| 1. |
- Huang, Jing, et al.
(författare)
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Gas exchange in fruits related to skin condition and fruit ripening studied with diode laser spectroscopy
- 2016
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Ingår i: Journal of Biomedical Optics. - 1083-3668. ; 21:12
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Tidskriftsartikel (refereegranskat)abstract
- The concentration of the biologically active molecular oxygen gas is of crucial importance for fruits in the metabolic respiration, maturation, and ripening processes. In our study, oxygen content and oxygen transport in fruits, exemplified by apples and guavas, were studied noninvasively by gas in scattering media absorption spectroscopy. The technique is based on the fact that free gases typically have 10,000 times narrower absorption features than the bulk material. The technique was demonstrated in studies of the influence of the fruit skin in regulating the internal oxygen balance, by observing the signal response of the internal oxygen gas to a transient change in the ambient gas concentration on peeled and unpeeled fruits. In addition, the gas exchange rate at different ripening stages was also studied in intact guavas.
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| 2. |
- Jansson, Samuel, et al.
(författare)
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Spatial monitoring of flying insects over a Swedish lake using a continuous-wave lidar system
- 2023
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Ingår i: Royal Society Open Science. - 2054-5703. ; 10:5
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Tidskriftsartikel (refereegranskat)abstract
- We have used a continuous-wave bi-static lidar system based on the Scheimpflug principle in measurements on flying insects above, and in the vicinity of, a small lake located in a forested area in Southern Sweden. The system, which operates on triangulation principles, has a high spatial resolution at close distance, followed by a subsequent decline in resolution further from the sensor, related to the compact system design with a separation of transmitter and receiver by only 0.81 m. Our study showed a strong increase in insect abundance especially at dusk, but also at dawn. Insect numbers decreased over water compared to over land, and larger insects were over-represented over water. Further, the average size of the insects increased at night compared to day time.
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| 3. |
- Larsson, Jim, et al.
(författare)
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Development of a compact multipass oxygen sensor used for gas diffusion studies in opaque media
- 2015
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Ingår i: Applied Optics. - 2155-3165. ; 54:33, s. 9772-9778
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Tidskriftsartikel (refereegranskat)abstract
- A highly scattering porous ceramic sample is employed as a miniature random-scattering multipass gas cell for monitoring of oxygen content in opaque media, that is, wood materials in the present work. Gas in scattering media absorption spectroscopy is used by employing a 760 nm near-infrared laser diode to probe the absorption of molecular oxygen enclosed in the pores of the ceramic material working as the multipass gas cell, with a porosity of 75%. A path length enhancement of approximately 26 times and a signal-to-noise ratio of about 60 were obtained for the ceramic sample used in this work. The gas sensor was then used in a case study of the gas diffusion in wood materials, namely, oak, spruce, and mahogany samples. Differences depending on whether gas diffusion was studied longitudinal or radial to the tree annual rings are demonstrated, with very little gas diffusing in the radial direction. We can also observe that the gas diffusion for the densest material-oak-had the fastest diffusion time, and mahogany, which had the lowest density, showed the slowest diffusion time. (C) 2015 Optical Society of America
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| 4. |
- Lundin, Patrik, et al.
(författare)
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Laser spectroscopic gas concentration measurements in situations with unknown optical path length enabled by absorption line shape analysis
- 2013
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 103:3
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Tidskriftsartikel (refereegranskat)abstract
- The concentrations of molecular oxygen and nitrogen in a gas mixture were determined by their impact on the shape of a water vapor line in the near infrared region using diode laser absorption spectroscopy. The shape of the water vapor line depends on the composition of other gases in the mixture and can therefore be used to deduce the concentration of partner molecules, e. g., oxygen, in the buffer. The method enables gas concentration measurements in situations when the path length is unknown, measurements of many gases simultaneously, and measurements of gases lacking suitable absorption lines. (C) 2013 AIP Publishing LLC.
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| 5. |
- Lundin, Patrik, et al.
(författare)
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Sensitivity enhancement and fringe reduction in tunable diode laser spectroscopy using hemispherical diffusers
- 2017
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 88:5
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Tidskriftsartikel (refereegranskat)abstract
- The use of diffuse, highly reflective optical components, in particular, a hemispherical BaSO4 diffuser, at the point of light injection into non-transparent or turbid media was evaluated as a means to increase the measurement sensitivity of spectroscopic absorption measurements. By performing the light injection from, e.g., an optical fiber through a component designed to make the light diffuse and to reflect (and thereby re-inject) light scattered from the sample, the total amount of light delivered into the sample is increased. Further, the occurrence of possible interference fringes is strongly reduced.
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| 6. |
- Mei, Liang, et al.
(författare)
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Characterization and validation of the frequency-modulated continuous-wave technique for assessment of photon migration in solid scattering media
- 2012
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Ingår i: Applied physics. B, Lasers and optics (Print). - : Springer Nature. - 0946-2171 .- 1432-0649. ; 109:3, s. 467-475
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Tidskriftsartikel (refereegranskat)abstract
- The frequency-modulated continuous-wave (FM-CW) technique, based on the beat signal of a Mach-Zehnder interferometer employing a frequency-ramped light source, is studied for solid scattering media applications. The method is used to evaluate the mean time-of-flight (MTOF) of light traveling in scattering media, specifically polystyrene foams. We assume that each the time-of-flight (TOF) time corresponds to different light scattering paths resulting in a different phase shift. The phase shift variations produce a speckle pattern, which together with the frequency leakage induced by the discrete Fourier transform (DFT) cause "spikes" in the power spectrum of the beat signal, thus decreasing the accuracy of the measured MTOF values in solid scattering media. For comparison, time-of-flight spectroscopy (TOFS) is also employed to evaluate the MTOF for the same samples, while the geometrical difference between these two techniques is compensated for by using diffusion theory. The MTOFs measured by the FMCW and TOFS techniques agree well, which demonstrates a great potential to develop a robust FMCW setup for simplified MTOF assessment.
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| 7. |
- Mei, Liang, et al.
(författare)
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Combined optical porosimetry and gas absorption spectroscopy in gas-filled porous media using diode-laser-based frequency domain photon migration
- 2012
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Ingår i: Optics Express. - 1094-4087. ; 20:15, s. 16942-16954
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Tidskriftsartikel (refereegranskat)abstract
- A combination method of frequency domain photon migration (FDPM) and gas in scattering media absorption spectroscopy (GASMAS) is used for assessment of the mean optical path length (MOPL) and the gas absorption in gas-filled porous media, respectively. Polystyrene (PS) foams, with extremely high physical porosity, are utilized as sample materials for proof-of-principle demonstration. The optical porosity, defined as the ratio between the path length through the pores and the path length through the medium, is evaluated in PS foam and found consistent with the measured physical porosity. The method was also utilized for the study of balsa and spruce wood samples.
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| 8. |
- Mei, Liang, et al.
(författare)
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Differential absorption lidar system employed for background atomic mercury vertical profiling in South China
- 2014
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Ingår i: Optics and Lasers in Engineering. - : Elsevier BV. - 0143-8166. ; 55, s. 128-135
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Tidskriftsartikel (refereegranskat)abstract
- A differential absorption lidar (DIAL) system based on a Nd:YAG laser pumped narrow-band dye laser is developed and employed to monitor the atmospheric background concentration of atomic mercury in Guangzhou, South China. Atmospheric oxygen is also studied by using neighboring wavelengths to the mercury absorption line (253.7 nm), and is used to verify the operation of the DIAL system. A 24-hour continuous monitoring of background mercury concentration is performed and the average atomic mercury concentration below 330 m is between 5 ng/m(3) and 12 ng/m(3). (C) 2013 Elsevier Ltd. All rights reserved.
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| 9. |
- Mei, Liang, et al.
(författare)
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First attempt to monitor atmospheric glyoxal using differential absorption lidar
- 2012
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Ingår i: Proceedings of the SPIE. - : SPIE. ; 853412
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Konferensbidrag (refereegranskat)abstract
- Glyoxal (CHOCHO), as an indicator of photochemical “hot spots”, was for the first time the subject of a differential absorption lidar (DIAL) campaign. The strongest absorption line of glyoxal in the blue wavelength region – 455.1 nm – was chosen as the experimental absorption wavelength. In order to handle the effects of absorption cross-section variation of the interfering gas – nitrogen dioxide (NO2) – three-wavelength DIAL measurements simultaneously detecting glyoxal and NO2, were performed. The differential absorption curves, recorded in July 2012, indicate an extremely low glyoxal concentration in Lund, Sweden, although it is expected to be peaking at this time of the year.© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
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| 10. |
- Mei, Liang, et al.
(författare)
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Frequency-modulated light scattering in colloidal suspensions
- 2013
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 102:6, s. 061104-
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Tidskriftsartikel (refereegranskat)abstract
- Frequency-modulated light field fluctuations due to moving particles in colloidal suspensions are examined using heterodyne interferometry. The power spectrum is the combined result of a time-of-flight-related frequency distribution due to light scattering and frequency shifts due to the Doppler effect. An approximation model is developed based on diffusion theory and verified experimentally. The potential for application towards comprehensive diagnosis of both particle dynamics and optical properties of the examined media is discussed.
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