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Digitale Medien

Phase gratings in the visible and near-infrared spectral range realized by metastable electronic states in $\rm Na_2[Fe(CN)_5NO] \cdot 2H_2O$ (1996)

Woike, T. ; Haussühl, S. ; Sugg, B. ; [weitere]

Springer

Applied physics 63 (1996), S. 243-248

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ISSN: 1432-0649

Schlagwort(e): PACS:42.40.Pa; 42.70.Gi; 42.70.Ln

Quelle: Springer Online Journal Archives 1860-2000

Thema: Physik

Notizen: Abstract. Phase and amplitude gratings in the visible and near-infrared spectral range can be written in SodiumNitroPrusside (SNP), $\rm Na_2[Fe(CN)_5NO] \cdot 2H_2O$ , single crystals by optical excitation of infinitely long-living metastable electronic states, localized in the $\rm [Fe(CN)_5NO]^{2-}$ anions. Hence, its photorefractive effect does not depend on dopants or defects. The refractive index is modulated by more than $\Delta n = 1 \times 10^{-3}$ in the red $(632.8$ nm) and $\Delta n = 5 \times 10^{-4}$ in the near-infrared region $(1047$ nm). The absorption coefficient is modulated by about $\Delta \alpha = 100$ m $^{-1}$ at $632.8$ nm and 40 m $^{-1}$ at 1047 nm. The wavelength dependence of $\Delta n$ can be explained by strong absorption bands in the ultraviolet considering Kramers-Kronig dispersive analysis. The time constant of the write-read-erase processes and the diffraction efficiency $\eta$ depend on light intensity, wavelength and polarization of the light with respect to the crystallographic axes. After excitation of the metastable states the indicatrix is modulated only along the $a$ - and $b$ -axis of the orthorhombic system.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF01833793

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Digitale Medien

Electrophoresis versus electrochromatography (1989)

Everaerts, F. M. ; van de Goor, A. A. A. M. ; Verheggen, Th. P. E. M. ; [weitere]

Weinheim : Wiley-Blackwell

Journal of High Resolution Chromatography 12 (1989), S. 28-31

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ISSN: 0935-6304

Schlagwort(e): Electrophoresis ; Electrochromatography ; Capillary zone electrophoresis (CZE) ; Electroosmosis ; Chemistry ; Analytical Chemistry and Spectroscopy

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Chemie und Pharmazie

Notizen: In separation techniques, such as Liquid Chromatography and Capillary Zone Electrophoresis, separation is performed on the basis of differences in velocity of the various separands, making use of differences in k′ and/or effective mobility.While in chromatography the flow of the eluent is elementary, in electrophoretic techniques the electroosmotic flow is generally suppressed in order to avoid disturbing of the sample zone boundaries, which migrate with a maximal velocity of 10-3 m s-1. This holds especially for isotachophoretic separations, where separands migrate in consecutive zones with minimal detectable lengths of about 0.1 mm.If electroosmotic flow is applied as a transport mechanism, using capillaries as small as about 50 μm, linear velocities of the liquid flow can reach about 2 × 10-3 m s-1. Especially for ionic species with a low effective mobility, this velocity can be a multiple of the electrophoretic migration velocity in the separation compartment. Therefore, anionic, non-ionic, and cationic separands can migrate in the same direction.Depending on whether repulsive or attractive forces are operative, the electrophoretic separation power can be counteracted or favored. The separation mechanisms making use of (quasi)stationary phases are studied.Plotting the chromatographic behavior versus the electrophoretic shows transition areas to exist between the “purely” electrophoretic techniques and the “purely” chromatographic techniques.It must be stated that most of the recent publications in CZE, especially those with very narrow bore capillaries, can be allocated to the transition areas, sometimes with a strong chromatographic retention component.

Zusätzliches Material: 4 Ill.