Precise calibration of zero-crossing temperature and drift of an ultralow expansion cavity with a clock transition spectrum

We report a clock transition spectrum approach, which is used to calibrate the zero-crossing temperature and frequency drift of an ultralow expansion (ULE) cavity with a Hertz level resolution. With this approach, the linear and nonlinear drifts of the ULE cavity along a variety of controlled temperatures are clearly presented. When the controlled temperature of ULE cavity is tuned away from the zero-crossing temperature of the ULE cavity, the cavity shows larger and larger nonlinear drift. According to our theoretical analysis and experimental results, we investigate more details of the drift property of the ULE cavity around the zero-crossing temperature, which has seldom been explored before. We can definitely conclude that the zero-crossing temperature of our ULE cavity used in an ytterbium (Yb) lattice clock is around 31.7 degrees C.