Prism refraction

Figure 4. Reflectivity in the Kretschmarm geometry of ATR consisting of an SF14 glass prism (refractive index - 1.65), a gold layer (thickness - 50 nm), and a low refractive index dielectric medium (refractive index - 1.32), and wavelength - 800 nm.

For SPR-measurements, two layers with a thickness of less than 100 nm were prepared on BK7-prisms (refractive index d = 1.51680, Krombach, Germany) and all other layers were prepared on NPH2-prisms ( d = 1.92286, Ohara, Japan) to fulfil the resonance conditions of the surface plasmons. To prepare layers for the RlfS-measurements, the solutions were spin-coated onto glass-substrates with a Ta205-layer for reflection enhancement. Si-wafers were used for the ellipsometric measurements. 

Light from a slit is collimated by a lens and passed into a prism. Since the prism refracts the light of different frequencies by different amounts, a beam of white light, for example, is spread out into its component frequencies (colors). These different frequencies appear at different positions on the receptor. Typically a detector such as a photoelectric tube can be moved across the receptor area to measure the intensity of light of each frequency. The receptor is marked with a scale of wavelengths or frequency. 

The physics of X-ray refraction are analogous to the well known refraction of light by optical lenses and prisms, governed by Snell s law. The special feature is the deflection at very small angles of few minutes of arc, as the refractive index of X-rays in matter is nearly one. Due to the density differences at inner surfaces most of the incident X-rays are deflected [1]. As the scattered intensity of refraction is proportional to the specific surface of a sample, a reference standard gives a quantitative measure for analytical determinations. 

The real utility of d comes in the analysis of thin films. Consider a substrate of refractive index supporting a thin film of thickness d and refractive index in contact with an internal reflection element (the prism) of refractive index as shown in Figure 24. In this case, d depends on the polarization of the incident light beam and is given by... 

The method of measurement is based upon the observation of the position of the border line of the total reflection in relation to the faces of a prism of flint-glass, into which the light from the substance under in vestigation enters by the action of refraction. 

The double prism consists of two similar prisms of flint-glass, each cemented into a metal mount and having a refractive index n, = 1 75 the fluid to be investigated (a few drops) is deposited between the two adjoining inner faces of the prisms in the form of a thin stratum (about 0 15 mm. thick). The former of the two prisms, that farther from the ttelescope (which can be folded up or be removed), serves solely for the purpose of illumination, while the bordw line is formed in the second flint prism. 

The border line is now adjusted upon the point of intersection of the crossed lines by slightly inclining the double prism to the telescope by means of the alidade. The position of the pointer on the graduation of the sector is then read off by the aid of the magnifier attached to the alidade. The reading supplies the refractive index itj of the substance under investigation itself, without any calculation. 

As the refractive index of fluids varies with the temperature, it is of importance to know the temperature of the fluid contained in the double prism during the process of measurement. 

In the laboratory, RI is measured using a refractometer. The instrument has two prisms and a light source. The technician spreads a small amount of sample on the faces of both prisms in the refractometer. The light is then directed at the sample and the scale is read. The observed scale is then converted to a refractive index with tables supplied with the instrument and corrected for the sample temperaturi. ... 

The deflection refractometer (Fig. 8.4), which measures the deflection of a beam of monochromatic light by a double prism in which the reference and sample cells are separated by a diagonal glass divide. When both cells contain solvent of the same composition, no deflection of the light beam occurs if, however, the composition of the column mobile phase is changed because of the presence of a solute, then the altered refractive index causes the beam to be deflected. The magnitude of this deflection is dependent on the concentration of the solute in the mobile phase. 

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