Fixed mirror

In an FTIR spectrometer, a source (usually a resistively heated ceramic rod) emits infrared radiation that is focused onto an interferometer whose main components consist of a beamsplitter, fixed mirror, movable mirror, and detector. The beamsplitter divides the beam into two beams. One beam is reflected off the beamsplitter toward the fixed mirror and is then reflected back through the beamsplitter to the detector. The other beam is transmitted through the beamsplitter toward the movable mirror and is then reflected off of the beamsplitter and to the detector [1],... 

Fig. 6.15 Smallest possible fixed mirror, formed by a stable arrangement of four particles. BBMCA rule (e) (see figure 6.12) is successively applied to even (i.e. thicic-lined) and odd (i.e. thin-lined) partitions of the lattice.

To get over this difficulty, FTIR uses the basic principle of an interferogram. A source of IR light (containing a broad band of IR frequencies) is incident upon a fixed mirror, but passes through an optical device, the beam splitter at which about half the light is reflected and half allowed to pass through shown in Figure la ( ). 

There are two light sources involved, a white light and a laser source. The white light uses the same moving mirror and therefore makes up a second interferometric system within the spectrometer. When the moving mirror and the fixed mirror of this secondary interferometer are equidistant, a centerburst is produced which is... 

Fig. 5.20. (Top) Schematic diagram of a Michaelson interferometer. Retardation determines difference in optical path between fixed mirror and moving mirror. When retardation, S, is 1/2 light with a wavelength equal to A will be reinforced. (Bottom) Interference pattern from the Michaelson interferometer. Major peak where S = 0 is where all wavelengths are reinforced.

Figure 4.5 Schematic diagram of a Fourier transform infrared (FTIR) spectrometer. Infrared radiation enters from the left and strikes a beam-splitting mirror (BS) angled such that half of the beam is directed towards a fixed mirror (Mi) and half towards a moveable mirror (M2). On reflection the beam is recombined and directed through the sample towards the detector. M2 is moved in and out by fractions of a wavelength creating a phase difference between the two beam paths. This type of device is called a Michelson interferometer.

An interferometer is a device that utilizes a moveable and a fixed mirror to manipulate the wave patterns of a split light beam to create constructive and destructive interference in this beam. 

Fig. 7.—The Michelson Interferometer (BS = beam splitter, FM = fixed mirror, and MM = movable mirror).

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