Fixed plane mirror

A commercial high-resolution FTS is depicted in Fig. 4.2. The output of the broadband source is focused on a circular aperture (entrance iris). As in the dispersive set-up, the optical beam is made parallel by a collimating mirror, and it intercepts a beam splitter at a non-normal incidence (usually 45 or 60°). One part of the beam is transmitted towards a fixed plane mirror while the other part towards a plane mirror, which can be translated continuously or in steps at a given distance (scan mirror). The beams reflected back by... 

A diagram of a typical interferometer (Michelson type) is shown in Figure 7.8. It consists of fixed and moving front-surface plane mirrors (A and B) and a beamsplitter. Collimated infrared radiation from the source incident on the beamsplitter is divided into two beams of equal intensity that pass to the fixed and moving mirrors respectively. Each is reflected back on itself, recombining at the beamsplitter from where they are directed through the sample compartment and onto the detector. Small... 

The Michelson interferometer consists simply of two mutually perpendicular plane mirrors one of which is fixed and the other able to move at 90° to its plane. A semi-reflecting film or beamsplitter ... 

The Michelson interferometer is shown schematically in Figure 1. It consists of two mutually perpendicular plane mirrors, one of which can move at a constant rate along the axis and one of which is stationary. Between the fixed mirror and the movable mirror is a beam splitter where a beam of radiation from an external source can be partially... 

The interferometer consists of two plane mirrors, one fixed and the other moving, and a beam splitter. The light comes parallel from the source, strikes the beam splitter at 45". The beam splitter then transmits half of the light and reflects the other half. The transmitted and reflected beams strike the two mirrors oriented perpendicular to... 

The heart of the optical hardware in a FT spectrometer is the interferometer. Nowadays, the most common set-up used is the classic two-beam Michelson interferometer shown schematically in Fig. 5.1. It consists of two mutually perpendicular plane mirrors, a fixed mirror Ml and a movable one M2. A semi-reflecting mirror, the beam splitter, bisects the planes of these two mirrors. A beam emitted by a source S is split in two by the beam splitter. The reflected part of the beam travels to the fixed mirror Ml through the distance L, is reflected there and hits the beam splitter again after the total path length of 2L. The same happens to the transmitted radiation. However, as the mirror M2 is not fixed at the same position L but can be moved very precisely back and forth around L by a distance x, the total path length of the transmitted part is accord-... 

Figure2.1 shows the simplest form of a Michelson interferometer. It consists of two perpendicular plane mirrors, one fixed and one movable to introduce the required...

Fig. 2.1 The simplest Michelson interferometer, consisting of two mutually perpendicular plane mirrors, one of which can move along an axis that is perpendicular to its plane. A collimated light source red) reaches the beamsplitter, which splits the light in two paths reflected blue arrow) and transmitted green arrow). The fixed mirror reflects the light back to the beamsplitter, and the movable mirror reflects the transmitted light to the beamsplitter, where they interfere...

The principle of a Michelson interferometer which is used in a Fourier transform infrared (FT-IR) spectrometer is illustrated in Fig. 2.4. As seen in Fig. 2.4(a) the device consists of two plane mirrors, one fixed and one moveable, and a beam splitter. One type of beam splitter is a thin layer of germanium on an IR-transmitting support. The radiation from the source is made parallel and as seen in Fig. 2.4(b), strikes the beam splitter at 45. The beam splitter has the characteristic that it transmits half of the radiation and reflects the other half. The transmitted and reflected beams from the beam splitter strike two mirrors oriented perpendicular to each beam, and are reflected back to the beam splitter. 

Figure 6.5. Optics of a very simple FT-IR spectrometer Si, source, Li, HeNe laser Mi, plane mirror M2, M5, Me, and M7, off-axis paraboloids of varying focal lengths M3, moving interferometer mirror M4, fixed interferometer mirror BSIR, beamsplitter Di, detector. Note that mirrors M2 and M5 have a hole drilled through so that the laser beam can pass to the laser detector, LD.

Another solution is to use cube-corner mirrors, which consist of three mutually orthogonal plane mirrors. The mirror system reflects any incident ray back in the opposite direction. The first very high resolution cube-corner interferometer that really worked was the Oulu interferometer in Finland. The Oulu interferometer is basically a Michelson interferometer, where the moving and the fixed mirror are cube-corners. If the corners are perfect, the tilt problem completely disappears. The only disadvantage of this type of interferometer is a shearing problem, i.e. the lateral shift of the moving cube-corner. This is the... 

These include rotation axes of orders two, tliree, four and six and mirror planes. They also include screM/ axes, in which a rotation operation is combined witii a translation parallel to the rotation axis in such a way that repeated application becomes a translation of the lattice, and glide planes, where a mirror reflection is combined with a translation parallel to the plane of half of a lattice translation. Each space group has a general position in which the tln-ee position coordinates, x, y and z, are independent, and most also have special positions, in which one or more coordinates are either fixed or constrained to be linear fimctions of other coordinates. The properties of the space groups are tabulated in the International Tables for Crystallography vol A [21]. 

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