {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.<br/><br>
<br/><br>
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.<br/><br>
<br/><br>
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.<br/><br>
<br/><br>
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.<br/><br>
<br/><br>
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.<br/><br>
<br/><br>
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.},
  author       = {Somesfalean, Gabriel},
  isbn         = {91-628-6286-3},
  issn         = {0281-2762},
  keyword      = {Diode-laser spectroscopy,frequency-modulation spectroscopy,frequency conversion,diffraction,scattering,Electromagnetism,acoustics,akustik,optik,absorption spectroscopy,Elektromagnetism,optics,Fysicumarkivet A:2004:Somesfalean},
  language     = {eng},
  pages        = {184},
  publisher    = {Atomic Physics, Department of Physics, Lund University},
  school       = {Lund University},
  series       = {Lund Reports in Atomic Physics},
  title        = {Environmental Monitoring - using diode-laser-based spectroscopic techniques},
  volume       = {LRAP-329},
  year         = {2004},
}