Faraday Rotation in Air: Combining Brute Force and Finesse

Because of the weak circular birefringent response to axial magnetic fields, and hence low values of the Verdet constants, only a few research groups have successfully measured non-resonant Faraday Rotation in diamagnetic gases. In contrast to those complicated schemes, we utilized a straightforward technique resulting in accurate measurements of the Faraday rotation in air. Our method combines brute force (a magnetic field intensity of around 210 gauss over a 60 cm length), and finesse (differential phase sensitive detection), resulting in accurate values for the Verdet constant of air, $V_{air,}$ at a dozen wavelengths ranging from 405-800 nm, which can be modeled as a mixture as $V_{air} =$ (0.7809 $V_{N2} \quad +$ 0.2095 $V_{O2})$.