Speaker
Description
Fluorides like MgF2 and AlF3 have the lowest refractive index among the known coating materials; using them in a high-reflection (HR) Bragg mirror instead of SiO2, one could reduce the total HR coating thickness and hence its coating thermal noise.
A succession of annealing treatments at different temperatures (but with the same duration) were performed on a silica disk coated with MgF2. The annealing was done in a controlled Argon atmosphere, in order to prevent the oxidation of the coating. After each annealing cycle, the Q-factor and the weight of the sample were measured, in order to extract the coating losses.
We noticed that after each annealing treatment, the Q-factor of the sample increased, but started to decrease above 500°C.
We repeated the succession of annealing treatments with different durations (but at the same temperature) on a different sample, identical to the previous one.
In this case we noticed that the Q-factor of the sample increased after each annealing, until the fourth treatment (that correspond to 124 hours of cumulative annealing times).
