coefficient established by determining the relationship of the transmittance at two infrared wavenumbers
Note 1 to entry: The absorption measurement is carried out at the following two wavenumbers:
- at the reference wavenumber (3,800 × 105 m–1 or 3,979 × 105 m–1), where the infrared absorption is very small,
- at the absorption wavenumber (3,500 × 105 m–1 or 3,585 × 105 m–1), where the infrared absorption due to hydroxyl (OH) impurities in the crystal lattice becomes large.
Note 2 to entry: Hydroxyl (OH) impurities create mechanical loss in resonators and their presence is correlated with the presence of other loss-inducing impurities. The infrared absorption coefficient is a measure of hydroxyl (OH) concentration and is correlated with expected mechanical losses due to material impurities.
Note 3 to entry: The infrared absorption coefficient is expressed by the following equation using the logarithm base 10:
where α is the infrared absorption coefficient;
t is the thickness of the Y-cut sample, in centimetres;
T1 is the transmittance at a wavenumber of 3,800 × 105 m–1 or 3,979 × 105 m–1; T2 is the transmittance at a wavenumber of 3,500 × 105 m–1 or 3,585 × 105 m–1.
|