Fig. 12.2 Block diagram of an absorption spectrometer

The modulator is a device that interrupts the radiation several times in a second and converts the signal to an alternating current which is then used for recording. This is useful for amplification of signals and also to reduce the noise levels in the spectrum.

Fig. 12.3 A typical absorption spectrum

Three absorption regions are shown. The one at high frequency is very sharp, while the other two are broad. The width of spectral lines is governed by the uncertainty principle.

∆E .   ∆t   ≥ ћ/2                                                          (12.8)