Volume relaxation of quenched silica at room temperature monitored by whispering gallery mode resonance wavelength

We used a resonance wavelength shift of a whispering gallery mode to monitor volume relaxation at room temperature in cylindrical and spherical resonators fabricated by quenching the molten tip of a pure silica optical fiber. The high sensitivity of the method allowed measurement of the linear dimension at sub-ppm resolution. All the resonators registered a volume increase in the first few hours, in agreement with the volume-temperature equilibrium curve of type IV silica below the glass transition temperature. When heating of the fiber was insufficient, the volume increase was greater, ascribed to a larger volume of strained silica. We also formulated thermodynamics to estimate the temperature coefficients of polarizability at constant pressure and at constant density from resonance shift data obtained in experiments performed on relaxed silica resonators.