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Evanescent W ave Imaging 121

deposited on a 1-mm-thick polycarbonate substrate. The spectra
illustrate that ATR Raman can be conducted on moderate scattering
materials with excellent axial and volumetric resolution.

4.8 Conclusions
Evanescent imaging using visible light was first demonstrated by
5
Harrick in 1963. Harrick’s justification for developing the method
cited several maladies (e.g., mongolism and Turner’s syndrome)
and viral infections that modify the nature of the human skin pat-
tern. He theorized that by studying the abnormal infant’s hand-
print, it may be possible to detect these maladies at an early stage.
Although this method was based on physical means, the extension
to vibrational (molecular) spectroscopy enables the detection of
chemical differences related to disease. In the short span of 15 years,
infrared evanescent imaging has gone from concept to routine
analysis in the analytical laboratory providing the researcher with a
powerful tool for the study of disease etiology and detection. The
major benefit of the method, relative to conventional TF infrared
microspectroscopy, is that it provides enhanced spatial and volu-
metric resolution. In addition, it overcomes many of the spectral
artifacts associated with a TF analysis. Due to these advantages, it is
anticipated that pathologists will come to accept the method more
readily than the current means. The next big step for ATR imaging
will be the application of the method for quantitative studies.
Finally, although ATR Raman imaging is by no means routine, tech-
nological innovations over the next few years and the fact that this
method provides even better spatial and volumetric resolution than
infrared methods, could make routine ATR Raman imaging a tech-
nology to pursue.

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