Multiple beam interferometer

To simplify FECO evaluation, it is conmion practice to experimentally filter out one of the components by the use of a linear polarizer after the interferometer. Mica bireftingence can, however, be useftil to study thin films of birefringent molecules [49] between the surfaces. Rabinowitz [53] has presented an eigenvalue analysis of birefringence in the multiple beam interferometer. 

In a grating spectrometer, the interfering partial waves emitted from the different grooves of the grating all have the same amplitude. In contrast, in multiple-beam interferometers these partial waves are produced by multiple reflection at plane or curved surfaces and their amplitude decreases with increasing number of reflections. The resultant total intensity therefore differs from (4.25). 

Fig. 4.37. Transmittance of an absorption-free multiple-beam interferometer as a function of the phase difference 0 for different values of the finesse F ...

As a consequence of these characteristics, SPR is ideally suited to probe a few nanometres from the metal surface, a distance well below the wavelength of the light used to generate the plasmons. In essence, the surface plasmon technique can be likened to a multiple-beam interferometer, with one narrow... 

The thicknesses of the films on the sapphire substrates were measured with a multiple-beam interferometer and ranged from 442 to 4740 A. In the case of the films deposited on tantalum, the film thickness could not be measured optically because of the rough surface of the tantalum substrate. The thickness of boron films on tantalum subsfrates was estimated from the measured X-ray fluorescence of boron deposited using electron probe microanalysis (EPMA) with a 7-kV acceleration voltage, a 0.1-pA sample current, and a 100-pm beam diameter. The relation between the X-ray intensity and the film thickness was previously obtained using boron films on a sapphire substrate. 

The diffraction grating monochromator is a specific example of mnltiple beam interference effects. Interference between multiple beams can be generated by both division of amplitude (as in the Fabry-Perot interferometer) or by division of wave front (as in the diffraction grating). (Figures 5.9 and 5.10)... 

Examples of devices in which only two partial beams interfere are the Michelson interferometer and the Mach-Zehnder interferometer. Multiple-beam interference is used, for instance, in the grating spectrometer, the Fabry-Perot interferometer, and in multilayer dielectric coatings of highly reflecting mirrors. 

Several types of atom interferometers have been realized that use various light-field configurations to split and recombine atomic beams. The main requirement for the light field is that it should split the atomic wave by the maximum possible angle without multiple scattering of the beam. So far, researchers have failed to devise an ideal laser atomic-beam splitter that would be comparable with the semitransparent mirrors in optical interferometry. 

An example of a Martin-Puplett interferometer is schematically illustrated in Figure 19.1. The important characteristic of the Martin-Puplett interferometer lies in its use of a wire-grid polarizer (WGP) as the beamsplitter this is free from the effects of interference arising from multiple internal reflections occurring inside a PET film. The WGP used for the Martin-Puplett interferometer is an array of parallel metallic wires, each having a diameter of about 10 pm and separated by intervals of about 12.5 pm. A beam of far-infrared radiation incident on the WGP is divided into two orthogonal polarized components that is, a component with its plane of polarization parallel to the wires, which is reflected, and a component with its plane of polarization perpendicular to the wires, which is transmitted. Thus, the WGP performs the role of a beamsplitter. 

The most common sample compartment in high-resolution FT-IR spectrometers is the White cell, where the beam passes a path of 1-1000 m. In a long-path gas cell, however, a small f/number (focal length of the mirror/diameter of the pupil) and a large size of the circular image may lead to a loss of effectivity. In the Oulu interferometer this problem was solved by an alternative multiple-path gas cell, where the images at the focal planes occur on a circle around the principal axis of the cell. The aberrations remain small in spite of a small f/number, because the successive images are relatively near to the principal axis of the optics. 

---