Temperature analysis of low-expansion Fabry-Perot cavities

Temperature dependent structural distortion at the contacted mirrors of low-expansion glass cavities can introduce changes to the cavity length independent of the length of the spacer. There are resulting temperature sensitivities of the path (m/K) at each end of a cavity that are proportional to the difference of the coefficient of thermal expansion (alpha) at the contact. The temperature sensitivity of the resonant frequency can be a minimum at a temperature T(C) if the product of length times alpha(T(C)) of the spacer approximately offsets the combined sensitivities of the ends, even if alpha(T(C)) of the spacer is significantly nonzero.