Infrared radiation wavelength regions

INFRARED RADIATION. The region of the electromagnetic spectrum hetween the wavelength limits 0,7 and 1.000 micrometers. The lower... 

Infrared laser lines involving. .. 2p 5s —. .. 2p 4p transitions in the 3.39 pm region are not particularly usefiil. However, they do cause some problems in a 632.8 nm laser because they deplete the populations of the. ., 2p 5s states and decrease the 632.8 nm intensity. The 3.39 pm transitions are suppressed by using multilayer cavity mirrors designed specifically for the 632.8 nm wavelength or by placing a prism in the cavity orientated so as to deflect the infrared radiation out of the cavity. 

Radiation with long wavelengths falls in the infrared, microwave, or radio frequency regions. Heat lamps make use of infrared radiation, microwave ovens cook with microwave radiation, and radio and television signals are transmitted by radio waves. 

For infrared measurements, cells are commonly constructed of NaCI or KBr. For the 400 to 50 cm 1 far-infrared region, polyethylene is a transparent window. Solid samples are commonly ground to a fine powder, which can be added to mineral oil (a viscous hydrocarbon also called Nujol) to give a dispersion that is called a mull and is pressed between two KBr plates. The analyte spectrum is obscured in a few regions in which the mineral oil absorbs infrared radiation. Alternatively, a 1 wt% mixture of solid sample with KBr can be ground to a fine powder and pressed into a translucent pellet at a pressure of —60 MPa (600 bar). Solids and powders can also be examined by diffuse reflectance, in which reflected infrared radiation, instead of transmitted infrared radiation, is observed. Wavelengths absorbed by the sample are not reflected as well as other wavelengths. This technique is sensitive only to the surface of the sample. 

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