Question

Explain the principle of ATR. What are the two optical conditions for ATR?

Answer 1

IR beam is directed into a crystal of relatively higher refractive index. The IR beam reflects from the internal surface of the crystal and creates an evanescent wave, which projects orthogonally into the sample in intimate contact with the ATR crystal. Some of the energy of the evanescent wave is absorbed by the sample and the reflected radiation (some now absorbed by the sample) is returned to the detector.

Two optical conditios to be met are

ngle of incidence of the IR beam is should not be low and the refractive index of the crystal should be high.