Micro ATR imaging

Since ATR image involved the sample being measured in contact with an ATR crystal of high refractive index, n, the spatial resolution is unproved according to Eq. 1 and 2 [18], When germanium is used as the ATR crystal, which has a refractive index of 4, the spatial resolution achieved can be improved up to four times when compared to transmission using the same optical objective. The field of view in micro ATR imaging is ca. 50 x 50 pm2. 

Figure 1.28 Micro-ATR images of the PMMA film on a silicon wafer shown in Figure 1.24 obtained by integrating between (a) 1 753 and 1672cm- (X , = 5.8 am) and (b) 1179 and 1090cm- = 8.8 am). Reproduced with permission from...

Another field of application, especially for ATR imaging, is that of pharmaceutical formulations. Here, in 2003, Chan et al. reported the first results on macro and micro ATR imaging of pharmaceutical tablets by characterizing the spatial distribution of active ingredients and excipients [19]. Further examples in this field are described in Chapter 10 of this volume. 

The applicability of ATR-FT-IR imaging ranges from micro ATR imaging using a microscope objective to the use of ATR accessories with focused or expanded optics, without need to use the microscope. The ATR crystal in a prism shape... 

The applicability of ATR FT-IR imaging ranges from micro-ATR imaging using a Ge microscope objective to the use of ATR accessories with focused or expanded optics without recourse to the microscope [3]. Thus, the range of areas in the samples that could be measured simultaneously using FPA detectors and a prismshaped ATR crystal is from 500 pm X 700 pm to 1.6 cm X 2.1 cm (see Section 9.2.3 for further discussion). The measured area with macro-ATR imaging depends on the specific optics used in these ATR accessories and also on the size of the pixels in the array detector. Most of the currently used detectors have a pixel size of 40 pm X 40 pm or 60 pm x 60 pm. 

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