Michaelson interferometer

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.

What is the distance that a mirror in a Michaelson interferometer must move to have a resolution of 1.0 cm-1 in the infrared ... 

In 1986, a Raman instrument based on NIR excitation (1064 nm) and a Michaelson interferometer became available [16]. This development revolutionized Raman spectroscopy. In addition to the advantages of throughput and multiplex inherent to Fourier Transform (FT) techniques, this instrument overcame the obstacle of fluorescence. Fluorescence was eliminated by excitation at a NIR wavelength where electronic transitions in most samples are absent. Availability of such NIR FT-Raman instruments was particularly useful in the studies of lignin. 

The operation of FTIR spectrometers has been described in detail elsewhere, (see, for example. Refs. [4, 64]), as have the advantages of these over dispersive instruments [4, 5, 64]. Briefly, the heart of an FTIR spectrometer is the Michaelson interferometer (MI) (Fig. 6). The infrared beam leaves the source, S, and is incident on a beam-splitter, B. Fifty percent of the light is transmitted to a moving mirror, MM, and 50% to a fixed mirror, FM. On reflection, these rays recombine and interfere at the beam-splitter before reaching the detector, D, via the window, W, and reflective working electrode, WE, of the spectroelectrochemical cell. The system also includes a reference laser, RL, which follows the same path through the interferometer, after which it is intercepted and directed at the laser detector, LD. 

B, beam-splitter Di detector FM, fixed mirror IR, infrared beam L, laser beam LD, laser detector Ml, Michaelson interferometer MM, moving mirror ... 

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