What Determines Resolution in an FTIR Scan

Since interferogram data points are obtained at evenly spaced intervals, high-resolution scans require more data points and hence greater optical path differences than low-resolution scans. Thus there is a relationship between resolution and optical path difference as follows  

Equation 2.8 takes the form of a reciprocal because high resolution is denoted by small numbers and low resolution by large numbers. 

When one types the desired instrumental resolution into the FTIR software, the instrument determines the maximum optical path difference to use in the measurement by rearranging Equation 2.8 as follows  

The Relationship between Instrumental Resolution, Optical Path Difference, and Mirror Translation for a Michelson Interferometer 

According to Equation 2.9 a 4-cnr resolution spectrnm requires an optical path difference of 1/4 cm, an 8-cm resolution spectrum requires an optical path difference of 1/8 of a cm, and so on. Equation 2.3 shows that for a Michelson interferometer optical path difference is twice mirror translation. Eor example, if the maximum mirror translation during a scan is 1/8 cm the optical path difference is giving 1/4 cm and hence a 4-cm resolution spectrum. Table 2.2 shows the relationship between instrumental resolution, optical path difference, and mirror translation for a number of common resolution settings. 

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