2 - Why chose a fourier transform spectrometer?

Abstract

The magnitude of information flow through a spectrometer may be thought of as the product of two quantities, one determined by the spectrometer optics and the other by the detector. Because of its axis of symmetry, the Fourier transform spectrometer (FTS) interferometer has a large entrance aperture and, consequently, a large AΩ product. Another aspect of the quantity of data obtained is the fact that the FTS records data at all frequencies simultaneously, a process called multiplexing. There is a great saving in observation time when one wants to look at many frequencies. Many problems do not require the full resolution of instruments. For these problems, it is useful to have variable resolution, because excess resolution reduces the signal-to-noise ratio. The FTS is especially flexible in this regard and has no equal in the ease of setting the instrumental resolution to the required value. If 1% line shape distortion is necessary, then an FTS with an optimum aperture will require five resolution elements across a line width. In contrast, the grating with an optimum slit width will require 30 elements across a line width. The factor of 6 in required resolving power is a large part of the practical advantage of an FTS. The FTS is the system of choice in the infrared under almost any conditions (with or without a multiplex advantage), and in the visible and UV when high accuracy is required in intensity, line shape, or wave number.