Two-prism method

Figure 10. The two prism method for surface electromagnetic wave spectroscopy as developed by Schoenwaid, Burstein, and Elson (14)...

The optical propagation losses in the vacuum evaporated benzylic amide [2] catenane thin films, measured in planar waveguide configuration [47, 48] were found to be PL = 2.8 0.1 dB/cm at A = 1.32 (xm and PL = 4.0 0.1 dB/cm at A = 1.55 (xm, respectively. These values were determined by a two prism method [49]. As for polycrystalline thin films these value are significantly smaller han usually observed. It shows the ability of these molecules to form good optical quality thin films by using these technologically friendly technique. It shows also that the crystallites are very small, tens to a few hundreds of nanometers size. 

The basic method is to use a manual Abbe refractometer to determine refractive index. Various automated or electronic instruments exist which automatically perform some of the steps of the manual procedure. The first requirement is that the sample be a solution. In some instruments, the solution is placed between two prisms, and the image of the critical ray boundary is adjusted to meet a reference mark for this adjustment, the refractive index and equivalent °Brix can be read from a scale. The sample temperature must be known, or the instrument must have temperature compensation. Some automatic digital refractometers use the same methodology of sample presentation, but automate the matching of the critical boundary to the reference marker. 

The single prism technique has the advantage that ordinary sources with a monochromator can be used. The two prism technique requires an extremely well collimated beam, and only lasers are satisfactory as sources. However, the two prism technique is more sensitive to absorption in the thin film. We shall give some examples of data obtained using each method. It must be admitted that much of the wdrk to date has been of an exploratory nature, designed to demonstrate the utility of spectroscopy using surface waves. 

Using the standard method, introduce the sample to be measured between the two prisms. If it is a free-flowing liquid, it may be introduced into a channel along the side of the prisms, injected from a Pasteur pipette. If it is a viscous sample, the prisms must be opened (they are hinged) by lifting the upper one a few drops of liquid are applied to the lower prism with a Pasteur pipette or a wooden applicator. If a Pasteur pipette is used, take care not to touch the prisms because they become scratched easily. When the prisms are closed, the liquid should spread evenly to... 

Prediction of the precise pitches for phase matching requires the measurement of and a [see Eqs. (26) and (6). Since is an average over the two principal dielectric constants in the ordered phase, we measured c(cu) and (3cu) with X = 1.06 Mm in the isotropic liquid phase where the random orientations of the molecules gives the desired average. It was assumed that the small variation of r due to temperature and phases could be neglected. We used the prism method with a mercury-arc lamp as the light source and a filtered photomultiplier tube as the detector. The results are given in Table II. 

In Abbe s double prism method a thin ho-meotropically oriented nematic film is placed between the hypotenuse faces of two rectangular prisms. Using light polarized parallel and perpendicular to the optical axis, respectively, the principal refractive indices and can be obtained directly from the critical angle of total reflection, provided that the refractive index of the prism is greater than that of the liquid crystal [2, 8-10]. In some cases the director of the nematic phase was oriented uniformly parallel to the prism planes [11-14]. Special variants of the total reflection method have been described [3, 4, 15, 16]. A total reflection refractometer of the Abbe type has also been used to determine n, n and An in the infrared region between 2.5 and 14 p.m [17]. 

This method is used to determine sodium and potassium in food, water and blood serum. The flame can be hydrogen/oxygen, methane/ oxygen or methane/air fueled. Wavelength selection can be by filter, prism Fig. 9.2 or grating and by either one or two detectors. 

Figure 5. SPR sensor based on ATR method and angular modulations (upper) and corresponding reflectivity calculated for two different refractive indices of sample (lower). Sensor configuration SF14 glass prism, 50 nm thick gold layer, sample, wavelength - 682 nm.

The EPA Method 2 probe uses a standard S-type Pitot tube to determine the velocity pressure by measuring gas flow as a unidirectional vector. This method is typically 10-20% higher than the calculated flue gas rate from the FCC heat balance. The newly develop EPA Method 2F probe is a five-holed prism tip with a thermocouple. A centrally located tap measures the stagnation pressure, while two lateral taps measure the static pressure. The yaw angle is determined by rotating the probe until the difference between the two lateral holes is zero. This method closely matches the... 

Many elements are present in the earth s crust in such minute amounts that they could never have been discovered by ordinary methods of mineral analysis. In 1859, however, Kirchhoff and Bunsen invented the spectroscope, an optical instrument consisting of a collimator, or metal tube fitted at one end with a lens and closed at the other except for a slit, at the focus of the lens, to admit light from the incandescent substance to be examined, a turntable containing a prism mounted to receive and separate the parallel rays from the lens and a telescope to observe the spectrum produced by the prism. With this instrument they soon discovered two new metals, cesium and rubidium, which they classified with sodium and potassium, which had been previously discovered by Davy, and lithium, which was added to the list of elements by Arfwedson. The spectroscopic discovery of thallium by Sir William Crookes and its prompt confirmation by C.-A. Lamy soon followed. In 1863 F. Reich and H. T. Richter of the Freiberg School of Mines discovered a very rare element in zmc blende, and named it indium because of its brilliant line in the indigo region of the spectrum. 

The limit of concentration attainable by any of the foregoing methods is about 98 per cent. If acid of higher concentration than this is required, acid of 97 to 98 per cent, strength can be partially frozen,2 when the colourless prisms which separate contain 99-5 to 100 per cent. H2S04 and constitute the frequently so-called, but misnamed, monohydrate. Owing to the success of the contact process for the preparation of sulphur trioxide and of fuming sulphuric acid, the production of highly concentrated sulphuric acid has been rendered so simple a matter that concentration of the lead chamber acid is of diminished importance. The main value of the chamber process lies in its economical production of a not necessarily very concentrated acid. There are indications, however, that by a suitable combination of the two processes, an even more economical production of concentrated acid may be obtainable (see p. 162). 

---