Patent ID: 6906327

Claim:
A non-destructive method of measuring a characteristic of a coating on a substrate, the method comprising: transmitting an infrared beam into a crystal in contact with a coating on a substrate; reflecting the infrared beam within the crystal; detecting the reflected infrared beam at a first wavelength and a second wavelength that is different from the first wavelength; comparing infrared energy I c1 of the reflected infrared beam at the first wavelength with a predetermined value of infrared energy I o1 of a reflected infrared beam at the first wavelength that is reflected within a reference crystal that is not in contact with the coating to determine an absorbance value A 1 for the coating at the first wavelength; comparing infrared energy I c2 of the reflected infrared beam at the second wavelength with a predetermined value of infrared energy I o2 of a reflected infrared bean at the second wavelength that is reflected within the reference crystal that is not in contact with the coating to determine an absorbance value A 2 for the coating at the second wavelength; and correlating a relationship between A 1 and A 2 to a measurement of a characteristic of the coating.