Refractive index matching fluid

To test the influence of a change in the ambient refractive index on the laser spectrum, the CBNL was immersed in a specially designed beaker containing index-matching fluids with different index of refraction. For each fluid, the emitted spectrum is measured (fpump 2.5 mW). 

Index Matching Fluid—A fluid with an index of refraction close to that of glass that reduces reflections caused by refractive-mdex differences. 

Figure 18. Spatial frequency response of a photopolymer (37). The response is measured in terms of the efficiencies of holographic gratings. For the solid curve each efficiency was measured with the sample immersed in an index-matching fluid, so as to eliminate the effects of any modulation of the sample thickness. For the dashed curve the sample was in air. The curves show that for spatial frequencies >100 lines/mm the response of the material is almost entirely a refractive index modulation, while for <100 lines/mm there is little index modulation but there is a substantial thickness modulation.

Kang, J. H., Lee, K.-J., Nam, J. H. et al. 2010. Visuahzation of invasion-percolation drainage process in porous media using density-matched immiscible fluids and refractive-index-matched solid structures. Journal of Power Sources 195 2608-2612. 

Figure 11. Effect of the extra-cellular fluid to cytoplasm refractive index matching on the microscope image of dysentery bacteria cells. There is a sharp enhancement of the membrane brightness. (Ref. 51, p. 70)...

Curvature. As the laser beams travel through curved surfaces, they are deflected due to changes in the refractive index. This produces a lensing effect that moves the measuring volume away from its expected location. The problem can be addressed in two ways by refractive index matching of the fluid with the vessel, or by performing beam tracing calculations to correct for the displacement (see Kresta and Wood, 1993). 

Figure 4.17, the surface is a cylindrical section in elevation and approximately toroidal as viewed from the end. The detector boxes have reflecting surfaces at the inner polygonal surface (approximately in the radiator x - z plane) and at a 60° angle in the same plane to save phototubes. They are filled with a fluid whose refractive index matches that of cpiartz, so there are no reflections at the radiator ( iids or phototulie windows. The device works in the near ultraviolet and the visible. It is thin and compact, robust, very fast, and self triggering if desired. 

Bailey, B. C. and Yoda, M. 2003. An aqueous low-viscosity density- and refractive index-matched suspension system. Exp. Fluids 35,1-3. 

Brewster s law. Reflected light in general is more polarised than the incident light and according to Brewster s law, the polarisation is maximum when i + r = 90 where i and r are the angles of incidence and refraction. There are several methods described in the literature such as those based on the use of prisms and fluid immersion (in fluids of known refractive indices) and index matching. The so-called Becke line technique for index matching uses observations under microscope. 

The scattering chamber consists of the sample holder and the associated optical components. For most work, temperature control of the sample must be included (at least to 0.1°). If only a small amount of the sample is available necessitating use of a small volume scattering cell, the cell should be surrounded with a fluid such as deca-hydronapthalene which matches the index of refraction to that of the scattering cell. In this way the scatter caused from the change in refractive index at the air/glass interface can be substantially removed from the vicinity of the scattering volume. 

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