| 1. |
- Guan, Zuguang, et al.
(författare)
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Gas analysis within remote porous targets using LIDAR multi-scatter techniques
- 2008
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Ingår i: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 93:2-3, s. 657-663
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Tidskriftsartikel (refereegranskat)abstract
- Light detection and ranging (LIDAR) experiments are normally pursued for range resolved atmospheric gas measurements or for analysis of solid target surfaces using fluorescence of laser-induced breakdown spectroscopy. In contrast, we now demonstrate the monitoring of free gas enclosed in pores of materials, subject to impinging laser radiation, employing the photons emerging back to the surface laterally of the injection point after penetrating the medium in heavy multiple scattering processes. The directly reflected light is blocked by a beam stop. The technique presented is a remote version of the newly introduced gas in scattering media absorption spectroscopy (GASMAS) technique, which so far was pursued with the injection optics and the detector in close contact with the sample. Feasibility measurements of LIDAR-GASMAS on oxygen in polystyrene foam were performed at a distance of 6 m. Multiple-scattering induced delays of the order of 50 ns, which corresponds to 15 m optical path length, were observed. First extensions to a range of 60 m are discussed. Remote observation of gas composition anomalies in snow using differential absorption LIDAR (DIAL) may find application in avalanche victim localization or for leak detection in snow-covered natural gas pipelines. Further, the techniques may be even more useful for short-range, non-intrusive GASMAS measurements, e.g., on packed food products.
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| 2. |
- Guan, Zuguang, et al.
(författare)
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LIDAR technique for Remote Gas Analysis in Solid Scattering Media
- 2009
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Ingår i: Asia Optical Fiber Communication & Optoelectronic Exposition & Conference, 2008. AOE 2008.. - 9781557528636
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Konferensbidrag (refereegranskat)abstract
- LIDAR techniques are used to measure gases in solid scattering media remotely, by analyzing the differential absorption observed in the multiple scattering light. The gas exchange (O-2/N-2) in polystyrene foam is monitored. (C)2008 Optical Society of America
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| 3. |
- Guan, Zuguang, et al.
(författare)
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Quasi zero-background tunable diode laser absorption spectroscopy employing a balanced Michelson interferometer.
- 2008
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Ingår i: Optics Express. - 1094-4087. ; 16:26, s. 21714-21720
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Tidskriftsartikel (refereegranskat)abstract
- Tunable diode laser spectroscopy (TDLS) normally observes small fractional absorptive reductions in the light flux. We show, that instead a signal increase on a zero background can be obtained. A Michelson interferometer, which is initially balanced out in destructive interference, is perturbed by gas absorption in one of its arms. Both theoretical analysis and experimental demonstration show that the proposed zero-background TDLS can improve the achievable signal-to-noise ratio.
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| 4. |
- Lewander, Märta, et al.
(författare)
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Clinical system for non-invasive in situ monitoring of gases in the human paranasal sinuses
- 2009
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Ingår i: Optics Express. - 1094-4087. ; 17:13, s. 10849-10863
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Tidskriftsartikel (refereegranskat)abstract
- We present a portable system for non-invasive, simultaneous sensing of molecular oxygen (O-2) and water vapor (H2O) in the human paranasal cavities. The system is based on high-resolution tunable diode laser spectroscopy (TDLAS) and digital wavelength modulation spectroscopy (dWMS). Since optical interference and non-ideal tuning of the diode lasers render signal processing complex, we focus on Fourier analysis of dWMS signals and procedures for removal of background signals. Clinical data are presented, and exhibit a significant improvement in signal-to-noise with respect to earlier work. The in situ detection limit, in terms of absorption fraction, is about 5 x 10(-5) for oxygen and 5 x 10(-4) for water vapor, but varies between patients due to differences in light attenuation. In addition, we discuss the use of water vapor as a reference in quantification of in situ oxygen concentration in detail. In particular, light propagation aspects are investigated by employing photon time-of-flight spectroscopy. (C) 2009 Optical Society of America
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| 5. |
- Lewander, Märta, et al.
(författare)
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Food monitoring based on diode laser gas spectroscopy
- 2008
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Ingår i: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 93, s. 619-625
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Tidskriftsartikel (refereegranskat)abstract
- Abstract Food is frequently packed in a controlled environment of gas, in order to extend shelf life. It is of great importance to be able to monitor the status of the packed food to ensure quality. We demonstrate a technique to monitor the gas inside packages non-intrusively by using a laser spectroscopicmethod in scattering solid materials. The technique named GASMAS (GAs in Scattering Media Absorption Spectroscopy) is based on tunable diode laser absorption spectroscopy and relies on the fact that free gas inside solid materials absorbs much sharper spectrally than the bulk material. Results from time dependent measurements of molecular oxygen and water vapour in packages of minced meat, bake-off bread, and the headspace of a milk carton are presented. We show that the technique allows gas measurements inside the food through the package, and assessment of the integrity of the package.
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| 6. |
- Lewander, Märta, et al.
(författare)
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Gas Analysis in Food Packages Using Tunable Diode Laser Spectroscopy
- 2009
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Ingår i: Asia Optical Fiber Communication & Optoelectronic Exposition & Conference, 2008. AOE 2008.. - 9781557528636
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Konferensbidrag (refereegranskat)abstract
- Gas inside packed food is monitored by a technique named GASMAS, GAs in Scattering Media Absorption Spectroscopy. The sharp gas absorption line in contrast to the broadband bulk absorption enables gas detection in situ. (C)2008 Optical Society of America
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| 7. |
- Persson, Linda, et al.
(författare)
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Gas monitoring in human sinuses using tunable diode laser spectroscopy
- 2007
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Ingår i: Journal of Biomedical Optics. - 1083-3668. ; 12:5
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate a novel nonintrusive technique based on tunable diode laser absorption spectroscopy to investigate human sinuses in vivo. The technique relies on the fact that free gases have spectral imprints that are about 10.000 times sharper than spectral structures of the surrounding tissue. Two gases are detected; molecular oxygen at 760 nm and water vapor at 935 nm. Light is launched fiber optically into the tissue in close proximity to the particular maxillary sinus under study. When investigating the frontal sinuses, the fiber is positioned onto the caudal part of the frontal bone. Multiply scattered light in both cases is detected externally by a handheld probe. Molecular oxygen is detected in the maxillary sinuses on 11 volunteers, of which one had constantly recurring sinus problems. Significant oxygen absorption imprint differences can be observed between different volunteers and also left-right asymmetries. Water vapor can also be detected, and by normalizing the oxygen signal on the water vapor signal, the sinus oxygen concentration can be assessed. Gas exchange between the sinuses and the nasal cavity is also successfully demonstrated by flushing nitrogen through the nostril. Advantages over current ventilation assessment methods using ionizing radiation are pointed out.
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| 8. |
- Persson, Linda, et al.
(författare)
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Non-intrusive optical study of gas and its exchange in human maxillary sinuses - art. no. 662804
- 2007
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Ingår i: Diagnostic Optical Spectroscopy in Biomedicine IV. - : SPIE. - 1996-756X .- 0277-786X. ; 6628, s. 62804-62804
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Konferensbidrag (refereegranskat)abstract
- We demonstrate a novel non-intrusive technique based on tunable diode laser absorption spectroscopy to investigate human maxillary sinuses in vivo. The technique relies on the fact that free gases have much sharper absorption features (typical a few GHz) than the surrounding tissue. Molecular oxygen was detected at 760 nm. Volunteers have been investigated by injecting near-infrared light fibre-optically in contact with the palate inside the mouth. The multiply scattered light was detected externally by a handheld probe on and around the cheek bone. A significant signal difference in oxygen imprint was observed when comparing volunteers with widely different anamnesis regarding maxillary sinus status. Control measurements through the hand and through the cheek below the cheekbone were also performed to investigate any possible oxygen offset in the setup. These provided a consistently non-detectable signal level. The passages between the nasal cavity and the maxillary sinuses were also non-intrusively optically studied, to the best of our knowledge for the first time. These measurements provide information on the channel conductivity which may prove useful in facial sinus diagnostics. The results suggest that a clinical trial together with an ear-nose-throat (ENT) clinic should be carried out to investigate the clinical use of the new technique.
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| 9. |
- Persson, Linda, et al.
(författare)
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Simultaneous detection of molecular oxygen and water vapor in the tissue optical window using tunable diode laser spectroscopy
- 2008
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Ingår i: Applied Optics. - 2155-3165. ; 47:12, s. 2028-2034
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Tidskriftsartikel (refereegranskat)abstract
- We report on a newly developed diode-laser spectroscopic system for gas detection in scattering media. Two pigtailed diode lasers are used, operating in a wavelength modulation scheme, to simultaneously detect molecular oxygen at 760 nm and water vapour at 935 nm within the tissue optical window (600 nm to 1.3 μm). Different modulation frequencies are used to distinguish between the two wavelengths. No crosstalk can be observed between the gas contents of the two gas channels. The system is made compact by using a computer board and performing software based lock-in detection. The noise floor obtained corresponds to an absorption fraction of about 6 · 10−5 for both oxygen and water vapour. The power of the technique is illustrated by preliminary results from a clinical trial investigating the human sinuses.
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