Figure 7.8
Interferometer and associated electronics.movements of mirror B along the direction of the radiation beam incident upon it causes constructive or
destructive interference between the two halves of the recombined beam as the optical path difference
between them is altered. Continuous movement of B backwards and forwards over a short distance
generates a dynamic interference pattern or interferogram that can be monitored by the detector. The
interferogram is sampled several thousand times by the microcomputer during one cycle of the mirror
movement, which takes about 0.1 second, and a digitized representation of it stored in memory. The
digitized interferogram is mathematically related to the spectral output of the source, i.e. its spectrum,
which can be derived from it by performing a point-by-point fast Fourier transformation (FFT), a
process accomplished by the computer in less than 1 second. If the radiation is then