| 1. |
- Auzel, Francois
(författare)
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A condition in Ln-doped materials for flat optical gain
- 2007
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Ingår i: Spectroscopy Letters. - : Informa UK Limited. - 0038-7010 .- 1532-2289. ; 40:2, s. 197-207
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Tidskriftsartikel (refereegranskat)abstract
- Fundamental conditions that rule gain flatness in Er-doped glass optical amplifiers are investigated using few parameters obtained by drastic simplifications for level positions and widths. The obtained general gain flatness condition for rare-earth-doped glasses contains two parts: a general one valid in any material and a slight modulation of it valid only for glasses when "0-0" transitions are involved. Essentially, the electron-phonon coupling for the considered materials has to be larger than 2/3. In order to exemplify these conditions, they are calculated for fluoride and silicate glasses, which are known to display respectively flat and non-flat gain behavior.
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| 2. |
- Davidsson, A., et al.
(författare)
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Electric Dichroism Spectroscopy
- 1977
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Ingår i: Spectroscopy Letters. - : Informa UK Limited. - 1532-2289 .- 0038-7010. ; 10:6, s. 447-454
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Tidskriftsartikel (refereegranskat)abstract
- Legrand-Grosjean circular dichroism spectrometers are easily converted to detect electric dichroism (ELD), i.e. anisotropic absorption due to an external electric field. The sensitivity enables the studying of small molecules with dipole moments or anisotropic polarisabilities. The observed ELD is in part due to the orientation of the absorbing transition dipole (the orientational distribution being given by the interaction between the dipole and the electric field) but contributions due to perturbations (type Stark) may generally not be neglected. The method is predicted to become an important complement to LD studies in oriented matrix, to evaluate directions of transitions moments, but other applications are also possible. The experimental qualifications are demonstrated on two different species, nitrobenzene and Cu(II) ethylenediamine (acetylacetone)2.
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| 3. |
- Davidsson, A., et al.
(författare)
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Linear Dichroism of 1,4-Benzodiazepines
- 1976
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Ingår i: Spectroscopy Letters. - : Informa UK Limited. - 1532-2289 .- 0038-7010. ; 9:5, s. 301-311
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Tidskriftsartikel (refereegranskat)abstract
- Linear dichroism and absorption spectra were measured for some 1,4-benzodiazepines dissolved and partially oriented in a polymer matrix. The results are discussed in terms of polarizations of the transitions in the two noninteracting benzene nuclei.
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| 4. |
- Jonas, I., et al.
(författare)
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Orientation Studies of Probe Molecules in Lamellar Liquid Crystalline Lipid Systems by Linear Dichroism
- 1977
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Ingår i: Spectroscopy Letters. - : Informa UK Limited. - 1532-2289 .- 0038-7010. ; 10:6, s. 501-506
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Tidskriftsartikel (refereegranskat)abstract
- The LD-method of inclined incidence was found useful in the study of the orientations of probe chromophores (carotene, anthracene) solubilized in lamellar mesophases of the systems sodium octanoate/decanol/water and sodium di-2-ethylhexylsulphosuccinate/water, respectively. The results suggest the existence of two competing molecular orientation mechanisms aligning the longest axis of the probe molecule either parallel with the lamellar surface or perpendicular to it.
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| 5. |
- Kristensson, Elias, et al.
(författare)
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Improved spectral sensitivity by combining periodic shadowing and high dynamic range imaging
- 2016
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Ingår i: Spectroscopy Letters. - : Informa UK Limited. - 0038-7010 .- 1532-2289. ; 49:2, s. 91-95
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Tidskriftsartikel (refereegranskat)abstract
- Most emission spectra are characterized by lines of various intensities, a feature making them difficult to probe in their entirety - the limited dynamic range of the detector prohibits the simultaneous observation of both weak and intense spectral features. A further known complication in spectroscopy concerns the generation and detection of stray light, which is an undesired contribution of light, often associated with unavoidable imperfections in the spectrometer. Stray light leads to an offset that often exceeds the intensity of weak lines, especially those that were barely detectable in the absence of stray light. This problem is well-known in, for example, laser-induced Raman spectroscopic measurements. In this paper, we describe a methodology to solve both the stray light problem and that associated with the limited dynamic range of the detector. The method is based on combining the high dynamic range imaging concept commonly employed in digital photography with the periodic shadowing technique, where the former is used to boost the dynamics and the latter to suppress stray light. The capabilities of the approach, which is suitable for investigation of temporally stable sources, are demonstrated and the results are compared with measurements performed with both conventional equipment and the periodic shadowing technique.
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| 6. |
- Lindkvist, Markus, et al.
(författare)
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Absolute quantifications of oxy- and deoxyhemoglobin concentrations by combination of differentially resolved spectroscopy and spatially resolved spectroscopy
- 2015
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Ingår i: Spectroscopy Letters. - : Taylor & Francis. - 0038-7010 .- 1532-2289. ; 48:3, s. 170-172
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Tidskriftsartikel (refereegranskat)abstract
- This letter proposes a theoretical framework to calculate absolute concentrations of oxy- and deoxyhemoglobin using continuous-wave near-infrared spectroscopy. While previous methods on this topic require assumptions on constant blood volume, the proposed method does not. Equations for the absolute concentrations were derived from a combination of the modified Beer-Lambert equation and the theory of diffusion of photons in turbid media. The method has an advantage over and is theoretically consistent with previous methods. It needs yet to be evaluated in an experimental study.
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| 7. |
- Lindkvist, Markus, et al.
(författare)
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Coherent Derivation of Equations for Differential Spectroscopy and Spatially Resolved Spectroscopy : An undergraduate tutorial
- 2013
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Ingår i: Spectroscopy Letters. - : Taylor & Francis. - 0038-7010 .- 1532-2289. ; 46:4, s. 243-249
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Tidskriftsartikel (refereegranskat)abstract
- Near-infrared spectroscopy (NIRS) is a spectroscopic method that is frequently used in health care and sports medicine to monitor oxygenation parameters in biological tissue. This tutorial provides a coherent derivation of equations for differential spectroscopy and spatially resolved spectroscopy, from basic theories to implementable equations. The basic theories are applicable to any kind of tissue oximeter but mainly focus on continuous-wave instruments.
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| 8. |
- Nordén, Bengt, 1945
(författare)
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Absorption Statistics in Linear Dichroism
- 1977
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Ingår i: Spectroscopy Letters. - : Informa UK Limited. - 1532-2289 .- 0038-7010. ; 10:6, s. 483-488
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Tidskriftsartikel (refereegranskat)abstract
- Attention is called to an artifact in linear dichroism (LD), so called absorption statistics, which leads to reduced LD intensity in regions of high absorption. The reduction factor is larger than that governing the corresponding reduction in absorption, when LD is measured by using a Legrand-Grosjean circular dichroism spectrophotometer. In the case of infinite fibres at perfect order it coincides with the absorption statistical reduction factor of optical activity. The artifact was observed for β-carothene solubilized in lecithin liposomes oriented at flow.
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| 9. |
- Nordén, Bengt, 1945
(författare)
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Field Effects in Condensed Media on Polarized Absorption
- 1977
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Ingår i: Spectroscopy Letters. - : Informa UK Limited. - 1532-2289 .- 0038-7010. ; 10:6, s. 455-470
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Tidskriftsartikel (refereegranskat)abstract
- The existence of anisotropic local field perturbation on electronic absorption is proved by non-zero linear dichroism of isotropic chromophores (Mo(CO)6) in anisotropic environment. Two sources of such effects are possible: a) perturbation of the electronic energy levels in the chromophore by the static electric solvent field (= Stark effect) or, in case of anisotropic polarizable or dipolar molecules, similar effects involving molecular orientation, and b) dielectric effects on the effective radiation field. The latter effect was considered by various models: The Lorentz field model predicts an effect with wrong sign, it also yields too large a magitude if the anisotropy of the field is considered. If no local field correction is made and the anisotropy only operates in the radiation intensity a result more in agreement with experiment is obtained. By using the Onsager-Böttcher model one may take into account specific properties of the absorbing molecule, like anisotropy in α/r3 where α is its polarizability and r its Onsager radius.
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| 10. |
- Nordén, Bengt, 1945
(författare)
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General Aspects on Linear Dichroism Spectroscopy and its Application
- 1977
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Ingår i: Spectroscopy Letters. - : Informa UK Limited. - 1532-2289 .- 0038-7010. ; 10:6, s. 381-400
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Tidskriftsartikel (refereegranskat)abstract
- A possible applicatory scope of linear dichroism in solution chemistry is outlined together with some recent measuring and interpretation methods. The possibility to obtain structural information is stressed. The applications are illustrated by experimental results.
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