| coefficient established by determining the relationship between the absorption of two wavelengths, one with minimal absorption due to OH impurity, the other with high absorption due to presence of OH impurities in the crystal lattice |
α is the infrared absorption coefficient;
t is the thickness of the Y-cut sample, in centimetres;
T1 is the per cent transmission at a wave number of 3 800 cm–1 or 3 979 cm–1;
T2 is the per cent transmission at a wave number of 3 410 cm–1, 3 500 cm–1 or 3 585 cm–1
Note 1 to entry: The OH impurity creates mechanical loss in resonators and its presence is correlated to the presence of other loss-inducing impurities. The α-value is a measure of OH concentration and is correlated with expected mechanical losses due to material impurities.