Immersion oils 258 INDEX

The prism and shde may be optically coupled with glycerol, cyclohexanol, or microscope immersion oil, among other liquids. Immersion oil has a higher refractive index (thereby avoiding possible TIR at the prism/coupling liquid interface at low incidence angles), but it tends to be more autofluorescent (even the extremely low fluorescence types). 

Prior to measurement of reflectance, the sample face is covered with cedar oil or commercial immersion oil and then multiple readings are taken of the maximum reflectance of the coal component (e.g., vitrinite) of interest. These values are compared with readings of high-index glass standards (of known reflectance) that are available with reflectance values typically ranging from 0.302 to 1.815%. 

Figure 35. Fluorescence lifetime versus peak emission wavelength /p for car-bocyanine dye molecules spin coated on a PMMA surface. In (a), the sample was overcoated with several micrometers of PMMA (crosses) or refractive index matching immersion oil (circles). The solid line is a fit of the radiative lifetime, Trad, to the upper bound of the data points. In (B) the molecules are at the PMMA-air interface the solid lines are calculated lifetimes for different polar orientations 6t of the emission dipoles and nonradiative decay rates l/tnr. (Adopted from [115].)...

USE Immersion fluid in the determination of the refractive index nf crystals. For the determination of water in ale by the cloud point method. For refractometric fat determinations. Mixed with polymerized castor oil as a genera] immersion oil in microscopy. 

To observe the dynamics of small structures such as the growth of single actin filaments in solution or on functionalized beads, a specialized TIRF microscope is needed. Critical for TIRF imaging are furthermore a sensitive CCD Camera, high-quality objectives with a high numeric aperture (NA > 1.4), immersion oil (e.g., Leica with a refractive index of 1.518) as well as suitable lasers and filter sets. These days, complete systems for TIRF microscopy can be purchased from manufacturers such as Olympus, Nikon or Leica. 

Unless otherwise marked, objective lenses require no immersion medium. Immersion media improve the NA of the lens, specifically allowing values >1 to be achieved. Immersion lenses are usually optimized for one particular immersion medium (immersion oil [oil, oel, H.I.], glycerol or glycerin, or water [W.I., WAS]), a drop of which is place between the objective front lens and the cover-slip. Some objectives have a rotating collar, which compensates for the refractive index of different media (air = 1.00, water = 1.33, glycffol = 1.47, oil = 1.52). 

Numerical aperture n. The numerical aperture of a lens system (objective or condenser) is the sine of one-half the angular aperture times the refractive index of the medium (1.0 for air, 1.515 for Cargille immersion oil, etc.) between objective and specimen. The numerical aperture is a measure of the light gathering capacity of the lens system and determines its resolving power and depth of field. 

Figure 3.18 (a) The numerical aperture of an objective is defined in terms of the half angle of the cone of rays (/ii).The effect of using an immersion oil is shown in (b) and (c)—peripheral rays which are refracted out of the cone defined by the numerical aperture when the space between the coverglass and objective is filled with air, propagate into the front lens of the objective when refraction is eliminated by filling the space with index matching oil. 

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