![]() Where \(\theta’\) equals the angle of refraction in the air gap. Here all constructively interfering radiation is focused onto a screen where it creates a dark or bright spot. This causes an absorption spectra, as shown below. The remaining radiation reflects back and forth between the plates and is eventually transmitted through the pair of plates towards a focusing lens. When photons of light pass through a gas, the photons with the same energy as the energy gaps in the atoms can be absorbed. Some of the radiation reflects out of the plates back towards the incident source. Diffuse, multi-beam incident radiation passes through a lens and is directed to the plates. An interferogram is a photographic record produced by an interferometer.Ī Fabry-Perot Interferometer allows the incident radiation to be reflected back and forth between a pair of reflective plates that are separated by an air gap (Ingle). All other radiation suffers destructive interference and is therefore removed from the spectrum. In the region, 711 microns (1430910 cm-1) there are many absorption bands and even pairs of almost identical organic molecules show up differences here. When the beams are recombined, only the radiation that is in phase when the beams recombine will be detected. No two organic compounds have the same infrared spectrum and so individual, pure compounds can be identified by examination of their spectra. Some systems also include a beam splitter that divides the incident beam and directs each portion along a different path before being recombined and directed to the detector. Interferometers are also non-dispersive systems that use reflectors (usually mirrors) to direct the incident radiation along a specified path before being recombined and/or focused. Note that when the incident radiation is normal (perpendicular) to the filter surface, then the transmittable wavelength is independent of the radiation angle: ![]() This shows that for a given material (constant d, \(\epsilon\), and m) changing \(\lambda\) results in a different \(\theta\). Where \(d\) is the thickness of the dialectic material (on the order of the wavelength of interest), ? is the refractive index of the material, \(m\) is the order of interference, and ? is the passable wavelength. ![]()
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