Determining absolute thermal expansion of titania-silica glasses: a refined ultrasonic method.

Specific test conditions for determining ultrasonic velocities in titania-silica glasses are shown to improve the experimentally established linear correlation between velocity and thermal expansion. Finer surface finish, normalized thermal history (annealing), and controlled temperature for the test specimen improve the relationship. A statistical analysis shows that 5-35 degrees C average expansion coefficients can be accurately predicted from ultrasonic velocities with a standard deviation of 1 ppb/ degrees C. Excellent agreement is established between the ultrasonic predicted expansion and test results supplied by the University of Arizona Optical Sciences Center.