13.4 : 红外光谱仪

In a dispersive infrared spectrometer, the radiation produced by the hot wire is divided by mirrors into two parallel equal intensity beams that pass through the reference and sample cells.

Its monochromator consists of a beam chopper that passes the beams alternately towards a slowly rotating diffraction grating prism which varies the frequency or wavelength of the radiation.

A thermocouple detector senses the intensity ratio of both of the beams.

Finally, the signal from the detector is amplified, and the recorder draws the spectrum.

A Fourier transform infrared spectrometer involves an interferometer, wherein the radiation passes through a beam splitter, a fixed mirror, and a moving mirror, before it reaches the sample.

The beam splitter separates the beam into deflected and undeflected radiations, which are allowed to fall on fixed and moving mirrors, respectively.

The two beams recombine at the splitter to produce an interference pattern or an interferogram containing a wide range of wavelengths or frequencies.

The detector detects the interferogram modified by the sample, and the computer extracts the individual frequencies using the Fourier transform operation.