The birefringence of a low-loss, high-reflectance coating applied to an 8-cm-diameter sapphire crystal grown in the <i>m</i>-axis direction has been mapped. By monitoring the transmission of a high-finesse Fabry–Perot cavity as a function of the polarization of the input light, we find an upper limit for the magnitude of the birefringence of 2.5 × 10<sup>−4</sup> rad and an upper limit in the variation in direction of the birefringence of 10 deg. These values are sufficiently small to allow consideration of <i>m</i>-axis sapphire as a substrate material for the optics of the advanced detector at the Laser Interferometer Gravitational Wave Observatory.
© 2001 Optical Society of America
Jordan B. Camp, William Kells, Martin M. Fejer, and Eric Gustafson, "Measurement of Birefringence of Low-Loss, High-Reflectance Coating of M-Axis Sapphire," Appl. Opt. 40, 3753-3758 (2001)