Effects of a magnetic field on the optical properties of dielectric mirrors

We have measured the changes in the polarization state of a monochromatic (λ=514.5 nm) light beam on reflection at normal incidence by a multilayer dielectric mirror placed in a time-modulated magnetic field. The dominant effect is a Faraday rotationΦ?3.7×10^?10 rad/G. The sensitivity (around 40Hz) obtained is ( simeq 6 times 10^{ - 9} {text{ rad/}}sqrt {{text{Hz}}} ) which is dominated by the shot-noise limit (100 mW of light power).