| 1. |
- Chen, Guanying, et al.
(författare)
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Near vacuum ultraviolet luminescence of Gd3+ and Er3+ ions generated by super saturation upconversion processes
- 2009
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Ingår i: Optics Express. - 1094-4087. ; 17:19, s. 16366-16371
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Tidskriftsartikel (refereegranskat)abstract
- Near vacuum ultraviolet (UV) upconversion (UC) emissions with a spectral resolution of 1 nm, from the (6)G(J), D-6(J), I-6(J), P-6(J) levels of Gd3+ and the L-2(17/2), D-4(7/2), H-2(2)(9/2), D-2(5/2), (4)G(7/2), K-2(13/2), P-2(3/2) levels of Er3+, were observed under 974 nm laser excitation. Mechanism analyses illustrate that successive energy transfers (ETs) from Yb3+ to Er3+ generate UV UC radiations in Er3+, while two resonant ETs from Er3+ to Gd3+ lead to UV UC radiations in Gd3+. Power dependence analyses indicate that the expected inefficient four- and five-photon processes have been switched into efficient two-photon processes due to a super saturation UC phenomenon that employs consecutive saturations at the intermediate states. (C) 2009 Optical Society of America
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| 2. |
- Grönlund, Rasmus, et al.
(författare)
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Remote LIBS and Raman imaging for assessment of cultural heritage
- 2005
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Ingår i: 2005 Conference on Lasers and Electro-Optics Europe. - 0780389743 ; , s. 684-684
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Konferensbidrag (refereegranskat)abstract
- In this paper, we propose to perform remote laser-induced breakdown spectroscopy (LIBS) and Raman imaging of historical monuments to assess the state of a building. The lidar system is equipped with a Nd:YAG pumped optical parametrical oscillator (OPO) system, allowing laser radiation in the wavelength range 220 nm-4 μm. The laser radiation can be sent through a roof-top dome which can steer the radiation onto the point of interest
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| 3. |
- Lou, Xiutao, et al.
(författare)
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Gas detection by correlation spectroscopy employing a multimode diode laser
- 2008
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Ingår i: Applied Optics. - 2155-3165. ; 47:13, s. 2392-2398
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Tidskriftsartikel (refereegranskat)abstract
- A gas sensor based on the gas-correlation technique has been developed using a multimode diode laser (MDL) in a dual-beam detection scheme. Measurement of CO2 mixed with CO as an interfering gas is successfully demonstrated using a 1570 run tunable MDL. Despite overlapping absorption spectra and occasional mode hops, the interfering signals can be effectively excluded by a statistical procedure including correlation analysis and outlier identification. The gas concentration is retrieved from several pair-correlated signals by a linear-regression scheme, yielding a reliable and accurate measurement. This demonstrates the utility of the unsophisticated MDLs as novel light sources for gas detection applications.
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| 4. |
- Lou, Xiutao, et al.
(författare)
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Oxygen measurement by multimode diode lasers employing gas correlation spectroscopy
- 2009
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Ingår i: Applied Optics. - 2155-3165. ; 48:5, s. 990-997
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Tidskriftsartikel (refereegranskat)abstract
- Multimode diode laser (MDL)-based correlation spectroscopy (COSPEC) was used to measure oxygen in ambient air, thereby employing a diode laser (DL) having an emission spectrum that overlaps the oxygen absorption lines of the A band. A sensitivity of 700 ppm m was achieved with good accuracy (2%) and linearity (R-2 = 0.999). For comparison, measurements of ambient oxygen were also performed by tunable DL absorption spectroscopy (TDLAS) technique employing a vertical cavity surface emitting laser. We demonstrate that, despite slightly degraded sensitivity, the MDL-based COSPEC-based oxygen sensor has the advantages of high stability, low cost, ease-of-use, and relaxed requirements in component selection and instrument buildup compared with the TDLAS-based instrument. (C) 2009 Optical Society of America
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| 5. |
- Lou, X. T., et al.
(författare)
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Gas sensing by tunable multimode diode laser using correlation spectroscopy
- 2008
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Ingår i: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 93:2-3, s. 671-676
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Tidskriftsartikel (refereegranskat)abstract
- A novel method to use multimode diode lasers for gas detection is demonstrated. The relationship between the intensity decay of partially absorbed multiple modes and the target gas concentration is presented. The gas concentration is retrieved by a linear-regression-based procedure applied on simultaneously recorded absorption signals in a dual-beam wavelength-modulation configuration. Signals of non-gas origin or disturbed by interfering gases are effectively eliminated by correlation analysis procedure. Light intensity fluctuations and wavelength shifts due to temperature drift are automatically compensated for. Several absorption signals can readily be obtained within a limited tuning range by overlapping the laser multimode chart with the target gas spectrum. This scheme was applied on the detection of trace acetylene mixed in ambient air, and a sensitivity of 3 ppm was achieved with a 48.5 cm path length. The trade-off between sensitivity and reliability for retrieving gas concentration by multiple absorption signals is also presented.
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| 6. |
- Lou, X. T., et al.
(författare)
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Sulfur dioxide measurements using an ultraviolet light-emitting diode in combination with gas correlation techniques
- 2009
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Ingår i: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 94:4, s. 699-704
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Tidskriftsartikel (refereegranskat)abstract
- The important air pollutant sulfur dioxide has a strong structured absorption band in the ultraviolet (UV) region around 300 nm. Recently, light-emitting diodes (LEDs) with structureless emission in a band about 15-nm wide in the UV region have become available. We demonstrate that they can be ideal sources for gas absorption measurements combined with the gas correlation technique, where an absorption cell with an optically thick column of the gas under investigation is used for analysing the target gas contents in a path between the LED and the measurement device. A sensitivity of 0.4 ppm sulfur dioxide was obtained with a 19-cm optical path length and 60-s integration time. Particularly compact and cost-effective monitors especially for industrial emissions can be envisaged.
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| 7. |
- Sjöholm, Mikael, et al.
(författare)
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All-diode-laser ultra-violet absorption spectroscopy and temporal gas correlation spectroscopy
- 2005
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Ingår i: 2005 Conference on Lasers and Electro-Optics Europe. - 0780389743 ; , s. 443-443
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Konferensbidrag (refereegranskat)abstract
- Here, we present a scheme producing UV radiation around 302 nm by sum-frequency generation in beta-barium borate employing a blue and a near-infrared diode laser. The diode-laser-based spectrometer has a mode-hop-free tuning range of 50 GHz and can be used for high-resolution spectroscopic detection of sulfur dioxide. Differential measurements of several sulfur dioxide gas concentrations, at low pressure as well as at ambient atmospheric pressure, are demonstrated. A particularly interesting aspect of the mixing scheme, is that the near-infrared and blue radiation can be tuned to absorption features of water and nitrogen dioxide, respectively
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| 8. |
- Somesfalean, Gabriel, et al.
(författare)
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All-diode-laser ultraviolet absorption spectroscopy for sulfur dioxide detection
- 2005
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Ingår i: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 80:8, s. 1021-1025
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Tidskriftsartikel (refereegranskat)abstract
- Ultraviolet radiation around 302 nm was produced by sum-frequency generation in beta-barium borate employing a blue and a near-infrared diode laser. The diode-laser-based spectrometer has a mode-hop-free tuning range of 50 GHz and was used for high-resolution spectroscopic detection of sulfur dioxide. Differential measurements of several gas concentrations, at low pressure as well as at ambient atmospheric pressure, were demonstrated. The detection limit in the first implementation of the instrument was about 20 ppm m at atmospheric pressure, essentially limited by interference fringes. Methods for greatly improving this limit are suggested.
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| 9. |
- Somesfalean, Gabriel, et al.
(författare)
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Long-path monitoring of NO2 with a 635 nm diode laser using frequency-modulation spectroscopy
- 2005
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Ingår i: Applied Optics. - 2155-3165. ; 44:24, s. 5148-5151
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Tidskriftsartikel (refereegranskat)abstract
- In situ monitoring of traffic-generated nitrogen dioxide (NO2) emissions using long-path absorption spectroscopy is reported. High-sensitivity detection of NO2 is achieved by employing two-tone frequencymodulation spectroscopy at a visible absorption band using a tunable high-power diode laser operated around 635 nm. A real-time absorption spectrometer is accomplished by repetitively applying a rectangular current pulse to the diode-laser operating current, allowing detection of isolated NO2 absorption lines. A detection limit of 10 mu g/m(3) for NO2 at atmospheric pressure using a 160 m absorption path is demonstrated. Continuous monitoring of NO2 over a road intersection at peak traffic is performed.
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| 10. |
- Somesfalean, Gabriel, et al.
(författare)
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Temporal correlation scheme for spectroscopic gas analysis using multimode diode lasers
- 2005
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 86:18
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Tidskriftsartikel (refereegranskat)abstract
- The reliability of diode lasers used in spectroscopic applications is limited by their intrinsic multimode and mode-jump behavior when wavelength-tuned by current or temperature. We report on a scheme for gas analysis based on temporal correlation between absorption signals from an unknown external and a known reference gas concentration, simultaneously recorded when the diode laser wavelength is temperature-tuned across absorption features of the gas of interest. This procedure, which does not require any knowledge of the exact spectrum, also eliminates light intensity fluctuations due to mode competition. The method is illustrated for atmospheric oxygen absorption applied to diffusion measurements.
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