Attenuated Total Infrared Internal Reflectance ATR Spectroscopy Spectra-Tech

6 Attenuated Total Infrared Internal Reflectance (ATR) Spectroscopy (Spectra-Tech) 

ATR spectroscopy is a versatile and powerful technique for IR sampling. Minimal or no sample preparation is usually required for rapid analysis. ATR is ideal for those materials that are strong absorbers. In addition, ATR is a useful technique for providing information about the surface properties or condition of a material. 

The condition that must exist for total internal reflectance is that the angle of the incident radiation, 0, must exceed the critical angle, 0. The critical angle is a function of the refractive indices of the sample and ATR crystal and is defined as  

A property of the evanescent wave that makes ATR a powerful technique is that the intensity of the wave decays exponentially with distance from the surface of the ATR crystal. The distance, which is of the order of micrometres, makes ATR generally insensitive to sample thickness, allowing for the analysis of thick or strongly absorbing samples. 

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