This very important instrument had its origins in the interferometer introduced by Michelson in 1891 for the examination of high-resolution spectra. It is more often used today in the form of a Twyman-Green interferometer, which is essentially a Michelson interferometer used with collimated light. The Twyman-Green was introduced to test the figure and quality of optical components; it has more recently become the basis of many Fourier transform spectrometers (FTSs). The use of interferometers as spectral analysis instruments was pioneered by Felgett, Jacquinot, and Strong. Other interferometers can be used for obtaining spectra, but only a few are appropriate for use as imaging spectrometers.
11.1 Two-Beam Interference
When two monochromatic beams of light are superimposed, an interference pattern is set up. If Î¨ 1 and Î¨ 2 represent the complex electric fields of the two beams that are combined, the expression for the interference pattern is E=1 2 Î⋅ 0 <â£Î¨ 2 â£<=1 2 Î⋅ 0 Î¨â
Î¨ ∗ =1 2 Î⋅ 0 [Î¨ 2 1 +Î¨ 2 2 +2Î¨ 1 Î¨ 2 cosÏ)], where E stands for the average flux density, the irradiance pattern, and Î¨ is the electric field; this is the time-averaged version of Eq. (2.3). The optical quantity that is sensed is the time average of the square of the electric field.
© 1997 Society of Photo-Optical Instrumentation Engineers
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